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  • Question asked 2017-12-14 10:47:16 ... Most recent comment 2017-12-16 19:04:32
    Paint Mediums
    Question

    ​Has there been any modern improvement upon casein secco painting media after buon fresco (lime plaster) wall painting. Specifically, are there synthetic media (acrylics or alkyds etc.) that work well with lime? I was curious to know if anyone may have tried Zecchis "secco" paint that indeed contains an acrylic binder, however I am not sure what else may be in it. and i am not sure that it was intended for lime plaster buon fresco.

  • Question asked 2017-12-15 23:09:45 ... Most recent comment 2017-12-16 18:51:56
    Oil Paint Grounds / Priming
    Question

    ​Hello,

    I've been working on a soapstone carving and have produced a ton of dust in the process. I was wondering if I can use it in place of marble dust to make gesso? Would it be a stable ground for oil painting?

  • Question asked 2017-12-16 03:20:42 ... Most recent comment 2017-12-16 18:47:09
    Gilding
    Question

    ​Three questions:

    1. I would like to add portions of burnished gold leaf to my oil paintings. I have oil gilded on canvas before and though the results were fine I much prefer the look of burnished gold. Which support would be best suited for this? Gessoed ACM? Gessoed Panel?  

    2. I have read you cannot burnish oil gilding but have never seen the reason why. Why can't you burnish oil gilding?

    3. I would also like to gild a ram skull. Archivailibity is less inmportant in this case but I would still be pleased to do it in an archival manner. Which mordant should I use and should I prepare the bone in any particular way?

  • Question asked 2017-12-13 11:04:29 ... Most recent comment 2017-12-16 18:32:52
    Flexible Supports
    Question

    ​I have been researching commercial, cotton, oil painting papers by D'Arches, Canson, etc, for detailed, preparatory studies that I may or may not mount and sell.  

    Do you forsee any problems with 100% cotton papers by these or other companies?

    The paper fibers are protected, according to their literature, but the OMS and oil can be drawn down below that surface somewhat, unlke the pH neutral PVA size layer tha I put on my papers before use.   Perhaps this affords more tooth for the paint layer to attach to.

    Any thoughts?

    Thank you.

    PS   I avoid priming papers as I will thereby lose the very texture that I like in the paper, and have been sizing only.   Also, the investment in time and material makes them so "precious" that I may not be as likely to experiment with them.   I have followed the directions sent by Robert Gamblin some 15 years ago.

  • Question asked 2017-12-14 21:23:38 ... Most recent comment 2017-12-16 18:26:31
    Gouache Matting, Framing, and Glazing Oil Paint Watercolor
    Question

    ​Hello MITRA folks ~ From a conservator's standpoint, can you tell me if there is justification for the wide-spread perception that watercolors are "fragile" and a "poor long-term investment" relative to an oil painting? I've always reasoned that an oil painting is *far* more prone to damage and degradation in both the short and the long term compared to a well-framed watercolor (modern lightfast paints, acid-free materials and UV glazing), since there is, at best, only a thin varnish to protect the oil's surface. Thanks for your thoughts.

  • Question asked 2017-12-15 19:44:40 ... Most recent comment 2017-12-16 09:42:16
    Acrylic Grounds / Priming Other Paint Mediums
    Question

    ​I am making some “ Calder like” Mobiles but instead of just spray painting them I’m interested in painting them using Acrylic paint.  Has anyone had experience with this and if so what is your experience/ pitfalls etc.? As well, I would like to know what kind of Primer or Ground that I would have to apply as a first protective coat ...I.e. once the metal is cleaned can I just spray on an off the shelf rust free Primer paint  or is there a material that I could use that would work better...e.g. gesso, medium etc?

    Thx. Hy

  • Question asked 2017-07-09 17:43:58 ... Most recent comment 2017-12-15 20:04:20
    Acrylic Rigid Supports Sizes and Adhesives
    Question

    ​I want to try using thick, solid cardboard as a surface for acrylic painting, but I can't get any information about its archival properties (lignin, acidity) from the manufacturer. I found a recipe on an acrylic paint manufacturer's website that calls for coating the entire sheet with a couple of layers of gloss acrylic medium-varnish so as to make a layer onto which one can paint. Supposedly, if any problems arise in the future (from what I know, it's inevitable with cellulose), a conservator will simply be able to dissolve the cardboard and reline the acrylic painting.

    I would like to ask how viable this idea is.

    Also, I thought about whether it would be more likely to work if I:

    1. saturated the cardboard with something (gelatin/methylcellulose/PVA/wall paint primer?), then
    2. gave it three layers of gloss medium (first diluted 1:1), then
    3. put on two layers of acrylic ground

    and then painted on it? I'm not sure if three layers of medium plus two layers of ground wouldn't be too excessive.

  • Question asked 2017-11-30 13:09:30 ... Most recent comment 2017-12-10 10:30:58
    Oil Paint Pencil Drawing Materials
    Question

    ​From a durable standpoint, can you tell me if drawing lines into wet oil paint with a graphite pencil is a sound practice? (On both stretched canvas and on panel.) Ultimately, the finished paintings would be varnished. I've Googled this question and come up with nothing...thank you!

  • Question asked 2017-06-15 16:48:30 ... Most recent comment 2017-12-09 22:02:38
    Oil Paint Paint Additives Paint Making
    Question

    ​GReetings, 

    When making oil paint or modifiying oil paint with additives, how do you determine the ratio of pigment to oil, say titanium white with marble powder to linseed oil? 

    There is a point when the paint becomes very thick and will even roll off of the mixing plate glass, and this is obviously too much pigment to oil. Are oil absorbtion rates needed, if so are these online?


    Thank You

  • Question asked 2017-12-08 17:31:10 ... Most recent comment 2017-12-09 19:18:03
    Technical Art History Oil Paint Paint Mediums
    Question

    Hi-

     

    I'm rather old school and I can't afford to switch to walnut oil and lavender I have to keep it simple.  I paint a lot and on a large scale. I would say my application of paint is on the wet loose side and most likely too much vehicle and medium is slapped around by your standards

    As I get older I am concerned with my health, if it is not too late, so I  have begun to rethink my formula of 40 years:

     1:1:1

    Turp- Dammar -Linseed oil

    I begin with gum turp and progress to a fatter medium.

    Occasionally I add stand oil to the brew.

    I have experimented with adding egg yolk, using liquin and alkyd mediums. I'm happy with my old "go to" but for the fumes. I occasional remove dammar from the mix. Any ideas of a formula or medium that would suit me. Any big issues with the 1/3, 1/3, 1/3 mixture I use?

    Thanks

  • Question asked 2017-12-08 18:53:25 ... Most recent comment 2017-12-08 22:05:00
    Flexible Supports Studio Tools and Tips
    Question

    ​I recently had occassion to remove several less-than-satisfactory paintings from their stretcher bars (in preparation for attaching new canvas) and discovered that these brand-name, pre-stretched canvases had been stapled on the corners of the bars on the front side. Am I understanding that this practice of stapling the corners of stretcher bars totally defeats the function of "wedges" for adjusting loose canvases? Thanks for your thoughts.

  • Question asked 2017-12-08 05:34:33 ... Most recent comment 2017-12-08 16:32:06
    Oil Paint
    Question

    ​Can anyone please point me towards a scanning electron microscope image of the surface of a sunken in oil paint swatch, and preferably an image of a glossy swatch for comparison, that I could use for a teaching slide? Thank you.

  • Question asked 2017-12-05 22:08:25 ... Most recent comment 2017-12-06 12:45:58
    Sizes and Adhesives
    Question

    In 2015 I contacted Gamblin asking for directions on a substitute product to RSG for sizing canvas.  The recommendation I received were instructions, developed by Robert Gamblin and Ross Merrill, former head of Conservation at the National Gallery, in point form.  After a few steps on how to glue canvas to a wood panel, Step 6:  Apply Gamblin PVA size to protect the surface of the canvas with one penetrating coat.

    I decided to purchase the PVA Size and after a few tests, and problems with the ground being too absorbent, I decided to apply 3 coats instead of 1, sanding and scraping before applying the last coat.

    On a Facebook forum I was informed that Gamblin PVA size had been tested by Sarah Sands (article dated 2013, Preparing a Canvas for Oil Painting | Just Paint,)  She tested the PVA size along with other products, and her findings showed that Gamblin PVA Size performed poorly, both in terms of flexibility and strikethrough.

    I am a bit puzzled by this:  Gamblin is providing me with instructions with big names undersigning them, plus "National Gallery" and the "Canadian Conservation Institute" are mentioned on the labels and online.   But then you have Sarah Sands, doing an honest test, showing that the Gamblin PVA size should not even have the name 'size' on it.  I am no expert, but I can read a chart.

    My question is, what is going on here? 

  • Question asked 2017-12-05 14:05:54 ... Most recent comment 2017-12-05 23:03:50
    Pigments Oil Paint
    Question

    ​Hello all,

    I have long wondered about certain pigments still used in quality artist paints that are rated as less than excellent in terms of lightfastness: in what situations will they tend to fail, and how might we best use them to achieve lasting results? Some of the pigments I have in mind are PR112 (Napthol red), PY3 (Arylide Yellow),   or even  NR9 (Madder Lake). It's my understanding that pigments such as these are much more prone to fade in tints, but I'm wondering if there are any applications that are considered truly lightfast, such as in glazed top coats etc..

    This question is primarily about these pigments in oil paints but i'd welcome any insights regardless of medium.

    Thank you very much in advance for any advice you can offer, and thank you all for the work that you do!

    Bob

  • Question asked 2017-11-19 11:56:20 ... Most recent comment 2017-12-02 17:17:43
    Acrylic Grounds / Priming Oil Paint Rigid Supports Flexible Supports
    Question

    ​In the Resource section (Grounds & Primers) MITRA states that, "Even though acrylic grounds/paints appear to dry within 24 hours, moisture continues to evaporate from these materials over an approximate 30-day period." Does this mean that supports (both canvas and panel) primed with Acrylic "Gesso" should not actually be painted on (this would be for oils) until *after* this 30-day period has passed...?

  • Question asked 2017-01-03 15:41:54 ... Most recent comment 2017-11-30 09:04:46
    Paint Additives Paint Mediums
    Question
    I don't know what to make of the claims of a medium made of copal resin that is modified with heat  and mimics the charactoristics of the older fossil forms of copal or so says its makers. It is relatively new and is a gel. Is this possible? I have read about the more desired effects of the older (fossill ) forms of this resin and would like to know about the virtues and shortcomings of copal in general.
  • Question asked 2017-11-28 01:27:08 ... Most recent comment 2017-11-28 20:50:49
    Oil Paint Drying Oils Paint Mediums
    Question

    ​Someone just stated in the "Painting Best Practices" facebook group that coldpressed linseed oil is mechanically superior to alkali refined linseed.
    Is there any truth to this?

    I'm not taking about yellowing, but film strength, flexibility and adhesiveness. (Maybe longevity too.)
    Have there been any studies about this?

  • Question asked 2017-11-23 19:22:07 ... Most recent comment 2017-11-26 21:00:27
    Oil Paint Rigid Supports Grounds / Priming Acrylic
    Question

    ​Greetings MITRA folks. Can you tell me if oil painting directly on a shellaced panel is an accepted and durable practice? I know of at least one company which sell panels that have been "sanded and shellaced on both both sides and edges with a wax-free shellac," and they are advertised as a "ready-to-use painting support." I know of both acrylic and oil painters who use these particular panels, but I do not know if they are adding an oil or acrylic ground over the shellaced surface before proceeding with oils. Knowing only of shellac from a furniture sort of standpoint, I would have thought that shellac as a surface for oil paints *directly* would be too slippery and would have poor long-term adhesion. Would you kindly set me straight on this subject? Thank you! 

  • Question asked 2017-11-22 14:19:04 ... Most recent comment 2017-11-26 19:14:00
    Chalk Paint Mediums
    Question

    ​Hello Mitra,

    I wish to mix calcium carbonate to my paints to give them more body and also to maintain them a bit more transparent. Is their a specific calcium carbonate that I should purchase for what i want to do? Or is it all the same?  Chalk? Marble dust? etc?

    Can I mix it directly to paint from tubes ,or should I start from scratch with powder pigment?  

    Thank you ,

    Hector



  • Question asked 2017-03-13 10:36:30 ... Most recent comment 2017-11-26 13:20:53
    Alkyd
    Question

    I looked at previous posts but still find the advice I've seen on using alkyd mediums a bit confusing and contradictory. On one hand I've read that it is best to use alkyd mediums only in lower layers because you want faster drying layers under slower drying layers. This makes sense to me. However, I've also seen recommendations from manufacturers to increase the amounts of alkyd medium in subsequent layers to maintain fat over lean (more flexible over less flexible?) but that seems to contradict the slow over fast drying concept. Ultimately, I would like to use M. Graham solvent free  walnut akyd medium in the underpainting/blocking in and then straight oils in subsequent layers. Would I need to worry about a) adhesion between the first and second layers or b) violating fat over lean/ more flexible over less flexible? 

  • Question asked 2017-11-25 11:39:09 ... Most recent comment 2017-11-26 11:31:44
    Sizes and Adhesives
    Question

    ​Hi! Im an art student at the National academy of fine art Oslo, Norway.   

    I'm interested in using raw linen canvas in my painting, I've previously bought white  grounded linen and stretchid it the unprimed back as the front. Recently, I received unprimed linen from artist store.

    I have experience with rabbit skin glue but since i want to use oilpaint directly on the "size" this is not on option?. I started using artist grade PVA, and a professor tought me how to dilute it with water, ca 1/5 pva to water. it worked well with two coats on cotton but when i started priming the linen the result was really horrible.

    i stretched the raw canvas nicely and tight on a stretcherframe and started brushing on pva/water.  while wet the linen got really firm and tight but after drying overnight the canvas was completely slacking.  after yet another coat the canvas was tight (wet) and later turned slacking but hard as the pva dried.  i made tests where i put on the pva undiluted and the result was good but the pva layer dried almost instant, it was uneven and slighly milky plastic looking.  

    I also started pva priming the canvas unstretched and later had to really struggle to force the canvas to get tight on the frame with canvas pliers, as it did not get really stretched i made the huge mistake to brush some water on the canvas, it get really bad after drying, untight and full of ripples. i have made alot of searching for answers, my proffessors just told me that the key is to dilute with water, and restretch the canvas and give it more glue coats. wich i did, and every time the same thing, tight when wet and loose dry.     

    after i while i found this article,  its the same problem i encountered with pictures 

    http://dianamosesbotkin.blogspot.no/2013/10/pva-horror-tale.html?m=1  


    i read that professional canvas maker like cleassens of belgium use acrylic glue to their canvases and coating both sides, is this a better option?   can you dilute pva with something other than water?

    I know about the Golden products but now i ended up with having alot of PVA and trying to make it work.     




     

        

  • Question asked 2017-11-08 11:25:44 ... Most recent comment 2017-11-25 09:49:45
    Oil Paint Rigid Supports Grounds / Priming
    Question

    ​I've searched here on the topic, and also read the "rigid supports" document in Resources (which is a wonderful reference), but I have a few additional questions about working on copper. 

    1. I'm using relatively thick copper (14-gauge etching plates) and working fairly small (maybe 11x14" or so, down to 5x7"). Is it necessary to brace supports of this size, or would it be sufficient to put a lightweight (floating) backing board behind the plate in the frame--perhaps Gatorfoam, or a layer or two of museum board? 

    2. My process to prepare the surface of the plate: degrease with denatured alcohol, thoroughly abrade the surface with sandpaper or steel wool (with the aim of completely stripping the surface to expose fresh metal), vacuum off any copper dust, then degrease again, making sure that all dust and residue gets removed. Then allow to dry, and prime. Does that sound about right?

    3. How about where the copper is not covered by primer/paint? Like the back and sides? Can I just let that oxidize, or should I seal it with something? Renaissance Wax, maybe? 

    4. I assume any oil-based primer will work? How about an alkyd primer, like Winsor & Newton's Oil Primer? I have a few small test sheets on which I tested some straight lead carbonate in linseed oil (RGH), a lead painting primer that contains some titanium white and driers (Rublev), and the Winsor & Newton primer. All three dried very quickly (the W&N primer was touch dry in a matter of hours). I'm guessing that the copper is a drying catalyst? The Rublev primer turned very green upon drying; I don't think that it was a matter of surface prep, because the RGH lead primer is right next to it on the same sheet of copper, and it didn't change color at all. The Winsor & Newton primer took on a slight green tint, but it's barely noticeable. Is this sort of thing common? Something to worry about? I don't think I'd use the Rublev primer, since the color change in that case was considerable. 

    5. I skipped the oft-recommended garlic step, just on the basis that I have been able to find a consistent or empirically supported reason for its use. Some sources say that it helps to "etch" the metal (though it is unclear how, since garlic is not acidic). Some sources say that it might serve as a wetting agent (which makes more sense, except for the fact that copper doesn't seem to need a wetting agent--it takes oil paint really well, with no beading). Some sources say that it helps the paint bind to the surface chemically, rather than just mechanically, but I don't think that's correct. Don't oil films exchange ions with copper? In any event, the idea of putting an aqueous paste between the metal and primer seems like a bad one to me, but perhaps there is a purpose for this step that I haven't considered?

    Thanks!


    -Ben



  • Question asked 2017-11-18 16:16:32 ... Most recent comment 2017-11-25 08:49:15
    Paint Additives Paint Mediums
    Question

    ​I usse oil glazes over a monochromatic egg tempera underpainting.tand Oil (1part Sstand Oil and 6 parts english turpentine) is not satisfactory. Normally my woerk requires 3- to 40 very, very thin oil glazes. Can you recommend a workable reciepe? Alklyd and other such "synthetic materials" are not satisfactory for me.

  • Question asked 2017-11-11 11:19:05 ... Most recent comment 2017-11-20 22:07:03
    Oil Paint Varnishes
    Question

    What did the old masters use to paint whisker thin long lines with oils? I have seen work by several Dutch masters but also the French Academics like Jerome and company who were able to manipulate paint and produce incredible details in a miniature scale, as if they were using a micron pen loaded with paint. I am trying to keep it simple, and I don't want to get into resins or magic media. I have found so far the best combo is to paint over a couch of linseed oil with paint + stand oil. The best brush so far is the size 0 spectre by W&N, but I am sure that are better brushes out there that work best for this purpose.  I know from trying that a lot of the success is in the manipulation of the paint and having a steady hand.  Correcting the shape of the paint with another paint, working in layers. Smaller brushes may produce better results + practice.  I am able and have produced similar details in my still lifes but the scale is not the same. It gets to a point where the detail is so small that I am not able to do in oils.  But if it is a resin, which one would you use.  My friend uses Amber from Donald Fels and Venice turps by Kremer pigments. Thank you.

  • Question asked 2017-11-19 11:16:06 ... Most recent comment 2017-11-20 13:57:41
    Paint Mediums
    Question

    ​ I was trained in a 15th century glazing technique that tries to mimick the process of the Van Eyck brothers. Sir Charles Eastlake alongside with the technical bulletins from the National Gallery mentíon the usage of resins in their mediums. The National Gallery bulletin particularly mentions pine resin, not just for the Van Eyck brothers but also for later flemish painters like Rubens and Van Dyck. Do you happen to know specifically what pine resin is? I currently use dammar but i'm not sure what pine resin actually is.

  • Question asked 2017-10-25 10:54:17 ... Most recent comment 2017-11-18 12:35:57
    Flexible Supports Oil Paint
    Question

    ​I've read that cotton canvas shouldn't be stretched at larger sizes for oil because it's too flexible, but that a heavier cotton can make up for what it lacks in strength. How does 15oz cotton compare to linen at sizes 8ft and above?

    Thanks!

  • Question asked 2017-04-25 14:20:23 ... Most recent comment 2017-11-18 12:30:08
    Paint Additives Oil Paint Paint Mediums Scientific Analysis Art Conservation Topics
    Question

    I have a query regarding the section in the MITRA documentation on Solvents about Clove Oil for Oil painting:

    "Essential Oil of Cloves or Clove Oil has been used as a preservative in emulsions and as an additive to mediums to substantially slow down their drying rate. There are far better preservatives available today. The use of clove oil as a drying retarder is greatly discouraged as its addition tends to substantially weaken the dried paint film.

    Other Essential Oils and Extracts are also periodically used in art making. Oil of rosemary sometimes served as a substitute for clove oil and as a component in the creation of complex oil-hard resin mediums. Like clove oil, artists should forgo the use of these materials as their dangers far outweigh and perceived benefits."

    I and many other painters I know use Clove Oil to extend the drying time and I have never read anything negative about using it before.

    Please can you tell me what evidence led to the conclusion that clove oil weakened dried paint film.

    What were the numbers for the control, clove and rosemary in the studies that were done?

  • Question asked 2017-11-16 13:20:58 ... Most recent comment 2017-11-16 15:45:16
    Rigid Supports
    Question

    Is it true that the hardboard used for the museum grade clayboard used for scratchboard is acid-free? Do I need to worry about outgassing? When I painted an "X" across the back to help prevent warpage, the Golden Titanium White acrylic paint immediately turned yellowish in hue. Why? As a precaution, should I coat the sides and back with GAC 100+500 (since it's chily in the house)?​

  • Question asked 2017-11-15 19:19:37 ... Most recent comment 2017-11-16 12:26:50
    Acrylic Rigid Supports Oil Paint
    Question

    ​This question is directed mainly at Sarah Sands (though anyone can feel free to weigh in): 

    Are there any particular concerns with using GAC 200 to seal the back and sides of unbraced Hardbord panels? I've tested a lot of different finishes for this purpose, and consistently find that GAC 200 performs better than just about anything else in this role. My criteria are two-fold: I'm looking for a coating that will provide some moisture resistance, and also one that will act as a sort of consolidant to strengthen the Hardbord (particularly the edges, which when damaged are prone to fraying). 

    Strengthening the Hardbord is probably the most important concern for me; in general, I don't find Hardbord to be all that reactive to humidity changes, but it can be vulnerable to physical damage, especially when dropped. With a couple of coats of GAC 200 on the back and sides, it seems much more durable. The cured GAC makes the edges very hard and, well, solid. I can drop a panel from eye level onto a hard floor--on a corner!--and it suffers no visible damage. An unsealed panel dropped in the same manner invariably ends up with a dented corner that imediately starts to fray. 

    The fact that the GAC dries relatively quickly is also a plus. I've gotten similar results with oil-based polyurethanes, but they require at least four coats to build to a film on Hardbord (which is very absorbent), and so drying time becomes an issue. Being able to seal the back of a panel in a day (rather than several) is helpful. I've also tried GAC 100, but it dries to a somewhat tacky surface, and does not harden the edges of the panel to the same degree that GAC 200 does. I know that GAC 200 is supposed to be more brittle, but it held up well to my impact tests. 

    So I guess the question is whether or not this is an acceptable use for GAC 200. Also, will it remain stable as a surface coating on the back and sides of a Hardbord panel, or should I top-coat it with something else?

  • Question asked 2017-11-06 14:54:53 ... Most recent comment 2017-11-07 20:05:12
    Drying Oils Varnishes Oil Paint
    Question

    ​Could you please talk a little about the practice of using isolating varnishes between layers of paint?
    Personally I don't do it, but some advocate it so it would be good to have some authoritive documentation to refer to.

  • Question asked 2017-11-02 15:35:27 ... Most recent comment 2017-11-03 18:10:01
    Art Conservation Topics Gouache Matting, Framing, and Glazing Studio Tools and Tips Varnishes Watercolor
    Question

    ​Hello MITRA folks...Would you speak to the issues from a conservator's point of view (especially concerning long-term cleaning, repair and UV protection) for the growing trend to varnish, wax and resin-coat finished watercolors as ways to avoid the cost and biases against "works under glass?" Your perspectives are much appreciated.

  • Question asked 2017-10-28 15:55:13 ... Most recent comment 2017-10-30 10:11:35
    Art Conservation Topics Other Scientific Analysis
    Question

    Hello, im a MA student currently working on some research projects. I would like to ask you for some advice (if this is not the place just tell me).

    One of the research im beggining with is about 'new digital technology uses in conservation of art' (3D scanning, ink-jet transfer reintegration, 3D reproductions, etc) . I was looking in to related bibliography or other information but there is not much of it, so I would be gradefull if you suggest some information or examples of new digital technology used in conservation, or if you know any book or institution (i.e. factum-arte) regarding this topic.

    Thank you.

  • Question asked 2017-09-27 15:45:45 ... Most recent comment 2017-10-28 16:40:30
    Photo-Documentation / Digital Printing Pigments Technical Art History
    Question

    An interesting question for you!

    ​I would like to do a reproduction of one of my favourite paintings, Vermeer's 'Girl with a Pearl Earring'.

    I have found the excellent close up scanned image that the Mauritshuis have in their collection:
    https://www.mauritshuis.nl/en/discover/mauritshuis/masterpieces-from-the-mauritshuis/girl-with-a-pearl-earring-670/

    I can see that there is a lot more detail in the darks than I've seen in other images. However I understood that the blue of the turban was made with natural Ultramarine and Lead White, yet the blue in the turban looks a little blue green to me, rather than blue red.

    Other images I've seen have the painting with more of a blue-red cast on the turban and on other parts of the painting: 
    https://upload.wikimedia.org/wikipedia/commons/6/66/Johannes_Vermeer_%281632-1675%29_-_The_Girl_With_The_Pearl_Earring_%281665%29.jpg

    I was wondering if any of you knew if the colours in the real painting are more accurately shown in the mauritshuis scan, or in the second link from wikimedia.

    Thank you!
    Richard

  • Question asked 2017-10-24 16:52:44 ... Most recent comment 2017-10-25 15:51:53
    Drying Oils
    Question

    ​I have always worked under the stricture that linseed oil based paints and mediums, with at least some lead white in the paint layer, produced the the toughest, most flexible paint layer possible.

    However, considering that I work on rigid panel, not on stretched linen when this advice was likely first made... 

    Q #1  Would it be adviseable to switch to safflower or walnut based oils and mediums instead, considering that they yellow less, or at least more slowly?

    Q #2  How important is a flexible paint layer on a rigid support?


    For people who are concerned with the slower drying rate of safflower and walnut, I have found that the slower drying rate can be mitigated by placing the painting into an enclosure with incandescent bulbs, which will bring the temperature up to F 90-100.

    Q #3   Do you see any problems with placing the wet paintings in a warmer environment for more rapid drying?   


    No added driers are needed. 


    Thanks for your thoughts.  

  • Question asked 2017-10-24 17:05:07 ... Most recent comment 2017-10-25 14:46:59
    Grounds / Priming Rigid Supports
    Question

    ​Q #1   Are there any advantages to oil primers over acrylic dispersion ones for creating the best adhesion to the paint layer on a rigid support?

    The oil primer, I suspect, would create both a mechanical  and chemical adhesion to the paint layer, whereas the acrylic dispersion primer would create only a mechanical one...or is the mechanical adhesion great enough that it would easily suffice on a rigid panel?


    Q #2  If using oil primers on rigid panels, would the primer need to cure for several months to a year before using?

    Information in your "Resource" section suggested that the dried primer merely needed to resist the fingernail before using.


    Thanks for your thoughts.

  • Question asked 2017-10-14 15:13:18 ... Most recent comment 2017-10-25 13:33:58
    Oil Paint
    Question

    ​Is Arches Oil Paper an acceptable support for an oil painting with a long life? Alternatively, do we know what makes this oil ready, in a way that is different enough from what you usually call paper, which is not oil ready due to the rot attack of oil to the paper fiber? (Perhaps this paper is a synthetic polymer?) I am aware of some other common problems associated with painting on non rigid supports, but am interested in using marouflage techniques to adhere to panels for greater stability. Is adhesion of paint on paper-in general- for impasto technique problematic?

    If oil was the medium usually used for hand touching photos, do these have acidic oil rotting issues?


    Sorry for the host of inquiry, I am a curious person:) Thanks for any ingith into the oil paper etc.

  • Question asked 2017-10-23 13:29:21 ... Most recent comment 2017-10-24 00:17:23
    Technical Art History
    Question

    ​I have studied art materials off and on since 1990 and own copies of several of A. P. Laurie's books and those of D.V. Thompson, Ralph Mayer, Cennino Cennini, etc.   I am still interested in the historical development of art materials and practices over the centuries but do not take them seriously as sound, modern studio art practices.   No search for the elusive "secret mediums" of the old master here.

    Q #1   Except as a study of the history of art conservation/art materials, how useful are these books to the art student wishing to use the most permanent materials and practices?  


    So many of the materials discussed are either discontinued, replaced with more permanent ones, changed in chemical composition but with the same name, etc,  or altogether unavailable, that it seems as if it would only serve to confuse the new artist.   I know that it did years ago when I first started studying them and my mind often swam with conflicting advice.  


    Q #2   With more recent research and knowledge of art conservation and materials, how far back can we depend on books on art materials and practices?   20 years, 40 years, more?


    Q #3   Ralph Mayer died ca 1980, so how reliable are updates to his books?


    Its a shame that we do not have more authors who are well versed in chemistry to help with the technical aspects like A.P.Laurie but The Artist's Assistant , by Leslie Carlyle, Archetype Publications, 2001, while not a painting methods book, has a lot of useful, modern  information on many older practices and art materials.


    Thanks for your thoughts.



  • Question asked 2017-10-05 20:11:57 ... Most recent comment 2017-10-19 11:47:31
    Oil Paint Other Paint Additives Paint Making Scientific Analysis Studio Tools and Tips Technical Art History
    Question

    I am in the copyist program at The Met, copying The Flight into Egypt by Tanner, link below:

    https://www.metmuseum.org/art/collection/search/16947 

    In searching for more information about Tanner's techniques, I came across this 2011 presentation:

    https://www.youtube.com/watch?v=hWxErF_nzd4

    My questions are specifically about the content from 33:20-34:46. 

    I'm trying to figure out two key techniques. First- the dragged paint technique. Brian Baade mentioned this briefly in the presentation for the Near East Scene-Mosque in Tangier painting. In trying to achieve the same effect, I can't seem to get my paint to break. I buy my pigments, not make my own. Do commercial pigments come with too much oil? Is there some way of getting a dryer paint? Second- the impasto texture of the paint in The Good Shepherd. Brian Baade mentions that he doesn't know what method was used to apply paint, but I thought I'd ask about what tools/techniques were found to produce the most similar result.

    Thanks,

    Karri

  • Question asked 2017-10-16 16:16:57 ... Most recent comment 2017-10-17 13:11:47
    Varnishes Oil Paint
    Question

    ​I want to do a painting (on canvas or on acrylic-gessoed paper) in charcoal and oil but I'm unsure how to "fix" it or varnish it.  I love charcoal and usually just use it for the sketch underneath the oil and then paint over it but what happens if I do a painting that has a combination of areas with only charcoal on it, some areas that are paint only, some areas that are paint and charcoal together, and some areas with charcoal over the paint? The oil would be very thinly applied. Would I use a spray varnish at the end to "fix" it because a brushed-on varnish would lift the charcoal? If on paper, should I frame it with a good space between the glass and artwork? If y'all think that charcoal and acrylic paint would be better for this type of art, what would I use in that case to seal it? Thank you for this helpful site. 

  • Question asked 2017-10-13 10:35:14 ... Most recent comment 2017-10-13 12:06:29
    Pigments
    Question

    Do you have an exact recipe for extracting Fra Angelico blue from lapis lazuli? A student of mine needs the recipe for his conservation degree, but his professor also wants more scientific quantities. Cennino cennini's recipe for natural ultramarine is too vague for their MA classroom. Ex: how strong should the lye solution be and it's ideal ph? How much ashes to water? How much lazuli to resin, wax and oil? Etc. Thanks

  • Question asked 2017-10-11 21:18:05 ... Most recent comment 2017-10-12 21:52:33
    Grounds / Priming Oil Paint Studio Tools and Tips
    Question

    ​🍁 Fall Greetings, MITRA folks ~ Can you tell me if there is any technical reason to NOT paint light-to-dark in thin layers of oil with an alkyd walnut medium over a thin Titanium White (no Zinc) first layer on the acrylic gessoed surface? 'Durable' is my concern. Any thoughts would be much appreciated. 🍂

  • Question asked 2017-10-12 15:58:50 ... Most recent comment 2017-10-12 20:22:58
    Flexible Supports
    Question

    Is it safe to wash unused canvas in the washing machine? If not, can it be washed by hand? I came across a lot of 15 oz. cotton but it has some dirt in spots and deep creases that can't be ironed out.


  • Question asked 2017-10-10 15:33:41 ... Most recent comment 2017-10-12 11:55:38
    Egg Tempera
    Question

    ​My understanding was that Andrew Wyeth used a traditional chalk and glue gesso, learned from his brother-in-law Peter Hurd, under his egg temperas paintings.  I presumed this from various articles I've read; also from a Mr. McNeil (I think his name was), an older gent (he was in his 90s when I met him 20 years ago) who used to run a company called Permacolors and told me he made traditional chalk and glue gesso panels for "Andy".   However someone else recently told that Wyeth worked on caesin gesso. Can Dr. Joyce Stoner (or anyone who knows) corroborate what ground Wyeth worked on?  

    Thanks,  Koo Schadler

  • Question asked 2017-10-10 12:35:23 ... Most recent comment 2017-10-11 17:51:41
    Egg Tempera
    Question

    ​​Many years ago I bought a product called Disponil from, I think, Kremer Pigment in NYC - it worked great at combining hard to wet pigments with water.  I haven't been able to find Disponil again.  I now use Golden Paint's Universal Dispersant.  Am I safe in presuming that the Golden's product is compatible with egg tempera (for pigments that resist wetting)?  Any other comments on dispersants and egg tempera?  

  • Question asked 2017-10-10 11:04:40 ... Most recent comment 2017-10-10 18:26:00
    Acrylic
    Question

    ​I've heard that  a little 4F pumice, added to  acrylic primer, creates a smooth oil painting surface on rigid panels but with a little more tooth to grab onto the paint.   Acrylic primer alone seems a little slick for me, but I do not necessarily need great absorbancy.  

    Any problems?

    Would this surface be too abrasive for bristle or sable brushes?

    Would the pumice increase absobancy? 

    Thanks for your thoughts.

  • Question asked 2017-10-10 11:46:05 ... Most recent comment 2017-10-10 16:39:02
    Flexible Supports
    Question

    ​Do you see any delamination or other problems with oil paintings made  directly on PVA sized, 140 lb, cotton wc paper, rather than on an acrylic primed paper?


    I've been using sized, 140 lb,  cotton wc paper for oil studies and small paintings for for 18 years without problem.   The paper has a texture that I enjoy and I size them on one side with 2 coats pH neutral PVA size, (75% water-25% PVA glue), as suggested by Robert Gamblin.   The size is allowed to dry in between coats. 

    I do not apply an oil or acrylic primer as it tends to smooth the very texture that I like and I can collect hundreds of small plein air studies and sketches on paper, for reference, without the massive weight and volume that mounting on hardboard or dibond would entail.   The paper is stiffer than the same on unstretched linen so that studies can be more easily be handled.

    On occaision, I mount them on panel for sale.   Again, no problem in the years that I have had paintings on paper mounted on panel, but I thought that I would check with you anyway.    

    I realize that the primer would likely be more absorbent and may create a better mechanical bond with the paint layer, but I've seen so many plein air studies of 18th - 19th C masters painted and/or mounted on a lot worse supports and often without sizing.

  • Question asked 2017-10-08 04:40:02 ... Most recent comment 2017-10-10 15:50:19
    Grounds / Priming
    Question

    ​Dear Moderator

    I am trying to find a way of working that produces the best possible combination of characteristics for my way of working I currently have a thin linen which I want to adhere to panel once I do a decent painting on it Because it's fairly thin it's not taking the acrylic size well despite using a good acrylic matte medium in two coats which I've previously tested and used without problems With this linen however I'm getting strikethrough of oil paint on tests I've made Consequently I thought I'd try sizing it with the same medium then applying a couple of layers of good quality acrylic primer to prevent this strikethrough and then a final coat or two of my preferred lead oil primer Does this seem a reasonably sound given that ultimately it will be adhered to a panel? PS sorry most of my punctuation keys are refusing to work! 



  • Question asked 2017-10-06 19:28:03 ... Most recent comment 2017-10-06 22:12:49
    Sizes and Adhesives
    Question

    Dear Moderator. I am trying to find a way to get a smoother surface for portrait painting in oils as I'm regularly encountering lumps and bumps in my lead oil primed linen. I've tried gently abrading the raw linen, pre sizing,  with a pumice stone, which did help, but now find the acrylic size I've applied is quite rough to the touch. I'm using Liquitex matte medium diluted 1:1 with water and plan to apply 2 coats. I know about the need for a size to penetrate the fabric rather than act as a distinct layer. I'm not trying to achaieve a glassy surface just a smooth one. By the way, I intend to glue the painting to a panel once it's finished. I'm concerned that using sandpaper or pumice stone on the size will actually remove the size to the point hat it no longer performs its function of sealing the canvas. Is this a legitimate concern and if so what can I do about it?  

  • Question asked 2017-10-06 11:18:16 ... Most recent comment 2017-10-06 13:00:52
    Rigid Supports
    Question

    ​Hello, 

    I found a great source for copper supports and am familiar with how to prepare them.  I was curious though, as metal supports become a bit more pliable at larger sizes, what sort of glue would be recommended for mounting them?  I wouldnt want one to get accidentally dented from the front or back once framed and finished

    If mounting to wood, should I glue 100% of the surface to take into account the woods hygroscopy?  Or would it be better to 'hang' the mounting from the top, as one would when framing a drawing? I imagine it would be an easier process to mount to ACM panel.

  • Question asked 2017-10-06 11:37:19 ... Most recent comment 2017-10-06 12:17:19
    Varnishes Ink Oil Paint
    Question

    I have an oil painting that was signed in ink.  the written text was done with a micron colorfast brush pen/marker (recommended by one of the conservators here).  

    It is now time to varnish that painting, just got it back, though completed in 2014.  I usually use regalrez (gamvar) to varnish these days- though I am slightly concerned that brushing over the ink portion will cause it to run/bleed?  I would like to make sure to varnish over the signature to protect it as well.

    My current plan is to put a light aerosol spray varnish over the part in ink, perhaps two lightly sprayed coats, and let it cure for a couple of days before brushing varnish over the entire picture.  How does that sound to the mods here?  

  • Question asked 2017-10-01 21:45:08 ... Most recent comment 2017-10-05 19:49:39
    Flexible Supports
    Question
    My paintings tend to be larger (7',8',9') and can be quite fragile. To help protect them, I have typically stretched the unprimed canvas over a cradled wood panel. My first question is whether or not this is actually beneficial, or whether the panel is unnecessary? The canvas rests over the wooden panel but is not glued down.

    Recently I've been considering going back to stretcher bars (probably aluminum) and inserting a lightweight foam into the stretchers attached only to the cross bars, so the perimeter could still be stretched if necessary. My second question is whether or not this is a more permanent solution?

    I do not have access to gator board, because I can't  find single sheets and the shipping is outrageously pricey. I do have access to foam core and 1/2" and 1" sturdy construction insulation foam (which seems more rigid and doesn't have a paper veneer).  My third question is whether foam core or the construction foam is worth using/and or dangerous in terms of off gassing etc. to the back of the canvas? 

    My fourth question would be if you all have any better solution/suggestions I hadn't considered.

    Thanks!
  • Question asked 2017-09-27 14:12:45 ... Most recent comment 2017-09-28 16:50:52
    Rigid Supports
    Question

    I would like to mount some 10" x 20", oil studies on pH neutral PVA sized, 140 lb wc paper, onto 4 mm dibond using acrylic dispersion medium.   I suspect that this is not optimal, but wish to frame the studies.

    Will a water based "adhesive", such as acrylic dipersion medium, take hold of a roughened, non absorbent, dibond surface?

    Am I headed for trouble?

    Have done the same on gatorfoam, in  smaller sizes, without problem in the past.   The wc paper is stiffer than linen and doesn't seem to buckle or bubble in these small sizes, unlike linen.

    Read the pertinent posts and information in the resources section, but it did not specifically address finished oil studies, on paper, being mounted onto dibond, hence the above question.   

    As dibond is not absorbant, coating both sides of the panel should not be necessary, correct?

    Thanks for your help.

  • Question asked 2017-09-13 05:33:23 ... Most recent comment 2017-09-26 23:14:56
    Alkyd Drying Oils Grounds / Priming Industrial and Non-Traditional Products Paint Mediums Oil Paint Solvents and Thinners Rigid Supports Scientific Analysis Varnishes
    Question

    Hello MITRA,

    I might win the prize for bringing the most problematic query to the forum. The reason being that my methods of using oil paint are unorthodox, and I don't have the most scientific of minds. But please don't be too hasty to judge my methods. I have spent years of time and money getting to the point I have, and I am approaching you now seeking a little reassurance/guidance, but also knowing that you may not be able to give it.

    Where to begin. Essentially, I dilute oil paint to the extent of being able to pour apply it (alarm bells ringing already, I know). I mix oil paint in different concentrations, with a combination of solvent and medium, that when poured onto a flat laid rigid support (these days a primed Aluminium Composite board), they interact and react against each other in desirable and unpredictable ways as they meet and combine- natural forms, even fractal patterns, appear within the very dilute paint. detail.jpg Once this layer is dry, after a few weeks, I paint glazes on top in a more controlled manner. 

    What I seek in pouring oils, is a contradiction really: Stable instability.

    I know the basics...that if you just dilute oil paint with solvent it can't bind properly and will chalk off.. so I've alwyas been careful to add oil/alkyd medium of some kind. I also know the fat over lean rule. But when I am throwing it all on together in one liquid layer- I can't really apply it that rule in the same way... 

    The first year I was making paintings like this I used just solutions made of Turpentine and Linseed Oil, but I encountered drying and yellowing problems which I since have understood… I then adapted my method and started using drying mediums instead of linseed oil.

    The main successful recipe I have used is:

    - Liquin mixed with Zest it solvent, and Oil paint.

    I think and hope I am using enough of each, for the paint to be just strong enough to cure and not peel off. It has has made many successful dry and even paintings over the last 3 years. It gives a very thin, flat surface, almost like watercolour, once dry. It has had and almost enamel surface which succesffully took glaze on top. But I do find that it has sunk in significantly since I changed primer to Thixtropic alkyd primer (which i thought would be better on Aluminium panels) but I have read that some primers make sinking in worse.  I used to use an oil primer, which I think I will return to. 

    Q: Does it matter if a painting surface is sunk in... if I don't mind the look of it being uneven? Is the worry that any varnish will bond with the paint and not be able to be removed? – does this even matter? Can I use a few thin coats of spray retouching varnish to seal it and then later a proper varnish on top? Would that top layer of varnish be able to be removed if I did that? Is there a big danger of the painting yellowing /darkening a lot like this, even if I use thin layers of spray varnish? (winsor and newton).

    The only problem with the Liquin is that it darkens over time, and actually has over quite a short period of time in recent paintings: compare detail (liquin) early 2017.jpg with detail (liquin) late 2017.jpg . I don't mind how it has changed and darkened.. but I would like to know if you think it will continue to darken more and more..

     Because of this darkening issue, but still wanting to avoid yellowing oil.. The second and most recent recipe I am trying is :

    -'Drying Poppy Oil' with Zest it solvent and the oil paint. 

    I have started experimenting with this because poppy oil is supposed to be good for pale colours… and I use a lot of white, very pale and muted colour fields. (which is another issue.. finding the best white for using large amounts..currently using Permalba Original. But thinking of trying lead white?! As if I hadn't already made like hard enough for myself!). drying poppy oil detail.jpg  I knew poppy oil itself would be far too slow drying for what I do, but thought the one with driers added to it might work? The early stages of the experiment and I have managed to achieve a dry and even surface.. glossier than the liquin ones. But I have yet to try painting glazes on top of this layer. Q: I have heard that poppy oil is more likely to crack, is this true also of drying poppy oil? In which case, would you say the surface I have now that seems smooth and slippery, will eventually crack over time?

    So there you have it.

    I don't know of any oil painters historically to employ methods like these, I do know artists that have done this kind of thing using Acrylic or resins. I can only find one other artist online that claims to be using a similar technique in oil: 

    https://mauricesapiro.com/viscosity-series-poured-paintings/

    But other than his comparative technique, I have not found any other information to help me navigate this process. I suspect that would be because it is unadvised to be diluting and pouring oil paint in such a way for all the potential instabilities it causes..  But it is partly the instability that makes me want to paint in this way in the first place! You see the dilemma!

    I am happy with the paintings currently as they are.. in the short term, they seem stable. But I am concerned with the long term. I would obviously like to avoid Extreme yellowing and and peeling off of any paintings in the future! It is not the end of the world if they change and crack a little bit. But if it is going to be a lot, then I would feel unethical in selling the works. OR I do you think I should include a clause when selling that says I can not vouch for the archival quality of the work?

    I am aware that what I am trying to achieve would be probably be far easier and perhaps more straightforward if I used acrylics instead- (it would sure be a lot cheaper!)… but I am not quite ready to give up on the beautiful effects I can achieve using oil paint, everything I have invested in experimenting. 

    Any tips, or even educated guesses, on ways I could be doing this better - mediums that are good for making a strong but pourable paint film?! Ratios I should keep to? or other ways to keep the work stable for as long as possible... would be greatly appreciated. Thank you! sorry this has been such a long and confused essay...

     

  • Question asked 2017-09-26 13:51:45 ... Most recent comment 2017-09-26 17:59:21
    Rigid Supports Paint Mediums
    Question

    ​I have been warned about the dangers of using Resins in mediums.  My understanding is that the issue is twofold:  on is in cracking of the paint layer itself ( possibly yellowing as well) and then also in conservation as the removal of the resinous varnish layer would also affect/remove a portion of the paint layer.  
     I want to be very specific to the Resin and meidum that I use becuase  the answer may not apply to all resins and mediums equally.   I use 2 parts sun-thickened linseed oil, 1 part turpentine and 1 part Canada Balsam.
     I have a number of questions. 1. With respect to yellowing, would that not be mitigated by the varnish layer which would protect the paint. If the varnish yellows, it can be removed and a fresh varnish put on, so that yellowing is not an issue for the paint layers themselves?
    2.  To what degree is the cracking attributed to the rigidity of the painting surface and to what degree the resin in the medium?  Are the caveats for using Canada Balsam in the medium significantly reduced is the painting surface is a stable one?  Many thanks.



  • Question asked 2017-04-30 18:12:23 ... Most recent comment 2017-09-25 21:21:15
    Acrylic Health and Safety Paint Additives
    Question

    I am exploring the technique of acrylic pouring / flow acrylic / liquid acrylic art, and am looking for suggestions on cell creation. Many of the artists I have found online share assorted techniques such as using a silicone additive or floetrol, often in addition to using a heat torch of some kind. (A good reference would be the YouTuber Annemarie Ridderhof.)

    My question is this: is there an additive or process that I can use in place of some of the above additives, that are odorless (I have medical complications that make me very sensitive to smells) and are safe to be used? I fear that applying direct heat to acrylic and whatever additives being used, can potentially cause fumes with dangerous effects.

    For context, I generally use basic liquitex student grade acrylic paint with water on assorted sizes of stretched canvas.

    Many thanks in advanced for any tips or suggestions!


  • Question asked 2017-09-19 19:10:46 ... Most recent comment 2017-09-20 16:11:02
    Egg Tempera
    Question

    I'm planning some paintings in tempera grassa.  I've worked before in the medium, using an emulsion of egg yolk and sun-thickened linseed, almost equal parts each but a bit more yolk so it's water-soluble. The paint had good working properties, but I'd like a bit more hardness and shine, as one would get by adding dammar (which many tempera grassa recipes call for) but which I don't want to add (because of the negative attributes of dammar).  Is there another resin I could incorporate for a similar affect?  Would any of the modern synthetic resins be a possibility?

    Thanks,

    Koo Schadler

  • Question asked 2017-09-19 15:24:31 ... Most recent comment 2017-09-19 21:34:59
    Oil Paint Sizes and Adhesives Rigid Supports
    Question

    ​I've mentioned this in another thread, but haven't actually phrased it as a question, and I am curious what the MITRA folks think about using a thin sizing of Paraloid B-72 to reduce the absorbency of either Claybord or traditional gesso, prior to painting with oils. I mean, I know that it works, from a process standpoint, but is it a sound practice? 

    My own research on Paraloid B-72 suggests that it is one of the more stable synthetic resins and is not prone to yellowing, but like all acrylics, it is somewhat sensitive to solvents. Then again, it's incorporated into the ground (which in the case of Claybord, already contains acrylic resin), so is it really any worse than painting on an acrylic primer? 

  • Question asked 2017-08-30 05:17:59 ... Most recent comment 2017-09-18 15:37:19
    Pigments
    Question

    ​As some of you work for (or have close links with artist paint companies), I wonder if you were aware of any new paint pigments that are being tested by paint manufacturers at the moment? :)

  • Question asked 2017-09-16 10:41:07 ... Most recent comment 2017-09-18 11:34:42
    Acrylic
    Question

    ​Hello,

    I like using copper panels with oil paint. Do you know if copper panels and acrylic paint are compatible as well?

    Thank you

  • Question asked 2017-09-09 22:42:34 ... Most recent comment 2017-09-18 09:57:01
    Flexible Supports Grounds / Priming Oil Paint Sizes and Adhesives
    Question

    ​The store-bought stretched heavyweight canvases that I've used before have, it turns out, no sizing underneath their three factory-applied acrylic gesso layers. I am concerned about oil paint strike-through, and wonder if two (or more) additional layers of high-quality acrylic gesso would insure the canvas durability? I've read somewhere that acrylic gesso, being formulated for absorbancy, will always remain susceptible to oil strike-through. I'd love to hear your professional thoughts on the subject. Also, would you explain materials and technique for attaching a rigid covering to protect the back of a stretched canvas? Thank you so much.

  • Question asked 2017-09-14 09:41:01 ... Most recent comment 2017-09-14 19:35:53
    Art Conservation Topics Flexible Supports Grounds / Priming Oil Paint Pigments
    Question

    I've read all of the references here regarding Zinc White (PW4), and it seems that the current opinion is that it is best to avoid all applications of Zinc White (PW4) for oil painting due to durability issues, at least until further clarification from new research studies is available. Am I understanding correctly? Thank you for the clarification. Susan

  • Question asked 2017-09-05 18:12:26 ... Most recent comment 2017-09-11 15:15:23
    Acrylic Oil Paint Rigid Supports Industrial and Non-Traditional Products
    Question

    I have read that Polyethylene terephthalate is a good support for painting with acrylics, and decided to try painting on the sheet version of it. However, there are different variants of plastic sold under the general name "PET". I can buy:

    • APET (amorphous PET)
    • PETG (Polyethylene terephthalate glycol-modified)​
    • other variants with additions that claim to enhance UV-resistance, etc.

    My question is: are all of these equally fine as painting substrates? From what I've read, the glycol-modified version doesn't become hazy or brittle when heat-treated, but I don't know what type of heat would be required to be relevant for painting. Also, I'm not sure whether any of them would be more likely to leach anything (glycol?), or be more susceptible to propylene glycol present in paints.

    As a side question: is sheet PET compatible with oil paints?

  • Question asked 2017-09-06 18:35:00 ... Most recent comment 2017-09-06 19:12:08
    Oil Paint Paint Making Pigments
    Question

    ​Hi, I recently purchased some azurite pigment and I want to mull it into paint, I have never done this, It is my first time and I am wondering what is the right way to do it? should I wet the pigment first in water, or should I just add oil to the dry pigment. Also what oil is recomended with azurite

  • Question asked 2017-09-05 11:13:55 ... Most recent comment 2017-09-06 13:28:23
    Varnishes
    Question

    ​Daer MITRA 

    I have a painting that I finished recently which I wish to photograph for online entry to a competition. I had a fair bit of sinking in which I've tried to correct with oiling out, with reasonable results but there is still a certain dullness I would like to correct. I am planning to apply a good quality retouch varnish as a temporary varnish to my touch-dry painting as I feel it will bring out the colours etc. I couldn't find much information about using retouch varnish in this way (i.e. as a temporary varnish) in the resources section of MITRA. Apart from careful application technique etc, which I can read about here or in my Gottsegan book, is there anything I need to know or any reason to avoid retouch varnish? 

  • Question asked 2017-08-21 04:03:00 ... Most recent comment 2017-09-05 10:16:48
    Oil Paint
    Question

    ​Dear MiTRA person

    I recently purchased some oil paints by a reputable German manufacturer who sadly is not explicit about the oils used as binder. They admit to using a combination of oils but the feeling on online forums is that there is probably a preponderance of safflower or perhaps even sunflower oil. I have some concerns about using them because inevitably they must have added some driers and I am given to understand that some metallic driers like manganese can cause darkening in the paint film over time.  As is noted here in the resources articles, most paint manufacturers do add driers to one degree or another but the devil is of course in the detail ie how much? I've emailed them to enquire as to whether they have done any testing or have any reassuring information on this front but the response was a bit confusing as they kept directing me to information regarding the lightfastness of these paints. (And by the way they use the Blue Wool scale to assess lightfastness which as far as I know is very outdated!). Do I need to be concerned regarding darkening when using paints of this type? 

  • Question asked 2017-08-03 15:19:27 ... Most recent comment 2017-09-04 17:19:32
    Oil Paint Drying Oils Paint Mediums
    Question

    Dear MITRA,

    I encounter a lot of sinking-in due to the large fields of dark colors I use. I’ve been oiling out with straight walnut oil as a final layer in some cases despite the warnings for several reasons: 1) The brushwork is sucessful and seems a shame to repaint. 2) I don't have six months to wait for varnishing. 3) Even when I do oil out, then reapint, I often get more sinking it. 4) It solves the problem in the short term.

    I have read all of the posts relating to this topic (which have given me some good advise about other ways to mitigate the probelm) but still have several quesitons–

    If oil is rubbed into an acrylic ground to deter sinking-in, how does this affect the “fat over lean rule”? If a canvas is prepared this way, can one still paint with a medium that has solvent in it?

    If a layer of paint is oiled out with straight oil, does this mean one shouldn’t use any solvent in their next painted layer?

    I prefer to use straight walnut oil for oiling-out because it is thin and adding solvent can lift the paint, but I have read on this forum that more bodied oils thinned with solvent are better for oiling out. Why is a bodied oil thinned with solvent superior to a thinner straight oil?

    Can a black area of a painting be oiled out as a final layer? Is the inability for a conservator to remove this layer later on the only issue, since I assume true black won’t develop a yellow cast?

    How long does the yellowing process take to appear if a painting has been oiled out as a final layer?

    If cold wax is used in a medium to create a more even color field (i.e. less variation in shine), can the painting still be oiled out?

    Thank you so much.

  • Question asked 2017-08-31 01:46:50 ... Most recent comment 2017-09-01 17:51:00
    Oil Paint
    Question

    ​Hello,

    I am in the process of gluing earth magnets (and /or metal strips) to the backside (at the top) of both paper and canvas based paintings as a way to hang the works from metal screws. Is there an adhesive that you can recommend that could be both secure, and removable without damaging the support? 

    In the future I'd like the option to remove the magnets/ metal strips for more traditional framing options, and am looking for an adhesive that has these properties.

    (The paintings are oil on canvas, and oil on arches oil ready paper.)

    Thanks!

  • Question asked 2017-08-29 16:07:20 ... Most recent comment 2017-08-30 16:44:26
    Egg Tempera Oil Paint
    Question

    ​Have a great question that came in response to an article on Dark Yellowing we put out:

    "I realize that this is outside the scope of your study, but I am curious to know if the egg tempera medium undergoes yellowing when it is placed in a dark invironment."

    Any knowledge of dark yellowing being an issue in egg tempera? Curious minds want to know.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

  • Question asked 2017-08-25 23:45:53 ... Most recent comment 2017-08-26 16:03:34
    Art Conservation Topics Oil Paint
    Question

    ​I am wondering if there is a way to protect copper resinate from changing colors and turning brown, would an UV varnish help?

  • Question asked 2017-08-15 16:50:47 ... Most recent comment 2017-08-25 14:34:21
    Egg Tempera
    Question

    ​Hello MITRA,

    This question is a bit complicated, so please bear with me.  I have a fellow tempera painter who's experiencing cracking in the uppermost layers of her paintings. It starts out as very faint, fine lines that gradually increase with successive paint layers; the lines grow and evolve into fine "craquelure", and eventually tiny bits of paint flake off (within a few weeks of application).  

    Over the years I've heard from a handful of other tempera painters who've seen similar cracking, often (tho' not always) reported in areas of tianium white.  In general cracking (or craquelure) in tempera is rare, but with this most recent instance I'm recogninzing it as a problem for some painters and trying to understand it better.  I've come up with 5 reasons why cracking may appear in tempera paint:

     1. Excess binder. Too much yolk can create stresses as the protein molecules shrink with water evaporation.  

    2. Too thick a layer of paint. Tempera initially dries through relatively rapid evaporation of its water content, so if too dense a layer is applied it can crack as it shrinks (akin to a dried-out lake bed). 

    3. Adding too much water to tempered paint.  Once the paint is properly "tempered" it's possible to thin it significantly with water. However with TOO much water at some point the various components of the paint become so attenuated that it can create a weak paint film.   

    4. Over saturating underlying paint layers with water.  Research I've read on the effects of various solvents (both spirit and water) on egg tempera indicates that they can induce swelling in the paint films. If a curing paint film is compelled to repeatedly expand and shrink, this stress can weaken the bonds being formed in the polymerization process and create cracks (at least this is how I understand it; I'm not sure about this one...  By the way, none of the other reasons I suggest for cracking apply to the painter with the current craquelure problem; however she really saturates her surface with watery tempera paint, so much that the ground stays cool when her paint layeras are dry to the touch, suggesting there is residual mositure within - this is why I suspect this reason for her cracking problem, but I'm not sure). 

    5. Stresses in the ground and/or support. Cracks in the gesso and/or movement in the panel can telegraph up through paint layers.  

    My questions to the forum are:

    1. Has anyone else seen cracking in egg tempera paint layers? 

    2. What do you think of the above reasons?  Do they make sense?  

    3. Are their other potential causes of cracking?

    Thanks, Koo Schadler

  • Question asked 2017-08-19 11:48:53 ... Most recent comment 2017-08-22 21:59:14
    Ink Oil Paint
    Question

    ​I've read somewhere that shellac-based India Ink can be used for underdrawing before proceeding with an oil painting. Is that durable? Would the ink have to be full-strength, not diluted? I'm looking for an alternative to a solvent-thinned underdrawing that would still show through an Imprimatura. Would an ink underdrawing have to be completely covered by oil paint to be durable? I've seen Golden's article (Just Paint, Oct. 1, 2015) on underpainting alternatives (acrylics, watercolors, safflower oil-thinned paint and egg-oil-water thinned paint) and always wondered if those solvent-free alternatives needed to be completely covered with oil paint in order to be durable? For example, would a perimeter line in a solvent-free underdrawing need to be restated with full-bodied oil paint in order to be durable? Thank you for any thoughts.

  • Question asked 2017-08-19 16:30:15 ... Most recent comment 2017-08-20 01:54:54
    Oil Paint Art Conservation Topics
    Question

    ​Greetings,

    Perhaps this is out of the scope of the conservator, but I was looking at some very high res scans of a Caravaggio and looking for some professional insight into his working methods. Here is the scan: http://www.haltadefinizione.com/en/gallery/caravaggio-bacchus

    I know that reverse engineering a painting is difficult, but perhaps you have come across some convincing interpretations of how caaravaggio built his paintings- questions of source and optical devices aside, and I've read about the ambiguity of the incised lines- but can we speculate or measure his choice of grounds, layering process, glazing, mediums, working dark to light, etc? And this is obviously subject to change across works, but in this Bacchus, can you tell how he laid down paint to get to this end?

    His modelling of flesh tone seems 'ponced' or stippled on with a glaze, it is so delicate and doesn't seem to have any of the brush marks the lights have. 

    I've been reading V. Elliot´s Traditional Oil Painting, and he does some scholarly recreations of paintings, such as Bouguereau. Is there anyone that has does a similar analysis and receation of Caravaggio, that is accepted (I've seen some bad ones, and the work doesn't seem based on a grisaille to me)?


    Thank YOU!

  • Question asked 2017-08-17 22:02:15 ... Most recent comment 2017-08-18 23:23:30
    Grounds / Priming Other
    Question

    ​This may win the prize for the weirdest question... I have five maple panels that I sized and then later gessoed and left out on my porch to air dry. It's possible that a cat (or squirrel?) may have sprinkled them with their "marking fluid" while they were drying. (I've heard that cats are attracted to the smell of amonia.) There are a dozen or more shiny specs on each of the boards, which were laid end-to-end. And the peculiar and unpleasant odor is only slightly diminishing after a week and a half. I had thought maybe there was a reaction between the sizing and the gesso, but I think that would have resolved by now. So...if the panels have been sprayed, do you think it's a reasonable approach to clean them with vinegar and water 1:2? That's one of the home remedies that is suggested for spray on interior walls. I can wipe the specs off with straight water, but the odor seems to remain. I'm concerned about adhesion problems when I proceed with oil paint, or de-laminating further down the line. Alternatively, I could put another coat of gesso (water-based) on the boards, or an imprimatura of oil paint...? Any suggestions would be greatly appreciated!  :-(

  • Question asked 2017-07-13 10:14:14 ... Most recent comment 2017-08-18 12:41:36
    Watercolor
    Question

    A student recently showed me some watercolors of his that have a problem, hoping I could decipher it, but I don't know what's going on. Throughout several paintings there are areas where the paint is  (in his words) "disappearing" - initially the paint went on fine, but over time there are patches of paint loss that look a bit like a bug has been nibbling; or, another way to describe it, looks like someone pressed a paper towel with a squirrely pattern to areas of the paint while it was wet, lifting the paint (although, as mentioned, this problem didn't occur until after the paint had dried). Neither of these are the best description of the problem…I have photos, if there is a way to share images.  The paint loss is not limited to a single color and has occurred on several paintings with different types of supports.  All I could think of was minerals or salts in the water, precipitating out?  Any other ideas?

     

    Thanks,

     

    Koo Schadler

  • Question asked 2017-08-16 23:05:01 ... Most recent comment 2017-08-17 17:46:37
    Sizes and Adhesives Grounds / Priming Oil Paint
    Question

    ​Wondering about a couple different sizing options
    1. Gac 400 then two coats of Gac 100 then Rublev lead oil ground
    2. 2 layers of Gac 100 then Rublev oil ground

    How much of a difference will there be? Will the only difference really be in the canvas stiffness (with 1. being a stiffer canvas and 2. being more flexible)?

    Will there be any difference in how the oil paint sits on the surface?
    (For example) I do not like slick surfaces to paint on. I would like a semi absorbant surface. If I go with option 1, will the surface be too slick? Or will the overall surface be pretty much the same between the two?

    Thank you so much for any help!!



  • Question asked 2017-08-11 18:33:34 ... Most recent comment 2017-08-13 14:09:17
    Grounds / Priming Health and Safety
    Question

    Hello MITRA folks,

    Do you know if there are any alternatives to rabbit skin-based, solvent-based and acrylic-based grounds for both canvas and panels? I have read that methylcellulose can be subsituted, and a reference to shellac, but have read nothing definitive and scientific. This would be for oil painting, and I am looking for a low VOC, solvent-free, easy-to-use solution that would also be archival (or a support for oil painting that needs no ground (and no solvents to clean it) at all. 

    Thanks so much for any thoughts!

    Susan

  • Question asked 2017-08-09 14:26:38 ... Most recent comment 2017-08-11 19:14:16
    Oil Paint
    Question

    I was wondering if you have any advice/ways of testing adhesion between oil painting layers?  I have done a diy cross cut test with a razor blade and masking tape, but if I go by that thicker passages and impasto pretty much always fail, so it seems like overkill. On the other hand, a fingernail seems kind of weak, because I've not been able to scratch layers that I otherwise can peel or sand off relatively easily. 

    Thanks

  • Question asked 2017-08-08 17:06:40 ... Most recent comment 2017-08-09 15:19:08
    Health and Safety
    Question

    I will be mulling pigment and making paint for the first time and I want to be safe, what mask do you recommend me to buy (pigments might include vermilion, lead tin yellow, and azurite)

  • Question asked 2017-08-06 08:08:18 ... Most recent comment 2017-08-06 12:04:35
    Paint Additives Oil Paint Paint Mediums
    Question

    ​I have over some years been able to extend the life of oil paint on the palette and in small storage containers by the use of (Mark Carder's) Slow Dry Medium, in combination with the exclusion of air (oxygen). Mixed stock color is useable for two years and premixed values for two months in airtight glass jars.

    If I were to place a wet oil painting in an oxygen rich tent (storage bag) would I be able to accelerate drying to the point I could varnish earlier than the recommended six months?

    I were to place a wet painting and/or a wet palette in a carbon dioxide or argon rich tent would I be able to postpone the formation of a drying skin, thereby extending the open time of the paint and canvas?

    Thanks Denis


  • Question asked 2017-08-03 21:34:36 ... Most recent comment 2017-08-04 12:13:01
    Oil Paint Sizes and Adhesives
    Question

    ​How archival is oil painting on birch panels that are sized with a few coats of shellac? The panels are only 1/8inch thin and prone to warping as they are not cradled. Would shellac be alright to oil paint directly on top of if they were 1/4inch and cradled? If shellac isn't archival can you recommend a way to prepare panels that gives a similar feel when applying paint?

  • Question asked 2017-08-02 22:36:10 ... Most recent comment 2017-08-03 20:53:52
    Industrial and Non-Traditional Products
    Question

    ​I want to paint directly on Aluminum with Acrylic paint and also collage on the aluminum using Acrylic Matt Medium as the adhesive. I was told I should use a degreaser on the aluminum and than could directly paint on it. Would a solution of distilled vinegar, baking soda and water work as the degreaser. Do you have any other recommendations. I want the aluminum in places to show throught so I don't want to prime the aluminum.

  • Question asked 2017-08-02 19:22:20 ... Most recent comment 2017-08-03 20:46:07
    Oil Paint Solvents and Thinners Paint Mediums Drying Oils
    Question

    I am an oil painter and replaced Gamsol with oil of spike lavender about a year ago in an effort to make my studio less toxic. I've been mixing about one part spike lavender to two parts walnut oil for my medium, and adding a bit more walnut oil to the mix for subsequent layers. (I clean up with saflower oil and Murphy's oil soap). This medium has been working fairly working well but I've had a hard time finding concrete information on the stability of spike lavender in paintings over time. I found a post on this forum that explained "Painting with large amounts of any essential oil can lead to the formation of a weakened paint film." I was wondering if anyone could please elaborate on this? For instance, what would a safe amount of spike lavender be? Further, I know that walnut oil forms a less ideal film than linseed oil, but I prefer it for its less-yellowing nature over time. Are there conservation concerns about using walnut oil and spike lavender in conjunction?

  • Question asked 2017-08-03 10:55:12 ... Most recent comment 2017-08-03 12:29:42
    Oil Paint Scientific Analysis Varnishes Paint Additives Paint Mediums Art Conservation Topics
    Question

    ​I know that some varnishes such as Gamblin's GamVar and Golden MSA varnish have UV protection due to ultraviolet light stabilizer and filters. I presume that these are close to being transparent as it's used in a very thin layer of varnish.

    Do you know of any process or product where similar light stabilizers and filters can be added to the oil paint itself via additions to a medium? Would this compromise the paint film? I was wondering if it would work to increase the lightfastness of the pigments and potentially could be present in greater concentrations than in varnish?

  • Question asked 2017-07-29 02:22:43 ... Most recent comment 2017-07-30 13:22:28
    Varnishes Industrial and Non-Traditional Products
    Question

    ​I am interested in exploring the full range of sheen that can be obtained in art, from the mattest to the glossiest. I am painting on Dibond panels (currently with acrylics, but occasionally with oils). I am not particularly impressed by the usual gloss look of fine art varnishes. More and more I'm interested in this type of finish:

    https://www.youtube.com/watch?v=K0pXjV4zGDM

    But it seems that the best results are achieved by polishing with buffing compounds on top of 'super coating' varnishes (usually alkyd based?). The manufacturers claim that these super coatings are non-yellowing and flexible, chemically resistant etc. Here is an article:
    http://www.woodworkingnetwork.com/articles/tips_for_using_super_coatings_127702208.html

    I am aware that these varnishes will eventually scratch (or age) during the lifetime of a painting.
    How can I achieve the highest possible gloss while still keeping up with the good practices of painting?
    Are there any removable fine art varnishes that can be buffed up to this level of finish?

    Cheers

  • Question asked 2017-07-28 09:38:44 ... Most recent comment 2017-07-28 12:31:03
    Drawing Materials Grounds / Priming
    Question

    ​Hi,

    A friend who is an experienced metalpoint artist recommends Golden's Pastel Ground for metalpoint; he says it has more tooth, he's able to get richer darks, and thus prefers it to Golden's Silverpoint Ground.  I got some of the Pastel Ground to try and discovered it's transparent, not opaque - and I need opacity to cover the MDF support I'm applying the ground too.  Any considerations to combining equal parts Golden's Pastel Ground with either Golden's Sandable Hard Gesso, or Golden's Absorbent Gesso (both of which work well for silverpoint and I already have in the studio)? 

    I don't have Golden's Silverpoint Ground on hand, but may order to experiment with if it's sandable - can you get a readily sandable, perfectly smooth surface with that ground?

    Thanks,

    Koo Schadler

     

  • Question asked 2017-07-25 16:30:58 ... Most recent comment 2017-07-27 22:48:04
    Oil Paint
    Question

    ​Hello,

    I am working on some portraits where the accuracy of value is critical and for areas that have sunken in from previous sessions I have been oiling out by rubbing thin layers of linseed oil (I've tried raw, stand, refined, 50/50 linseed and Gamsol OMS) on the surface. I have read mixed reviews of putting an isolated layer of oil into the paint film structure, for fear of disrupting fat over lean, cracking, darkening, etc. It seems retouch varnish has similar concerns.

    Is this oiling out (or painting into a couch) a problematic practice, and if so, how can the color be restored in a more structural way while working? 

    Are there best practices to oiling out? Oil, technique ,etc.

    Grazie Mille

  • Question asked 2017-07-20 15:38:21 ... Most recent comment 2017-07-23 16:04:58
    Oil Paint
    Question

    ​Greetings,

    I came back to the studio today and some piles mixed tube colors of oil paint from yesterday have now 'skinned over,' though the paint below stil seems fresh and usable.

    Is it problematic to use this paint, removing the dried skin, and painting with as usual? 

    Does the paint below have the same properties as paint left on the palette without the skinning, or has the complexity of the oxidation of the oil now made this paint different somehow and less desirable, perhpas more lean...?

    Gracias


  • Question asked 2017-07-19 16:31:15 ... Most recent comment 2017-07-20 19:15:29
    Watercolor Ink Gouache Flexible Supports
    Question
    I would like to protect ink and watercolor paintings on thin rice paper (unsized Xuan paper) by mounting them. They are quite big - around 100x70 cm each. I'm not sure how to proceed with this - should I dry or wet mount? Is it better to use thicker paper (bristol) as backing, or maybe a fabric like polyester? Would methylcellulose glue be sufficient?
  • Question asked 2017-07-19 19:16:11 ... Most recent comment 2017-07-19 20:24:46
    Grounds / Priming Oil Paint Flexible Supports
    Question

    ​Hi. I have a roll of oil primed linen from a company that describe their production process like this -  "For an ‘oil canvas’, zinc white is used as the primer, bound with linseed oil."

    Given the issues associated with the use of Zinc what are your recommendations - use this product or not?

    Many thanks.

  • Question asked 2017-07-15 13:53:10 ... Most recent comment 2017-07-19 11:45:11
    Egg Tempera Grounds / Priming Oil Paint Technical Art History
    Question

    Oil paints become increasingly transparent with age, due to changes in the refractive index of the binder, I believe.  For this reason, I've seen white grounds recommended as generally preferable to dark toned grounds (so as the paint grows more transparent, the light values in a painting aren't darkened by an underlying dark ground).  A few questions relative to this:

    1.  I believe the same is true for egg tempera paints - they become more transparent with age, yes?  

    2. Is it true of other paints?

    3. Is there concern or evidence to show that the converse is true;  that paintings on white grounds, as they age, lose some of the depth in their dark values (because the white ground shows through the increasingly transparent paint), to the detriment of the painting's value pattern?

    Thanks,

    Koo Schadler

  • Question asked 2017-07-14 13:05:41 ... Most recent comment 2017-07-14 19:13:05
    Flexible Supports Industrial and Non-Traditional Products Scientific Analysis
    Question

    ​Hello,

    Does anyone know of or have access to tests of flexible supports that include synthetic canvases? I clearly remember mention of an ongoing test comparing flexible supports on the no longer available AMIEN forums. The thread was a discussion on synthetic canvas and indicated that at least some synthetics greatly out-performed traditional canvas.

    I was so impressed that I eventually asked a textile designer for help producing a heavier-weight synthetic canvas that is wider and more affordable than I could find on my own. I've been working with this canvas for a few years, and recently interviewed the designer (Scott Bodenner) about the project. Talking to someone with a textile industry point of view was fascinating. There are differences in how testing is done for commercial textiles and also a concern for recycling and sustainability that I don't encounter much in reading about artist materials. The interview is posted on my own website at: 

    http://sloweye.net/scott-bodenner-recycled-synthetic-canvas/

    But I'd still really like to know how the test I saw mentioned on AMIEN turned out! Fingers crossed someone remembers what that was...

  • Question asked 2017-07-12 16:12:41 ... Most recent comment 2017-07-14 16:35:36
    Oil Paint
    Question

    What is the opinion on the usage of non-traditional drying oils? I have read about the usage of candlenut, perilla or tung oil in some art works, but there's not much I could find in terms of conservation issues regarding these.

  • Question asked 2017-07-11 17:21:59 ... Most recent comment 2017-07-14 12:36:41
    Oil Paint Solvents and Thinners Paint Additives
    Question

    ​Hola Mitra,

    I have been looking for more information about the safe or recommended amount acceptable to thin oil paint with solvent. I'm using tube paint and odorless mineral spirits. In the past I have sketched in a drawing on top of the ground of acrylic gesso on canvas with a brown earth and liberally diluted the paint near watercolor consistency so that it really flows. (I then add straight tube paint or progressively less oms with the paint, and sometimes fatter glazes on that.) But recently I've read oil paint shouldn't be thinned beyond a whole cream milk consistency to avoid problems such as future delamination and breaking down the oil paint film (and polymers?). Personally I haven't seen problems in my paint films, not yet anyway, though sometimes it seems some tinted solvent has seeped through and is visible on the reverse side of the painting- like some stained spots...

    More information surrounding this topic would be appreciated.

    Specifically, are there established guidelines for how much oil paint can be thinned with oms?  Is oms even a good diluent for oil paint, or are other solvents preferred (Essential Oils, Turps, mediums with stand oil, alkyds) especially in this lower layers? If this thinned layer leaves the ground with much tooth available for thicker paint to adhere to, would delamination problems persist. And I've come across the idea that oms evaporates fully and thus doesn't alter the lean-ness of the paint once it's gone, is this true?

    Thank you for any time you can space on this topic!


  • Question asked 2017-07-03 13:45:56 ... Most recent comment 2017-07-08 18:20:28
    Oil Paint Paint Additives
    Question

    ​Greetings,

    I would like to apply oil paint on canvas (large scale) in thick smears similar to Richter, but am looking for some insight into the best practices for this approach to avoid problems such as wrinkling, cracking, excessive drying times, etc. 

    Do we know if he is altering his paint from tube consistency? Would this be recommended and if so what additives/ amendments? 

    (Implict question: I know you recommend rigid supports for thick paint, but is there a practical solution for large paintings, say 4 x 6 feet?)

    Mille Grazie

  • Question asked 2017-07-03 12:49:24 ... Most recent comment 2017-07-08 18:11:40
    Sizes and Adhesives Rigid Supports Industrial and Non-Traditional Products
    Question

    "Artist quality" PVAs and other such sizing products are too expensive and hard to obtain for me. There is no BEVA/MSA Varnish/B-I-N either. What I can obtain are various acrylic primers made for porous surfaces, regular PVA glue (the manufacturer states that the pH is 6-7), as well as methylcellulose wallpaper glue and boiled linseed oil.

    The acrylic primers are basically watery liquids that smell just like acrylic mediums. Their manufacturers typically state that they are made from acrylic dispersions, and that they are made for priming porous surfaces, unifying them and decreasing their absorbency - some add that they still let water vapor pass through after drying.

    I was wondering which one of these would work the best for sizing before laying down a layer of (artist quality this time) acrylic ground. The acrylic primers seem to be the best option, but I read differing opinions about the properties of hardware store products. I know methylcellulose is a good size, but I don't know how well it would perform on surfaces like hardboards and fiberboards.

    As for the boiled linseed oil, I'm not sure whether it wouldn't reduce the adhesion of the acrylic ground.

    I'm open to suggestions if there's something else I could try.

  • Question asked 2017-07-06 03:10:50 ... Most recent comment 2017-07-06 18:28:16
    Oil Paint
    Question

    ​Greetings,

    I've recently read on another forum (NP) a great article that said oil paintings when possible should be made by using the most opaque colors in the lower layers and layered up toward more transparent pigments. However, it seems many paintings from the past used brown grounds or thinned brown (umber or sienna?) as a drawing color in the lower paint layer. (Another recommendation that was surprising to read was to paint from light to dark, and thus moving from light and opaque lower to dark and transparent upper layers.) 

    Which pigments do you recommend "blocking in" a drawing in the underpainting, and is the opaque to transparent layering order generally accepted?

    Is my read of many historical painting practice off, or do we just understand the chemistry better and have new best practices?

    Thank You for this amazing resource!

  • Question asked 2017-06-29 05:56:17 ... Most recent comment 2017-06-30 08:26:07
    Health and Safety
    Question

    Looking through Safety Data Sheets for various art supplies, I have noticed a strange discrepancy between the information provided by various manufacturers. A good example is "naphtha (petroleum), hydrotreated heavy", with CAS number 64742-48-9. A basic search through toxicology databases shows that it is considered both mutagenic and possibly carcinogenic (1B), with numerous reported adverse health effects (https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/details/115111). Yet, looking at the SDS for Gamblin's Galkyd mediums (https://www.gamblincolors.com/wp-content/uploads/2016/05/SDS-Galkyd-Galkyd-Slow-Dry.pdf), there seems to be only information about them being flammable, a skin irritant, toxic to aquatic life and causing drowsiness. My question is then: which information should I go by? Am I risking cancer or chronic painter's syndrome by using these mediums? It seems like the exact same substance that, in other manufacturers' products, causes cancer is safe here. How is that possible?

  • Question asked 2017-06-29 10:42:26 ... Most recent comment 2017-06-30 07:13:07
    Egg Tempera Flexible Supports Grounds / Priming Scientific Analysis Technical Art History
    Question

    Yesterday I went to the Boston Museum of Fine Arts to see the show of Botticelli and his contemporaries.  It's a beautiful collection of work, and I marvel that the museum was able to get 500 year old paintings from Italy to Boston - a real treat. Given that the 15th c. was a transitional time for paint (egg tempera to oil) I was curious to see the labeling.  Most pieces were simply "tempera on panel"; several were "tempera on canvas"; a few were either "tempera and oil" or "oil". 

    I wish labeling in museums was more consistent and specific.  However I appreciate that museums are generally challenged by finances, resources, time.  My guess is that different museums have different approaches and philosophies to analyzing mediums (it's not necessarily every museum's priority); a lender has to accept what the lendee says about a piece; there is not enough money for conservators to definitively analyze ever work in a collection; it's still difficult to say for sure what a 500 year old painting is composed of (especially if mediums are mixed, i.e. tempera and oil).  My questions are...

    1. Any other thoughts on way medium labeling can be vague?  

    2.  Some works (as evidenced by the brushwork and finish) were clearly egg tempera.   Other works looked so rich and painterly it was hard to believe they were just tempera; hints of tempera brushstroke were evident, but other areas were smoothly and thickly painted. Is it possible there’s some oil paint in the mix and the works  aren't accurately labeled?  Or would the varnish that was apparent on most of the paintings be sufficient to give these egg temperas an oil look?  Or maybe it's that the Renaissance masters were capable of a much greater range of effects in tempera than they’re generally credited with (i.e. they did more than just hatchstroke, as is often claimed)?  I’m trying to better understand what’s going on in these “quintessentially egg tempera" masterpieces (that, in fact, often don’t look like “quintessential” egg tempera). 

    3.  A traditional chalk and glue ground lacks flexibility, and egg tempera paint become brittle with age – so I don’t understood how a 500 year-old egg tempera survives on canvas (i.e. Botticelli’s Birth of Venus).  Could there be some oil emulsified into the ground or paint?  I know the Birth of Venus is painted thinly (you can practically see the weave of the canvas in parts, it seems to me) – would the thinness of the paint layers be sufficient to deal with the flexibility in canvas?  Or are most temperas on canvas backed by a solid panel (tho’ I don’t think the Birth of Venus is….).  In short, how to explain egg tempera on canvas?

    4.  As mentioned, much (most?) of the work appeared varnished.  Is there a way to determine which of the varnishes are original, which added in later centuries?  How do conservators address a Renaissance painting that enters their collection and has a varnish?

    Thanks for your help in better understanding this wonderful but complex period in art history.  

    Koo Schadler

  • Question asked 2017-06-28 20:07:54 ... Most recent comment 2017-06-28 21:48:42
    Oil Paint Varnishes
    Question

    ​Hi everyone,

    I have a problem and hope to get some advice from the collective wisdom here. I finished a painting about 2 months ago, and let it sit for a few weeks before spraying it with retouch varnish so that I could refresh the colours and get a decent photo. I then moved the painting into a spare room that is seldom used, and left it there to cure. Today I discovered that my husband went into the room a few days ago and moved the painting . . . he leaned it *face down* against a sofa. When I moved it today, it actually made a faint sound as I pulled it away from the sofa, something like pulling low-tack tape off a wall. :( It looks now like there is a spot where the paint looks a bit flat, and otherwise there is lint/dust that I cannot brush off with my fingers. Do I need to use mineral spirits and strip off the retouch? Or is there something else that I can use to clean the surface without disturbing the retouch? Thoughts? Advice?

    BTW, in case it helps: I painted this one in layers, using a thin layer oleogel as a couch between layers. The retouch varnish is Winsor & Newton, because I've found that other brands (particularly Krylon) don't get along well with the oleogel.

    Thanks in advance.

     

    Jennifer

  • Question asked 2017-06-26 03:39:20 ... Most recent comment 2017-06-28 18:42:30
    Oil Paint Pigments Scientific Analysis
    Question

    ​Hello,

    I'm interested in using PBr33 due to it's very dark opaque nature.. It's used by Sennelier and Schmincke in a few of their oil paints. However as it's made using Zinc I'm just concerned it could make the resulting paint film brittle in the same way zinc white can.

    But I don't know if the combination with the iron and chromite would avoid this issue.

    Does anyone have any opinions on this?

  • Question asked 2017-06-05 05:50:42 ... Most recent comment 2017-06-28 17:32:02
    Rigid Supports Oil Paint Acrylic Sizes and Adhesives
    Question

    I have recently read that the outgassing of formaldehyde from urea-formaldehyde used to manufacture HDF and MDF is a problem when it comes to conservation, since it can influence the acidity of both the work and the environment, leading ​to possible degradation of the artwork. I also read (Getty's "Facing Challenges of Panel Paintings Conservation", part 3 by Paul van Duin) that urea-formaldehyde itself degrades over time and the author estimates its longevity (when protected from light) to be a couple of decades. In light of this, I was wondering if hardboard (wet process board) wouldn't be a better choice, since it doesn't contain UF?

    On the other hand, I used to coat the panels I paint on with a water solution of PVA with a pH of 6-7 (according to manufacturer), and I read that PVA can be a source of acetic acid, but I'm not sure if this is relevant.

  • Question asked 2017-06-28 10:17:57 ... Most recent comment 2017-06-28 15:18:39
    Flexible Supports
    Question

    ​how best to repair torn painting on canvas

  • Question asked 2017-06-25 01:04:07 ... Most recent comment 2017-06-26 18:58:10
    Sizes and Adhesives Rigid Supports
    Question

    ​I am wondering if it is okay to use a heat press to mount linen to a panel using Beva 371 film after the painting has been completed. I like to glue it afterwards because not every painting works out, and I'd like only glue the ones that I (or a buyer) determines a success. I heat it at 150 degrees for 6 minutes twice, once to attatch the glue film to the board, and a second time to adhere the linen to it.  I am painting with oil paints using Gamsol and linseed oil as a medium, and painting without a lot of texture (which I have found that the heat press flattens), and gluing them to boards of MDF or hardboard. I have not noticed any issues, but am concerned that somewhere down the line the fact that the painting has been heated up might pose a problem. Additionally, I am wondering if I need to seal or size the support before I adhere the linen to it.  Thanks so much. This is a great forum. 

  • Question asked 2017-06-25 21:15:17 ... Most recent comment 2017-06-25 21:53:43
    Rigid Supports
    Question

    ​It is recommended to size and/or prime a wood panel (eg. birch plywood) adequately to prevent oil penetration. What exacly would happen to the panel if a substantial amount of oil was absorbed into it due to inadequate or no panel preparation (bare wood).  Would the acid in the oil damage the wood?

  • Question asked 2017-06-18 13:00:16 ... Most recent comment 2017-06-19 10:30:50
    Gilding
    Question

    ​Best recommendations for an oil mordant for use to gild an icon?

  • Question asked 2017-06-09 16:12:21 ... Most recent comment 2017-06-15 20:32:09
    Sizes and Adhesives Paint Mediums Oil Paint Drying Oils
    Question

    I’m hoping someone can help me with two issues I’m having with painting:

    1. I am using oil sticks to paint on muslin fabric or even a polyester for my canvas, and I'm trying to see if there is a way to avoid the fabric from breaking down over time because of the oil based paint. Because of the type of painting I am doing, I wet the canvas first with a spray bottle and therefore I can’t seize the canvas prior to applying the paint to the canvas using traditional methods such as jesso. 
    2. Because I am applying the oil sticks to a damp fabric, the drying time is extended significantly.  

    Any advicde would be greatly appreciated. Than you.

  • Question asked 2017-06-02 14:48:33 ... Most recent comment 2017-06-15 16:36:18
    Paint Additives Oil Paint
    Question

    ​Greetings,

    I have been trying to modify oil paint for textural effect and my goal is to make the paint thick sticky and ropey/ stringy. Auerbach sometimes seems to have gotten a similar paint quality where the rheology of the paint is highly thixotropic alla Lead White. I've also been thinking of the quality of silicon caulk as the texture I am after. 

    I have expeirmented with adding stand oil, dammar, clay made into paste, alkyd, etc but these tend to 'shorten' the oil, lowering the viscocity (with the exception of the clay). My next step is to see what marble or glass powder does. I have a (Daniel Smith) tube of transparent blender made with alumina hydrate that is perhaps the closest I've found for the texture I am after.

    Any suggetions for this type if paint modification would be helpful. 


    Thank you!

  • Question asked 2017-06-14 13:40:09 ... Most recent comment 2017-06-14 23:20:40
    Oil Paint
    Question

    ​I used an aluminum panel for a painting support for an oil painting for the first time. A month after the painting dried to the touch, I wrapped it unvarnished  in acid-free tissue, wrapped in foam, then in bubble wrap in a cardboard box on a flight. It was wrapped this way for about 1 week. When I hung it for my exhibition I noticed strange splotches that resemble mold. They are not uniform and were not there before packing. The aluminum was purchased at an art store with plastic vacuum sealed to both sides. I took off the plastic and primed it with 4-6 layers of Grumbacher Gesso for oils, sanding between each layer. I used Rublev Raw French Umber thinned with Rublesol for the underpainting, followed by Rublev paint straight from the tube with no medium added. The main colors I used were Lamp Black and Lead white. Is there some reason you can imagine that would cause this type of reaction? Will it go away when I varnish? I've read that using denatured alcohol and lead primer would help prevent this in the future (whatever this is), but wouldn't so many layers of gesso be good enough? Thank you!

  • Question asked 2017-06-09 23:14:16 ... Most recent comment 2017-06-10 09:16:00
    Varnishes Technical Art History
    Question

    ​Hello. I'm not sure if this question really belongs with the Varnish questions, but I couldn't find any better matches. I was reading an abstract from the journal Nature in which some Tate Modern conservators described their research into Rothko murals.* In their words, "Rothko [...] applied phenol formaldehyde to prevent layers from blending into one another." I imagine this working something like workable fixative between paint layers. Is that correct? Are there other documented uses of phenol formaldehyde for this purpose? How would the use of it affect paint adhesion in layers above? 

    I'm not aware of too many companies selling anything like this, although Lefranc & Bourgeois offers "Harlem Duroziez drying medium"** which they say contains phenol formaldehyd resin. Are there other manufacturers which offer it in a liquid or spray form?

    * https://www.nature.com/nature/journal/v456/n7221/full/456447a.html

    ** http://www.lefranc-bourgeois.com/beaux-arts/telechargement/A_TELPDF_2010092817171362.PDF

  • Question asked 2017-06-07 13:25:41 ... Most recent comment 2017-06-09 12:31:01
    Industrial and Non-Traditional Products
    Question

    ​I am looking for an adhesive to adhere tar paper to a masonite panel. Any suggestions? Thank You!

  • Question asked 2017-06-07 18:20:51 ... Most recent comment 2017-06-08 23:23:36
    Rigid Supports Sizes and Adhesives
    Question

    I want to attach unprimed linen to Gessobord and then prime with lead oil ground. I want to use cradled and sealed Gessobord to skip steps of sealing/cradling even though a bit more expensive. My question is which adhesive is better – Lineco Neutral PH Adhesive or Beva Adhesive? Note: I don't want to deal with the Beva in a film form. it sounds too tricky. Thank you for this site! 

  • Question asked 2017-06-07 10:57:25 ... Most recent comment 2017-06-07 11:25:28
    Health and Safety Oil Paint Paint Mediums
    Question

    I sometimes use Black Oil ( linseed oil boiled with lead) to speed up the drying time of the oil paints. Once the paint is dry if you sand or scrape the surface does the presence of Black Oil in the paint present a health issue with the airborne particles ?

    Many thanks

    Jim G

  • Question asked 2017-05-31 11:56:54 ... Most recent comment 2017-06-01 22:19:28
    Acrylic Paint Additives Paint Mediums
    Question

    My acrylic paintings sometimes show a noticeable amount of color lifting (particularly when using a relatively large amount of retarder) - rubbing a wet cotton swab causes a small amount of color to be left on the cotton. There seem to be no major adhesion failures, even in cases where I might have used more than the recommended amount of retarder. I was wondering if I should secure such layers of paint by brushing a layer of medium on top? I remember reading that it's generally a good idea to provide such a protective layer in practically all cases.

    And in case this ever happens, what would be the best course of action if the paint remained "tacky" due to too much retarder?

  • Question asked 2017-05-26 18:39:48 ... Most recent comment 2017-05-26 19:27:30
    Grounds / Priming Acrylic Oil Paint
    Question

    ​I know that the sensitivity that acrylic polymer films have to solvents presents challenges when it comes to the cleaning of acrylic paintings. Is there a similar concern for oil paintings executed on an acrylic ground? Or do the layers of oil paint (assuming that the ground is well covered) provide an adequate barrier against the action of sovents used in cleaning?

    -Ben

  • Question asked 2017-05-14 17:00:13 ... Most recent comment 2017-05-21 19:31:33
    Drawing Materials Grounds / Priming Egg Tempera
    Question

    I sometime expose my metal point drawings to sulphur (by placing them under a "tent" alongside an open jar of liver of sulphur) to speed up the oxidation and darkening of the drawing.  Does exposure to sulphur cause any detrimental affects to the materials of a metalpoint drawing (to either a paper or wood-based panel support; or to an acrylic or traditional gesso ground)?  Are there other recommended ways to speed up oxidation?  I had a cohort once tell me he sips whiskey while drawing and blows on his images - any truth to his claim that this speeds oxidation?  

    By the way, which is correct: metalpoint?

    Koo Schadler

  • Question asked 2017-05-14 17:05:44 ... Most recent comment 2017-05-21 02:21:32
    Rigid Supports Oil Paint Flexible Supports
    Question

    ​I know that historically, linen with a close, tight weave was prefered for its strength. If one is mounting (pre-primed) linen to a rigid panel rather than stretching it, is there any particular reason to worry about using a loose-weave linen similar to what would have been called an "Étude" canvas in the 19th century? "Loose" meaning that there is enough space between the yarns that you can see tiny squares of the ground from the back of the linen. 

    ArtFix L21C and Fredrix Paris #908 HP are modern examples of this type of linen. I like the texture a lot on both, but am not sure if the loose weave is likely to be an issue in mounted linen. 

  • Question asked 2017-05-02 07:32:24 ... Most recent comment 2017-05-17 23:25:55
    Sizes and Adhesives Studio Tools and Tips Oil Paint Flexible Supports
    Question

    ​I like to use Beva 371 film to mount oil-primed linen to tempered hardboard. It usually works great, but sometimes I'll have a spot or two right on the edge of the panel where the linen just doesn't want to adhere, and remains loose. Going back over these spots with my tacking iron never seems to help. 

    I always adhere the Beva film to the panel first, and then mount the linen. Would it be better to start by attaching the film to the linen? Or, could I take out some "insurance" by attaching a layer of film to *both* the linen and the panel? 





  • Question asked 2017-05-09 09:23:46 ... Most recent comment 2017-05-15 11:04:12
    Oil Paint
    Question

    ​There has been some discussion on another forum regarding colour matching for touch-ups to sections of oil paintings. The problems seem to be related to adding mediums - especially mediums containing solvents (such as alkyd mediums).  Colours sometimes dry lighter or darker than expected - depending on the medium used and whether medium was added before or after colour matching. I was wondering if there are any pointers from how conservators handle matching colours for inpainting that would help artists in matching colours for tehri own touch-ups.  Do you use just straight paint? Add medium before or after mixing the right colour?  What medium do typically you use? Any insights into your typical in-painting process would be helpful.

  • Question asked 2017-05-08 10:26:21 ... Most recent comment 2017-05-08 11:11:24
    Oil Paint Drying Oils
    Question

    ​Is it OK to put an oil painting out in the sun to dry to speed up drying?

  • Question asked 2017-05-02 13:49:43 ... Most recent comment 2017-05-02 21:04:28
    Question

    ​Hi.  I'm an oil painter considering using KILZ 2, (latex water-based primer, sealer and stain blocker composed of  Titanium dioxide, Nepheline Syenite, Limestone) as a sealer for maple panels.  I will use 4 or more coats of acrylic gesso (either Golden or Art Board) after the KILZ.  I hear that KILZ is a good seal for panels but also know that industrial grade materials aren't always tested/recommended if the intention is to build an archival surface.  Do you recommend KILZ or should I stick with GAC 100?  Thank you. 

  • Question asked 2017-04-21 23:45:13 ... Most recent comment 2017-05-02 07:24:45
    Rigid Supports
    Question

    ​Dear Moderators


    Thank you for this wonderful website. So glad to see AMIEN has a successor.

    I plan to paint on some RSG sized canvas and then (if the painting works out) to glue it to a rigid support. I had hoped to use my untempered Masonite as substrate to glue the textile to but recently read here that tempered is far better (however I don't hold out much hope of getting that product here in Australia). I am very much aware of all the disadvantages of using RSG (have been reading about them for decades) but I strongly prefer the working qualities it imparts to the surface I paint on. Also I understand that RSG is much less problematic when used on a rigid support, if all precautions are taken (such as sizing and priming both sides and also varnishing both sides at the proper time etc). I had planned to just go ahead and glue the linen to the Masonite and then do the painting (much more straightforward) rather than size a stretched canvas, paint on it and then glue it on to the Masonite. However I can't do this till I find a source of tempered Masonite. In the meantime I want to paint. My question is: is it unwise to use hot RSG to glue a finished painting to a substrate? Is it likely that the hot glue would damage the painting? 

  • Question asked 2017-04-29 02:59:41 ... Most recent comment 2017-05-02 07:21:30
    Art Conservation Topics Oil Paint Scientific Analysis Technical Art History
    Question

    ​Will all oil paintings eventually crack, even if painted on a rigid surface with a good oil binder in the correct ratio and avoiding pigments like Zinc?

    Do these good practices only extend the time it takes before cracking occurs?

  • Question asked 2017-04-20 12:46:55 ... Most recent comment 2017-05-01 14:21:42
    Acrylic Grounds / Priming Rigid Supports Flexible Supports Art Conservation Topics
    Question

    ​Debating whether to use pigmented Shellac BIN or GAC 100 as sealer.  From what I've been told, Shellac BIN is a sealer, GAC 100 is not.  (regular Shellac can dissolve acrylic paint due to alkaline sensitivity to ammonia but Shellac BIN seems to be ok)

    GAC 100 reduces SID, but so can Shellac BIN.  

    It seems like Shellac BIN is winning out here... I plan to put a couple layers of Gesso on top of either Shellac BIN or GAC 100 before painting of course.  If Shellac can do what GAC 100 can do but it is a true sealer wouldn't Shellac BIN be a better choice?  

    Regarding WARPING: Someone told me that shellac also can prevent warping due to blocking moisture.. is this true?

    I'd like to eventually work bigger than 48" at some point and use the thinnest plywood possible (prob birch) to keep it light and of course cradle and brace it with supports.  But what are your thoughts as to warping at this size?  Would getting 1/4" be too thin?  What if I put 3 layers of Shellac BIN?

  • Question asked 2017-04-30 16:40:25 ... Most recent comment 2017-05-01 09:16:29
    Varnishes
    Question

    ​On Dec 2015 I finished a painting which later I varnished with Gumbacher Matte Dammar in Spray (4 months later).

    Last October the owner asked me to give it another coat of varnished (which I didn't know is not recommended).  Then I gave a coat with a cheap liquid matte varnish becayse I didn't find a good brand).  While I was applying it, the painting started to dilute a little bit.  I don't know if that was due the thin sprayed former coat or another reason. I could handle to eliminate marks and had a very good finish. However spots as if sinking in are appearing now.

    I have to fix it, but I don't know how.  I've never removed varnish before, so I'm afraid of doing so. Some solutions come to my mind.

    1. Varnish again (I know it's not good to use gloss over matte so I thin ther painting could  maybe stand another matte coat)

    2. Buff with cold wax to get an even surface.

  • Question asked 2017-04-28 07:57:35 ... Most recent comment 2017-04-28 22:18:57
    Varnishes Oil Paint
    Question

    ​Does anyone know if MS2A resin is still being produced? I've been looking for a source online, but haven't had any luck finding one.

  • Question asked 2017-04-27 07:01:42 ... Most recent comment 2017-04-28 21:17:05
    Rigid Supports
    Question

    ​Dear moderator


    Could you please advise how one might go about removing a painting done on linen from a panel (to which it has been adhered using acrylic medium) in the event that the panel has proven to be an unsuitable support or become damaged in some way? Or simply because the painting done originally didn't work out and one wants to glue a new piece of linen to the panel? I have tried removing linen from panel under the latter circumstances (when the painting didn't work out and was destined for the rubbish bin) , simply by pulling it off but found it virtually impossible. What solvents might a conservator use to achieve detachment in the event of a painting that needs to be saved?

  • Question asked 2017-04-16 16:43:34 ... Most recent comment 2017-04-24 14:30:11
    Oil Paint Art Conservation Topics
    Question

    ​Hello, 

       Someone on another forum (who lives in a warm climate) recently mentioned deliberately placing paintings in the sun to speed drying. They do it  both when finished and between layers. They mentioned that paint dried to the touch in a matter of hours. It made me curious. It sound convenient but I suspect that there are some inherent dangers to this approach.  I looked through the resource documents and there were hints that it was not a best pratcice but I couldn't find any explicit information. Any insights into potential problems with this practice?

       Thanks in advance.

  • Question asked 2017-04-20 20:05:55 ... Most recent comment 2017-04-24 11:01:00
    Acrylic Watercolor Gouache Egg Tempera
    Question

    ​From what I know, there is no limit to how much watercolors can be diluted when painted on paper. I was wondering if the same can be said of all the other water-soluble paints. Is it okay (in terms of durability of the finished work) to dilute:

    1. Acrylics
    2. Gouache
    3. Tempera (egg and non-egg)
    4. Inks

    as much as one wants if painting on an absorbent support, like paper? I read that the absorbency of the fibers ensures that the pigments are trapped within the piper, so there should be no conservation issue in that regard. Is that true?

    Also, should such works be varnished, and if so - with what?

  • Question asked 2017-04-09 12:32:20 ... Most recent comment 2017-04-11 20:18:00
    Acrylic Paint Additives Art Conservation Topics
    Question

    I know that acrylics can be made less durable by adding too much water or extender/retarder to them. I was wondering if this could be remedied later on by either

    a) coating the weakened layer with medium

    b) overpainting the weakened layer with acrylics that haven't been overextended or oils

    ?

    Would sealing the overextended layer with medium/paint have a similar protective effect as painting over tempera with oil?

  • Question asked 2017-04-09 11:54:22 ... Most recent comment 2017-04-11 18:23:00
    Rigid Supports
    Question

    ​I recently found online a kind of artist ACM panel with an anodized surface. The store that makes the panels claims the surface is porous enough to paint on directly with oils and acrylics, although I'd personally want to prime the panels first. Anodized aluminium as a painting support seems quite uncommon - however I did find at least one well-known artist, David Dunlop, who regularly uses it. And so I was wondering, are there any problems associated with priming then painting on anodized aluminium? As always, any advice would would be appreciated. Many thanks, J.

  • Question asked 2017-04-11 07:01:58 ... Most recent comment 2017-04-11 11:17:00
    Oil Paint
    Question

    Hello MITRA,

    On one of your resource handouts you say, "Some artists choose to place their paintings in direct sunlight for a certain period of time as UV light can break up some of the chemical bonds that are responsible for yellowing."  What length of time, more or less, is it suggested that an oil painting be exposed to sunlight to counteract yellowing?  Any caveats, besides being aware of fugitive pigments? 

    Thanks 

  • Question asked 2017-04-08 22:00:47 ... Most recent comment 2017-04-09 20:54:00
    Art Conservation Topics
    Question

    ​Hi there

    I've arrived here from the Wet Canvas forums, following a thread I was interested in, regarding damage to the acrylic "gesso" of a canvas, and subsequent oil strikethrough. Many respondents, in their answers, referred to the danger of "oil rotting the canvas", and indeed, searching this forum, found similar references. The problem I have is: I've never seen oil rotting a canvas. I've searched the internet of course, but may just be looking in the wrong places.

    I have some student canvases, they are about 25 years old, with paint stains on the side of the stretched canvas. There is no sign of degradation of the weave.

    oil-stains.jpg


    I have also read (I don't have a reference) that oil could be getting the blame from damage bry damp and mold in some cases. Is it possible that the fatty acids in Linseed Oil become effectively neutralized in the polymerization process, or simply locked up in the mass of fillers and pigment, and do little damage to the weave? I'm wondering what the evidence is to support the case for "oil rotting", and if there are photographs?


    Thanks!




  • Question asked 2017-04-09 18:53:54 ... Most recent comment 2017-04-09 19:36:00
    Flexible Supports Acrylic
    Question

    ​In the summer of 2016, I painted a 9-inch by 12-inch painting on 7/8-inch-deep Masterpiece "Vincent Sausalito" all-cotton stretched canvas. I added two coats of Golden acrylic gesso on top of the manufacturer's gesso, and then the painting was done in Golden acrylics. I framed it with a Nielsen aluminum canvas-depth sectional frame. It hung through the fall and winter in a winterized cottage in  northern Michigan, with the central heating system turned off.

    In early April of 2017 I found the painting in below freezing temps, in order to retrieve and varnish it. It apparently had undergone "planar" warping of the canvas surface, to use a term I've picked up on this forum. Over the course of a couple weeks in a separate year-round heated home, the warping has disappeared and the painting now looks fine. Ideally, I wanted to leave the painting year-round at the cottage, and am wondering if I should cut the painted canvas from the stretcher bars and glue it to 1/8-inch-thick Ampersand Hardbord with acrylic medium? First sizing the board on both faces and all four edges with acrylic medium. Was this sagging likely caused by the temperature change? Thanks for any insights and/or suggestions.

  • Question asked 2017-04-07 07:32:49 ... Most recent comment 2017-04-08 22:42:00
    Flexible Supports Grounds / Priming Art Conservation Topics
    Question

    ​Hi Mitra friends, 

    I originally posted this question on WetCanvas and they suggested I would ask it here to get a more in depth response. 

    I found many topics covering cracks in painting, but I promise this is not exactly related. 

    I spent many hours on a painting for which I stretched out the canvas myself, two layers of pva size and oil priming on top. 

    The painting itself has been built with many thin layers of oil paint with a little liquin to thin and accelerate drying of oils.

    Everything was going fine, but a few days back, the canvas fell from the easel and hit a chair corner. The fabric is absolutely fine, not even stretched out, but the area of the painting which hit the chair cracked a bit. 

    I was very upset and in hopes that the priming was intact, I tried to cover the crack with another layer of oil painting. 

    It seems to me that the sizing and priming were damaged due to the fall as the paint I applied afterwards went through and appeared on a cracking shape on the backside of the canvas. I'll try and post a picture with this for observation. 

    I was always told that oils will rot the canvas if it gets in contact with it (even though it might take years) but I wanted to know if there's any way I can avoid that from happening making the area "healthy" again? 

    Some people also said that the thin layers of oil will not damage the canvas if I apply acrylic primer on the back of the affected area? 

    I hope you'll be so kind to share any solid information you have on this issue?

    Thanks for reading! 

    CrackedPriming.JPG            

  • Question asked 2017-04-05 21:27:04 ... Most recent comment 2017-04-05 21:58:00
    Oil Paint Animal Glue Varnishes Flexible Supports
    Question

    ​I have had to withdraw a20170304_085913 - Copy.jpg painting for sale because of something that went wrong in its structure, sadly. This started on raw linen, rabbitskin glue (I don't use that anymore) I used oil priming- titanium with a heaping tablespoon of quality lead white paint and a small amount of quality turps. It dried several months and I used universal varnish on it. I don't heavy varnish, but a gallery in a different (dry) climate thought it needed more varnish. I bought the same brand etc and sent it to them and a respected artist with the same training added another coat. When I got the painting back, I loved it! It looked glassy and I preferred the look. However, this painting has always been the worst reactor to humidity changes of all my work. It's got crossbar supports, yes. It's now 13 years old and 2 years ago began to dimple.

  • Question asked 2017-04-05 04:29:19 ... Most recent comment 2017-04-05 15:56:00
    Flexible Supports Oil Paint
    Question

    ​Hello,  

    I have a few  questions about polyester canvas as a stretched support for oil paint.  I intend on buying a a roll of 100% polyester canvas from a very ubiquitous company.  It is "universally-primed".

    From what I've read, polyester canvas may be less susceptible to some of the humidity/moisture/movement related issues that linen and cotton enact upon an oil paint film.

    Then I read this entry by a moderator:

    Two things first. What is the attraction to polyester as a substrate for you and what type of paint are you planning to use on the polyester? I generally worry about the the overly flexible of polyester for any paint media other than acrylic dispersion paints. Let is know that and in the meantime I will ask some of the other moderators their opinions.

    Baade, Brian

    2016-12-13 21:23:01

    I intended to put a thin coat of lead white ground on top of the acrylic dispersion primer, then paint on it with oil paint.  I thought that if one were to forego panels, then this would be the "best practice" second choice ( with a vented matte- board backing).

    Am I wrong? Is linen or cotton a better, or indifferent, choice?

    I did email the company and they stated no zinc white is used in the priming.

    Thanks for your time and consideration.

    Kevin

  • Question asked 2017-02-24 09:55:55 ... Most recent comment 2017-04-05 10:28:00
    Art Conservation Topics Other Flexible Supports Industrial and Non-Traditional Products
    Question
    How can I make old newspapers less acid for use in my collages.
  • Question asked 2017-04-04 13:42:45 ... Most recent comment 2017-04-04 13:52:00
    Storage
    Question

    ​Do you have any suggestions on how to roll a 10' x 10' oil on muslin painting for storage? My friend acquired the large picture and cannot immediately stretch or hang it and was going to line with glassine and roll over plastic tubing, it had been folded in 10 inch sections. I thought the glassine was a bad idea and wasn't sure about plastic tubing.

  • Question asked 2017-03-31 03:29:55 ... Most recent comment 2017-04-03 16:50:00
    Acrylic Paint Mediums
    Question

    ​I am applying artist acrylic paint diluted approx. 10% with water onto a gesso prepared surface, with a small fine foam roller. The paint is foaming and although I can remedy this eventually, is there a way to prevent the initial foaming? Thanks.

  • Question asked 2017-03-28 08:55:03 ... Most recent comment 2017-04-01 22:02:00
    Acrylic
    Question

    For the underpainting on many of my acrylic paintings, I would like to use more opaque paints​ than most regular acrylic lines provide. 

    There are several products that I've come across -- mostly online but occasionally in the big art stores -- that are described sometimes as acrylic and sometimes as "vinyl." Examples include Lefranc & Bourgeois Flashe Vinyl Paint or Maimeri Polycolor Vinyl Paints. It's hard to tell from the online literature whether whatever it is that makes them "vinyl" would make them incompatible with "regular" acrylics.

    Are these safe to use: (1) as an underpainting for a more traditional acrylic paint (e.g., Golden Heavy Body); and, (2) inter-mixed with those same paints (e.g., to modify opacity)? I'm more interested in (1) but curious about (2).

    Thanks.

  • Question asked 2017-03-14 12:45:43 ... Most recent comment 2017-03-31 16:43:00
    Rigid Supports Sizes and Adhesives Oil Paint
    Question

    ​I'd like to know the accepted, archivally safe way to mount an oil painting created on paper (140 lb 100% cotton) onto a cradled birch panel. Specifically, how to seal the birch so acid cannot migrate to paper, and what no-acid glue to use for mounting.  

  • Question asked 2017-03-31 13:42:04 ... Most recent comment 2017-03-31 14:22:00
    Acrylic Sizes and Adhesives Flexible Supports Industrial and Non-Traditional Products
    Question
    When making things like collages, reliefs or textured paintings, would it be okay to use non-artist paper (for example, tissue paper) if it's first thoroughly coated with acrylic medium? I read that it can be used to preserve things like leaves, so I was wondering whether (aside from being an adhesive) it would stop paper that could be acidic from becoming brittle.

  • Question asked 2017-03-28 15:19:31 ... Most recent comment 2017-03-30 10:12:00
    Health and Safety Oil Paint Pigments
    Question

    ​I have a large oily waste can that contains rags contaminated with lead and mercury (vermilion) based pigments. In order to dispose of them, I will need to dump the waste into a large bag and bring it to a Hazardous waste disposal facility. The can I use has been sitting outside covered for around 6 months, and contains water for combustion concerns. Should I be concerned about any potential metabolic processes that may occur from mold or microbes growing within the rags that could potentially turn Mercuric Sulfide, into a more toxic form of mercury, or any other heavy metal based pigment? If so, what process should I take so that I can dispose of it safetly and not expose myself to these compounds. 

  • Question asked 2017-03-24 18:01:28 ... Most recent comment 2017-03-29 13:35:00
    Acrylic
    Question

    ​Hello! I observed a strange separation of paint/color after leaving the Golden Fluid Acrylic Iridescent Bronze (Fine) in a wet palette overnight. This could be just a colorant added to the mica? It was suggested by a supervisor that I contact you fine folks with this concern! Thank you!! (please see attached photo)

  • Question asked 2017-03-26 13:56:10 ... Most recent comment 2017-03-28 14:18:00
    Oil Paint
    Question

     My usual practice is to start with fresh paint every day - squeezing out just enough of the colours I think i will use for the section of the painting I am working on.  However, there has been discussion recently on several FaceBook forums about saving paint on the palette overnight or even longer - sometimes weeks. The two most common methods seem to be either a) putting the palette in a freezer or b) putting it in a sealed contained each night with a few drops of clove oil on a cloth in that container.  The freezer method seems to be prone to introducing condensation if not handled properly. Both methods will lead to using progressively dried paint over several days or longer. Are these approaches to reducing paint "wastage"  potentially problematic?

  • Question asked 2017-03-23 15:38:06 ... Most recent comment 2017-03-23 16:51:00
    Oil Paint
    Question

    ​Hello,

    I have a bit of dust dried into the top layer of an oil painting I'm working on and would like to lightly sand the surface, remove the dust and sanded particles, then continue with another layer of oil paint.  Should I be concerned with weaking the sublayer?  Thank you!  

  • Question asked 2017-02-11 12:21:09 ... Most recent comment 2017-03-20 16:56:00
    Grounds / Priming Industrial and Non-Traditional Products Rigid Supports Sizes and Adhesives
    Question
    As far as preparing rigid engineered wood surfaces for painting goes, the consensus seems to be that they should ideally be 1. cleaned 2. sanded 3. sized 4. primed. While various websites advise sanding according to preference between subsequent applications of ground to achieve a very smooth surface, what I usually found lacking is the advice of sanding before sizing.
    My questions are as follows:
    1. To clean the surface before sanding, I would use 95% ethanol applied with a rag/kitchen towel. Is this alright? Other options that come to mind are methylated spirits, mineral spirits or hardware store soap, all advertised as pre-paint cleaning agents, but I'm not sure whether they would make a difference and concerned about breathing in the methylated/mineral spirits fumes.
    2. There is generally no information about how hard the surfaces should be sanded - only that they should be sanded "lightly" so that they are lose gloss. The problem is that in order to really remove all visible gloss one has to sand much harder than lightly, so I sometimes have fibers sticking out of my boards after sanding them, which is apparently a sign of sanding too hard. Is there any way of judging how lightly one should press while "lightly sanding"?  Any way of checking other than just running a finger across the surface (possible health risk?)? Also, I understand that a 150 grit sandpaper is a bit too rough and something in the range of 200-250 would be better?
    Finally, is it worth buying an electric sander? I think it might give me a more uniform result, but I'm not sure if it won't be sanding too much even with the lightest touch given the speeds involved.
  • Question asked 2017-02-25 09:41:10 ... Most recent comment 2017-03-20 14:26:00
    Solvents and Thinners Varnishes
    Question
    I forgot to ask in my previous question: in addition to shellac not fully dissolving in a weak formulation, are there other consequences to using a denatured alcohol with a less than optimal percentage of ethanol?
  • Question asked 2017-03-18 22:34:27 ... Most recent comment 2017-03-19 03:41:00
    Sizes and Adhesives Flexible Supports
    Question

    ​Hi,

    I know it is better not to seal the back of your canvas. But what will happen if you stretch reversed primed linen onto you stretcher bars? Is that equally bad?

  • Question asked 2017-03-08 11:44:47 ... Most recent comment 2017-03-15 21:04:00
    Egg Tempera Grounds / Priming Rigid Supports
    Question

    ​i have read the descriptions for how to make real ET paint (fairly easy) and real ET panels with rabbit skin glue and whiting (very laborious).

    I cannot believe that lazy people like me who buy ET in tubes still have to make a panel. Panels with true gesso on are availale from few retailers and are expensive. Sennelier make passing reference to use on canvas with acrylic gesso, but their information is very poor.

    Are you able to offer advice on using these tubed ET paints with commercially available wood panels with acrylic gesso, please?


  • Question asked 2017-03-15 06:53:44 ... Most recent comment 2017-03-15 16:55:00
    Flexible Supports Grounds / Priming
    Question

    ​I've come across conflicting information on this.

    Some old manuals advise us to seal the canvases also from the back to protect them from humidity. Japan size and tin foil were highly recommended to do so.

    On the other hand, I've read that canvases sealed from behind perform worse than canvases where the linen fibers were left to breathe. 

    What is your opinion on this topic?

    Cheers. Nelson

  • Question asked 2017-02-14 13:09:24 ... Most recent comment 2017-03-08 17:26:00
    Acrylic Industrial and Non-Traditional Products Scientific Analysis
    Question
    I am interested in finding a list of Golden Paints  acrylic fluid color density, both fluid and high-Flow, as compared to one another and not to oil or a lacquer based paint. Can you help?
  • Question asked 2017-02-25 09:31:58 ... Most recent comment 2017-03-03 14:52:00
    Solvents and Thinners
    Question
    I make a point of searching out and buying a 190 proof (95% ethanol) denatured alcohol for making shellac.  However many of the denatured alcohols sold at hardware stores contain lesser percentages of ethanol (i.e. a student just asked me about "Sunnyside" brand; the MSDS reveals it is only 86% ethanol).  If someone prefers to buy whatever denatured alcohol is available at their local hardware store, at what percentage number does the ethanol in the formulation become too low to be suitable as a thinner for shellac?

    Also, the MSDS for Sunnyside's denatured alcohol lists "hazardous ingredients", which add up to about 94%.  What is the other 6% or so percent composed of?

    Thanks
  • Question asked 2017-02-27 22:04:58 ... Most recent comment 2017-03-02 11:11:00
    Animal Glue Chalk Grounds / Priming Oil Paint
    Question

    I’m student at an academy of fine arts in Europe. I used to paint on Wood and primed with acrylic gesso from Golden. I recently made the change to canvas and home made ground and that’s where the nightmare began. The priming recipe for oil painting on canvas given by my teacher consists of Rabbit Skin glue, Champagne Chalk (with optional titanium white) and Lindseed oil varnish. I made the first 5 with him and got excellent results but since I have had to make them by myself, I lost a month of painting and so much material because all my primed canvas cracked, I cannot understand why…

    1) I mix 55g of RSG with1L of water overnight in the fridge2)Take one part of that with 2.5 Part of water and do one layer of sizing3) Take on part with 2 part Champagne Chalk with 1 Part water with 1/3 Lindseed oil varnish and use an electric mixer. Then I apply 3-4 coats

    The next day I arrive and everything show mini cracks. I can hear them if I press gentle on the back of the canvas

    I have asked 50 times my teacher and I swear I’m doing what I think he tells me, but obviously something I do is wrong… Do you have any idea what the problem is? do you recommend another method specifically

    I use cotton duck canvas which I stretch. It is for oil painting. I like firm tension but that can take some rough cloth rubbing and handling. Longevity and quality are very important to me.

  • Question asked 2017-02-28 08:31:01 ... Most recent comment 2017-02-28 10:55:00
    Oil Paint Pigments
    Question

    ​I stopped using a newly opened large tube of Windsor and Newton titanium white that I had on hand because it contained "a small amount of zinc" according to the manufacturer. I suspect there is a growing amount of zinc containing paint being abandoned. Obviously, pure zinc white is disocuraegd but it would be great if there was some sort of guidance as to how much zinc is acceptable in a multi-pigment colour. In medicine there is an expression that goes something like "the dose makes the poison". Similarly, I expect that a very small amount of zinc isn't going to cause a problem but I haven't seen any research or guidance as to just what that maximum tolerance for zinc is. Is there any current guidance on this or research that you know of under way to clarify this issue? 

  • Question asked 2017-02-23 12:53:15 ... Most recent comment 2017-02-24 11:51:00
    Rigid Supports Sizes and Adhesives Grounds / Priming
    Question
    When applying a glue size to a fibreboard (MDF) panel, does the strength of the glue need to be stronger than the quantity of glue mix used in gesso?  I have been advised by my supplier to use a stronger formula for the inital sizing (1:10) but I haven't found this advice anywhere else.
  • Question asked 2017-02-21 17:04:22 ... Most recent comment 2017-02-21 17:48:00
    Drawing Materials Dyes Environment Ink Paint Making Pigments
    Question
    Hello! I'm a painting and drawing senior BFA student at the School of the Art Institute of Chicago and was wondering if you have any information or insight on residencies, workshops, or any opportunities that will allow me to engage in foraging and collecting my own materials, extracting organic pigments, making my own inks and paints, etc. Anywhere in the world! I hope to turn this into a fulbright scholarship application, so anywhere you suggest will help!

    I am interested in organic material, traditional processes, smaller communities and working in the natural environment... And of course, something very immersive. Even paper-making and natural dye techniques are helpful suggestions, but I'd love to just make materials from scratch. Thank you so much for your help!!
  • Question asked 2017-02-21 14:07:43 ... Most recent comment 2017-02-21 15:36:00
    Egg Tempera Rigid Supports
    Question
    To minimise warping when painting with ET on large panels 2ft x 3ft  (12mm MDF), I have previously gessoed both sides (8 layers or so) of my panels after a coat or two of rabbit skin size.  However this is a laborious technique owing to the drag of the gesso on such large panels.  Can I apply rabbit skin glue instead (8-10 layers) which glides on much more easily.  I am not inclined to brace/bracket my panels so any advice on alternative methods of stabilising large panels would be most welcome.
  • Question asked 2017-02-16 16:34:18 ... Most recent comment 2017-02-16 17:47:00
    Flexible Supports Acrylic
    Question
    Is Tyvek a sustainable surface for an acrylic painting?
  • Question asked 2017-02-16 16:36:53 ... Most recent comment 2017-02-16 17:47:00
    Drawing Materials Varnishes
    Question
    What's the best brand/material to fix a pencil on Canson drawing paper? I've used sprays before, just interested in what others are using. Thanks.  
  • Question asked 2017-02-14 22:43:54 ... Most recent comment 2017-02-15 10:41:00
    Oil Paint Paint Mediums
    Question
    I was wondering how much medium one could safely add to glaze layers.I remember the question being asked years ago on the old AMIEN forum, and there didn't seem to be a clear-cut consensus. One reply suggested that the ratio almost didn't matter, as long as the glaze was applied thinly enough. In the opinion of the moderators, how much leeway do we have regarding the amount of medium in very thin glazes? Let's say we have a glaze which is half paint, half medium, brushed on then patted down with a sponge - basically tonked - leaving more or less a residual stain of colour. In a glaze layer this thin, is the high amount of medium likely to cause any problems? I'm assuming if yellowing is a problem with oiling out, it might be something to worry about here too. And could we expect several ( similarly extra-thin ) layers of glaze, applied over each other, to develop the same problems that a single, thicker layer of medium-heavy glaze might, yellowing or even wrinkling? As always, any advice would be greatly appreciated.
  • Question asked 2017-02-15 08:19:14 ... Most recent comment 2017-02-15 10:40:00
    Egg Tempera Matting, Framing, and Glazing
    Question
    Egg Tempera artists are sometimes told to frame work under glass, to protect the initially vulnerable surface of tempera from scratches.  Both tempera's ground (traditional gesso) and support (wood-based panel) are hygroscopic.  Does framing egg tempera under glass protect the work from ambient moisture, or is glazing more likely to trap moisture, potentially leading to mold, delamination, etc.? 

    Thanks,

    Koo Schadler
  • Question asked 2017-02-14 14:53:57 ... Most recent comment 2017-02-14 15:01:00
    Art Conservation Topics Gilding Matting, Framing, and Glazing
    Question
    I gild the bevels of my archival mat boards, and I am wondering if this affects their archival-ness.  I use acrylic paint, water-based size, and 23K or other genuine gold leaf.
  • Question asked 2017-02-14 13:19:10 ... Most recent comment 2017-02-14 14:22:00
    Acrylic Industrial and Non-Traditional Products Scientific Analysis
    Question
    Regarding my question about a comparison of the Density of The fluid paints, I am mixed media and collage artist and use pours. I would like to have more control by knowing this simple fact.
  • Question asked 2017-02-13 16:26:34 ... Most recent comment 2017-02-13 17:53:00
    Grounds / Priming Rigid Supports Sizes and Adhesives
    Question
    I plan on painting on rigid, absorbent supports (HDF/MDF/hardboard etc.). Is it okay to speed up the drying time of PVA sizes and acrylic dispersion grounds using a hair dryer? Specifically, is it okay to:
    1) Speed up the drying time of the size before applying the next layer?
    2) Speed up the drying time of the ground before applying the next layer?
    3) Speed up the drying time of the ground before painting?
    In any case, how long should I wait before starting the next step/how do I know that the layer is dry enough? I have read the 24 hours drying time recommendation for acrylic ground before beginning a painting, but are there any estimates for the rest?
  • Question asked 2017-02-10 12:14:42 ... Most recent comment 2017-02-10 12:35:00
    Grounds / Priming Industrial and Non-Traditional Products Rigid Supports Sizes and Adhesives
    Question
    It appears there are conflicting recommendations on various manufacturers' websites regarding sizing HDF/MDF before applying acrylic ground. Looking at the table in the "Adhesives and Sizes" document, three coats of acrylic ground should be enough to protect from any noticeable migration of mediums or solvents through the support, so shouldn't it also be sufficient to protect the work from the chemicals that might migrate from the support?
    Assuming that sizing is still recommended, should PVA glue with a pH of 7 suffice? If so, should it be diluted? How much?
    Also, when using HDF/MDF that's laminated on one side, is it fine to leave the laminate as is, since it's already a protective layer?
  • Question asked 2017-02-09 18:00:49 ... Most recent comment 2017-02-09 18:45:00
    Paint Mediums
    Question
    I work in oils and would like to know the best choice for a medium when i am painting alla prima.  I only feel the need for a tiny amount of medium if I feel the paint directly out of the tube is too stiff, otherwise, I don't use it.  Should i use straight linseed oil, straight stand oil, a dilution with OMS of either of these, or somehing else?  I am not looking for something to make the paint dry faster.  Thanks in advance.  
  • Question asked 2017-02-09 07:07:14 ... Most recent comment 2017-02-09 10:39:00
    Grounds / Priming Industrial and Non-Traditional Products
    Question
    Given that I've heard from many people that exterior acrylic paints (hardware store ones) perform quite well as a ground for oil/acrylic paintings, and that "artist's gesso" is very expensive and hard to obtain where I live, I would like to ask for expert advice regarding their use.
    I have read the "Myths, FAQs, and Common Misconceptions" section on industrial/outdoor products, but the claims made there are very vague an nebulous. "can potentially lead to problematic consequences" and "Some of these additives are known to eventually migrate out of these commercial paints after a certain period of time" sound more like marketing claims made to instill fear and uncertainty, especially since they do not cite any works published in scientific, peer-reviewed literature. One could just as well make an argument that since none of the manufacturers of artist materials release their full formulations, those could just a well produce similar problems.
    Therefore, aside from this clarification, I would also like to ask about recommendations for ground alternatives for engineered wood (specifically HDF and MDF).
  • Question asked 2017-02-05 17:39:35 ... Most recent comment 2017-02-05 17:43:00
    Flexible Supports
    Question
    What is the very best way to tighten a stretched canvas ( no keys, rigid stretcher frame) ?  I have  just stretched a 40 x 48 canvas with  an excellent tight "thong" sound when finished ( one week ago). Now, it has relaxed - no sags, nor pulls- but just not as tight as I like to paint on. ( info: Fredrix's Dixie 123, acrylic pre-primed roll) THANK YOU for your kind reply in advance.
    Nancy
  • Question asked 2017-02-02 09:43:44 ... Most recent comment 2017-02-02 17:29:00
    Oil Paint Varnishes
    Question
    I understand that there may be a temporary yellowing of a fresh paint film, if it is stored in the dark, which is reversible with the application of sunlight, and there is a more long term, permanent yellowing that occurs over decades, if not centuries.____Isn't this long term yellowing due more to the aging of damar, copal, or other or other varnishes used in  or on  the top of the paint layer than to the drying oil used in the paint layer?_____Thanks for your thoughts.___Richard
  • Question asked 2017-02-02 13:41:33 ... Most recent comment 2017-02-02 15:55:00
    ASTM Drawing Materials
    Question
    I have noticed a lot of my favorite contemporary artists, like Colleen barry and Scott Waddell, make use of these prismacolor color pencils, for some pretty exceptional work. I question the durability of the material though. Prismacolor does not have a chart on this line of pencils. Specifically,
    Carmine red
    Scarlet red
    Vermilion
    Tuscan red
    Terra cotta
    Brown
    Black
    Tuscan red
    Terra cotta
    Brown
    Black
    I know the cpsa has their workbook, but I am a very poor artist and don't have 45$ currently.
  • Question asked 2017-01-31 09:37:19 ... Most recent comment 2017-01-31 16:08:00
    Alkyd
    Question
    Recognizing the increased flexibility and speed of drying in alkyd paint films over linseed oil/stand oil paint  films...

    1.   Would you recommend the use of alkyd mediums or alkyd paints over traditional oil mediums and paints for the most permanent, strong, flexible, non cracking and non-yellowing paint film?

    2.  What are the disadvantages of alkyd mediums, if any?

    3.  As alkyds in artist oil paints are only a few decades old, how confident are you that alkyd mediums will continue to out pace oil mediums in producing superior paint films?

    4.  To minimize the use of driers, would it be advisable to seek an alkyd synthesized from drying oils, linseed or walnut, vs non drying oils, safflower, soy, sunflower, etc?

    Thank you so much for your expertise.

    Richard
  • Question asked 2017-01-31 11:51:09 ... Most recent comment 2017-01-31 16:07:00
    Drying Oils Alkyd
    Question
    How does a walnut oil film compare with a linseed oil film in strength and flexibility?......   I know that it is a slower drying oil and will eventually reach the same level of yellowness and embrittlement over the course of decades as linseed, but will take longer to do so.......  I am considering the use of a walnut alkyd, added to a walnut oil medium to compensate for the slower drying time of the latter. .... .. The lower viscosity of both, vs stand oil with an added alkyd medium, would then require less OMS to thin it out, resulting in reduced solvent evaporation in an enclosed studio.   (I live in MN.   Either the heat is on or the air conditioning, ha, ha)....   Walnut oil is also drying oil and I suspect that a walnut alkyd may use less drier in manufacture than those alkyds made from semi-drying oils....Thank you for your thoughts....Richard
  • Question asked 2017-01-26 21:34:58 ... Most recent comment 2017-01-29 16:27:00
    Sizes and Adhesives Rigid Supports
    Question
    pva size for birch panel?
  • Question asked 2017-01-29 10:47:47 ... Most recent comment 2017-01-29 12:41:00
    Alkyd
    Question
    1.  Is the speed of drying in alkyd mediums and paints due to the chemical nature of of the alkyd compounds themselves, or are driers usually added to achieve their drying speed?

    2.   I understand that not all alkyds are created equal, being synthesized from different oils.   Do some alkyd mediums form stronger, more flexible paint films than others?  (In other words, are they all equally good in forming a reliable paint film?)



    I'm trying to avoid excess driers, as they tend to promote cross linking of the paint film indefinitely (faster embrittlement), but wish to speed up the drying time  of titanium white to be comparable to cremnitz white, which I may abandon use of because of cost.   Was thinking of using a small amount of alkyd medium in a stand oil medium to compensate for the slow drying time of titanium,  i.e. 10% alkyd, 30% stand oil, 60% OMS.

    Thank you for your insights,

    Richard

    PS   I dislike being held hostage to the much higher cost of cremnitz white and am seeking the next best alternative for painting landscape on panels.   I will miss cremnitz, however.
  • Question asked 2017-01-26 18:01:16 ... Most recent comment 2017-01-27 01:20:00
    Flexible Supports Other
    Question
    Hi, would you recommend coating a new wood stretcher with a coating of some kind, such as a water-borne polyurethane to seal the wood? Should I be concerned about volatile emissions from the bare wood on my cotton or linen canvas over the long term? The stretcher bars are bevelled. Thanks.
  • Question asked 2017-01-26 21:34:15 ... Most recent comment 2017-01-27 01:18:00
    Question
    birch support
  • Question asked 2017-01-26 10:01:22 ... Most recent comment 2017-01-26 10:11:00
    Oil Paint Pigments
    Question
    With concerns regarding the use of any quantity of zinc white and the increasing use of safflower and walnut oil as a binder in white oil paint, what alternatives, if any, do we have to purchase a good film forming white as an alternative to the increasing unaffordable lead or cremnitz white?

    Safflower, walnut and poppy oil are not thorough driers, zinc becomes brittle and apparently affects both titanium and lead white when used in any quantity, titanium creates a "spongy" paint layer that is not tough, but cremnitz white is increasingly unaffordable or contains one of the above oils above or zinc, in some cases.   Any recommendations?   Which poor alternative do I choose?

    PS  I paint on panels and use stand oil as a medium, with lead white, so that film toughness and flexibility are maximized on an inflexible support.

    Thank you for your insights.

    Richard


  • Question asked 2017-01-24 12:43:49 ... Most recent comment 2017-01-24 13:55:00
    Chalk Drawing Materials Pencil
    Question
    I am curious about what the white chalk of the old masters was made of, and where it might be found today. Currently I use generals white charcoal pencil, which I believe is some proprietary blend, and am curious about its lightfastness. I contacted generals but have yet to hear back.
  • Question asked 2017-01-21 10:10:27 ... Most recent comment 2017-01-21 10:35:00
    Art Conservation Topics Flexible Supports Mural Painting Oil Paint
    Question
    What is the better/best painting support for large scale easel painting (Las Meninas or The Raft of the Medusa come to mind)
    I personally find myself between a rock and a hard place when it comes to large scale painting supports. As many of these forums have explained, the hard panel surface is far more structurally sound than its canvas/linen counter part. On the other hand, when you want to create painting larger than sheet material size, the seam will undoubtedly rear its face during the life of the painting. I realize there are also ways to join boards to make a larger sheet surface, but my gut tells me those seams could cause problems down the line, as well. There may not be an ideal surface, but is there a best surface for this endeavor?
  • Question asked 2017-01-20 11:09:48 ... Most recent comment 2017-01-20 11:33:00
    Art Conservation Topics Pigments Scientific Analysis Technical Art History
    Question
    I have the good fortune to have acquired an 18th century British family portrait.  The painting has an inscription that dates it to 1754.  I am taking X-sections in hopes to study the layer structure, pigments and possibly help with an artist attribution.  The work is unsigned but similar to other works by Arthur Devis a British portrait painter who was active in London at the right time.  As I rarely work on paintings that are not American 19th century works I welcome any advice or insight.  I do have sampling opportunities in many different colors in the painting (according to areas of loss). 
    Thank you in advance
    Nina Roth-Wells
  • Question asked 2017-01-19 10:25:33 ... Most recent comment 2017-01-19 11:45:00
    Technical Art History
    Question
    Deseo saber sobre composición,materiales materiales en las obras de arte victoriano sobre todo en John w. Waterhouse.
  • Question asked 2017-01-17 08:43:08 ... Most recent comment 2017-01-17 08:53:00
    Egg Tempera Other Rigid Supports
    Question
    1. Does shellac discolor with age?  I’ve read both that it’s photostable (whatever degree of yellow is present when it’s initially made, depending on the cut, does not change over time) and also that it gets more yellow with age.   I have a 18 year-old test strip that shows no color change so far, but perhaps that’s not long enough to say.  Has there been testing on the yellowing of shellac?

    2.  My understanding is that shellac gets brittle with age.  If I’m using it as an isolating layer on tempera (which also gets brittle with age) on a panel, does the solidity of the support address this concern?  Or is brittleness always a concern, regardless?

    3.  I believe shellac becomes increasing resistant to solvents as it ages – is this irrelevant if its purpose is to isolate?  In the case of isolating, could this be a sort of benefit, like a paint film curing and becoming insoluble, so to speak?

    Thanks as always for your help.  Koo Schadler
  • Question asked 2017-01-09 16:55:26 ... Most recent comment 2017-01-09 17:13:00
    Drawing Materials Storage
    Question
    I have a growing stack of drawings on paper in graphite, charcoal, conte.   Is it really necessary to  interleaf the drawings? And is Tyvek the best material for these types of media? If you're on the site it says glassine is not good for long-term storage and mylar has electro static charge so I'm just wondering how I can store my drawings. Thanks.
  • Question asked 2017-01-07 17:03:07 ... Most recent comment 2017-01-07 17:24:00
    Oil Paint
    Question
    Is it safe to apply fresh paint over or into a layer of paint that has begun to set and has become tacky? Is it safe to blend tacky paint? Can either of these cause adhesion problems, etc.? No medium is being used, only a little bit of solvent.
  • Question asked 2017-01-07 13:13:02 ... Most recent comment 2017-01-07 13:16:00
    Question
    What is opinion of conservators and specialist about paint with oil colors on acrylic gesso. Will have problems and delamination for oil colors after years ? Thank you .
  • Question asked 2017-01-07 13:09:59 ... Most recent comment 2017-01-07 13:15:00
    Industrial and Non-Traditional Products Oil Paint Studio Tools and Tips
    Question
    Dear all, I am facing a problem. I am an art reproduction specialist, and until now I have been making all of my canvasses, from stretching on the frame, to prime grounding. I had done only one medallion in my career, and with success. It was longer than stretching a canvas on a square frame, but it wasn't that difficult. There were no folds, and I used tacks. I recently had a new order with a medallion format, and to save myself some time, I tried ordering to a national specialist a handcrafted but ready-made medallion canvas. I was shoked to receive it, first in only a thin cellophane wrap, but worst is, the cloth was stretched with staples, onto the back. Also the staples were put very close to one another, it felt like the number was too much, and they were not regularly applied. As a conservator too, and being aware of the quality of the materials I use, I find this outrageous.
    I called the craftman to complain but he assured me during an hour that nobody ever complained, that that's how it's done, never in is career anyone said otherwise, and should I have wanted tacks instead of staples I should have asked. Now, again, this company is specialized in traditional, handcrafted canvasses, and their clients range about all the national museums.
    I am lost here, what are your hints on the subject ? Am I to idealist to ask for tacks on a medallion canvas ? He said this would not have allowed to avoid folds entirely, but again, I did one myself with success. What do you think, do museums allow art reproductions to be made in these conditions ? Thank you again for your answers.

    S.G
  • Question asked 2017-01-06 17:14:48 ... Most recent comment 2017-01-06 17:20:00
    Acrylic Flexible Supports
    Question
    Hi, What kind of issue can I expect if applying acrylic paint on Color-aid paper? It will be adhered to cold press illustration board.  Thanks
  • Question asked 2017-01-06 13:31:16 ... Most recent comment 2017-01-06 13:32:00
    Matting, Framing, and Glazing Other
    Question
    Hello! I would like to know what is the best way to record what materials I used (pigments mediums and varnishes on the back of the canvas) I was thinking about going to a printshop and getting this info printed on canvas and gluing this small patch to the back of the artwork, but i am afraid this might disfigure the artwork down the line, same with using permanent markers. I will appreciate your input and help! Thanks!
  • Question asked 2017-01-06 12:24:16 ... Most recent comment 2017-01-06 12:30:00
    Flexible Supports Acrylic
    Question
    Hi, I have 84x30 inch canvas that is sized and primed, Gamblin PVA and Oil Primer. It is stretched on those 1x2 so called gallery stretchers. No matter how tight I try to stretch it I still get a wobbly bounce after each brush stroke. Is it safe to apply GAC 400 the back of the canvas to try and stiffen it up and reduce the movement, The stretcher can't be keyed. Thanks.
  • Question asked 2017-01-03 13:54:46 ... Most recent comment 2017-01-03 16:17:00
    Grounds / Priming
    Question
    Hello, I would be interested in knowing what you use for priming on canvasses, what are your recipes and ways of applying ? Precisions on century accuracy and references would be very much appreciated ! Thank you in advance for sharing your discoveries and works on this very basic but fondamental subject.
  • Question asked 2017-01-01 13:43:55 ... Most recent comment 2017-01-02 09:39:00
    Egg Tempera Pigments Paint Making
    Question
    How do you grind lead white? It seems to float on the surface of the water.
  • Question asked 2017-01-01 14:23:56 ... Most recent comment 2017-01-02 09:39:00
    Egg Tempera Gilding
    Question
    Can you place gold leaf over an area that has been painted in egg tempera?
  • Question asked 2016-12-28 19:10:49 ... Most recent comment 2016-12-28 19:17:00
    Egg Tempera Varnishes
    Question
    I have been experimenting with varnishing egg tempera paintings and have several questions I’d like MITRA’s input on.

    1.  As with oil, it’s generally presumed best to wait until a tempera painting has polymerized before varnishing (understanding that polymerization is dependent on number and thickness of layers, drying conditions, etc.)   Polymerization in ET seems to me to occur within 3 to 6 months; to test I either polish the surface (cured paint has a certain feeling of hardness) and/or carefully wipe a corner with a damp rag (the water beads up, no paint lifts).  These ideas come from my experience, not from any definitive timeline or test from a conservator.  Is there consensus on how long it takes, more or less, for an egg tempera painting to cure, and how to test for polymerization?  

    2.  Having spent a couple of decades experimenting with varnishing tempera, I’ve come to believe an isolating layer is necessary (at least on a relatively new tempera; it may be different for a centuries-old painting).  In my experience an egg tempera surface, whether a day or year-old, is still absorbent enough (because of high PVC) that varnishes sink in to varying degrees.  Since any layer applied directly atop seemingly becomes linked with the underlying paint, it seems best to first cover the tempera with a very thin layer of an isolator (I’ve experimented with casein, shellac, B72, Golden’s GAC500 & Gel Medium, Laropal, PVA both water and acetone based), then put a reversible varnish on top of the isolator.   This allows the varnish to go on evenly, stay distinct from the paint layers, and be reversible.  Your thoughts?

    3.  If the above is true – it works best to isolate a tempera before varnishing – does it matter how long the tempera has polymerized before applying the isolator (since the isolator becomes linked with the paint regardless of the paint’s age)? 

    Well, I have more questions, but that’s enough for now!

    Thanks,

    Koo Schadler
  • Question asked 2016-12-27 13:10:38 ... Most recent comment 2016-12-27 17:53:00
    Acrylic
    Question
    Hi,
    I'm a painter using acrylics and am thinking about incorporating wax medium (typically geared towards oil paint)  into the acrylic paint. Will the wax medium merge well with polymer based paint?
  • Question asked 2016-12-26 14:40:03 ... Most recent comment 2016-12-26 16:05:00
    Acrylic Flexible Supports Art Conservation Topics
    Question
    I have a very tiny (1/4") tear (slit) in an acrylic on canvas.  Is there a way to safely repair this?
  • Question asked 2016-12-24 12:25:56 ... Most recent comment 2016-12-24 17:21:00
    Egg Tempera Grounds / Priming Rigid Supports
    Question
    I have a few questions about SID (support induced discoloration) relative to traditional gesso and egg tempera.

    1.  The “Rigid Supports” article posted on this website, when discussing hardboard, says “SID will occur if the oily or resinous material migrates through the size or seal and and stains the ground or paint layers”.  My understanding is that oils and/or resins in or atop engineered wood-based panels are stable and cannot move or migrate – they are polymerized or cured and can’t go anywhere.  Yes, no?

    2.  My understanding is that SID is caused by materials in the wood itself (tannins, dirt, sap, starches), drawn up into the gesso by water based grounds and paints.  Yes, no?

    3.   Has there been testing to see if SID occurs in a traditional gesso ground and/or egg tempera?  I’ve done a couple of tests myself (painting a word on a panel using GAC 100, applying traditional gesso all over, seeing if the word later appeared) - very little to no SID appeared.   Could the very high solid content (percentage of chalk) in traditional gesso inhibit SID? 

    4.  The various products for blocking SID (Archiva-seal, GAC 100, PVA) are all polymer based and designed to sit under acrylic or oil grounds, not traditional gesso. I tried a crosshatch adhesion test of traditional gesso atop GAC 100 and adhesion was not great.  If SID is a concern with egg tempera, any ideas for how to block it?   I presume a layer of cloth applied with PVA to a engineered panel would do it, but is there a simpler option?

    Thanks!

    Koo Schadler
  • Question asked 2016-12-23 16:02:53 ... Most recent comment 2016-12-23 16:42:00
    Rigid Supports Oil Paint
    Question
    I just asked about painting oils on birch plywood, which I do directly, no primer. To see an example go to www.bowerart.com> galleries> painting and click on the thumbnail at the bottom left of a man in a blue sweater. That is an example. you can see the raw wood of the plywood. The painting is 2or 3 years old an looks like the day I painted it. Will it hold up for 500 years?
  • Question asked 2016-12-23 15:50:16 ... Most recent comment 2016-12-23 16:39:00
    Question
    Is it archival? I have painted on quarter inch birch plywood and like it a lot. i like the mid tone, surface, absorbency, durability, light weight, price and it has never shown a problem. I sometimes do not even seal it but paint right onto it, never a problem so far. Some opine that over time the oils will do this and that especially without priming, much like with canvas. Some say ue "marine" plywood only. Anybody?
  • Question asked 2016-12-21 21:28:35 ... Most recent comment 2016-12-22 13:11:00
    Drawing Materials Flexible Supports Industrial and Non-Traditional Products
    Question
    There are a lot of artist starting to use terraskin as a paper alternative particularly those doing metal point.  Their website explictly says that the stuff is designed to degrade under "the right environmental conditions" of heat, moisture and UV light.  For this reason it seems to me very risky to use.  Others argue that if kept indoors and protected from UV light it should be fine.  I don't think once an artist sells a piece of work that they have any control over how it is displayed.  Could you please weight in about the potential longevity and issues of these stone "papers" for fine art work?
  • Question asked 2016-12-21 13:06:33 ... Most recent comment 2016-12-21 14:31:00
    Oil Paint
    Question
    Are there good ways to prepare a layer of paint for overpainting that has become overly oily or slick?  Sanding with coarse sandpaper still leaves a surface that squeaks if I rub my finger across it.
  • Question asked 2016-12-18 02:22:48 ... Most recent comment 2016-12-18 11:22:00
    Oil Paint
    Question
    How can we best paint slowly to get a good structure in the painting? Meaning indirect painting such as subsequent corrections, revising the design, altering a colour,  glazing, scumbling (when you want the lower layer to be firm enough not to lift but you want to do it as soon as possible) or adding finishing details in fatter paint?

    Beyond starting with thin fast drying pigments or fast dry modified matte paints and observing critical pigment volume or fat. Beyond that, we mix different pigments with different drying times and change our minds. Which pigments are notorious for moving more as they dry? As a general guide for an average situation (knowing there are multiple variables including pigments and additions, weather and ground) how long is too short? eg skinned over paint that's still wet below shouldn't be painted over as it's still in it's active phase of weight gain and loss as it dries (is this typically 3-4 weeks for a thinnish, moderate drying time pigment in linseed oil with no driers or alkyds added?) How long should we wait before painting on top of a painting in progress? thank you
  • Question asked 2016-12-18 03:16:44 ... Most recent comment 2016-12-18 05:03:00
    Matting, Framing, and Glazing Rigid Supports Sizes and Adhesives
    Question
    Hello, I want to glaze (plexiglas) my paintings. What kind of rigid panel should I attach the canvas to that doesn't hold too much moisture beneath the finished painting? Hardboard is heavy and can warp. ACM can be expensive or tricky to glue canvas to. Does glueing the linen to the support using acrylic medium attract extra moisture?  Will framing behind glazing restrict the oxidisation of the paint? How much space is needed between the glazing and the painting and a rear board?
  • Question asked 2016-12-16 15:56:21 ... Most recent comment 2016-12-16 16:13:00
    Art Conservation Topics Egg Tempera Mural Painting Solvents and Thinners
    Question
    I'm trying to develop some glazing techniques to use on egg tempera paintings. I need to slow the drying time down. How should I go about this ?
  • Question asked 2016-12-14 23:46:43 ... Most recent comment 2016-12-15 00:03:00
    Question
    I mostly use GAC 700 and Specialty Polymers BH61 because I like their clarity when dry.  They both have very high solids content.  While they seem similar in many regards they are very different in their tackiness when dry.  GAC 700 is very tacky and BH61 is very hard.  I notice GAC 700 will be flexible soon after it is dry but BH61 will take weeks to become flexible.  After they are fully cured both can be bent completely over without breaking.  I wonder if the "gumminess" of GAC 700 occurs because it is made to be flexible sooner and if this occurs by an additive that creates the stickiness of the final film and what that additive might be?   I have tried propylene glycol but I don't think that is it.   Also I notice that BH61 will sometimes form fine cracks (not fissures) in certain drying conditions and I wonder if this is related to the tackiness?
  • Question asked 2016-12-14 18:30:40 ... Most recent comment 2016-12-14 18:34:00
    Rigid Supports
    Question
    I don't know if this is proper on this site to ask for the names of companies that offer already sized and primed canvas or linen mounted onto rigid supports that are archival and do not contain zinc white? I don't like to spend my time preparing supports. I know they will be more expensive when already prepped but it does save a lot of time even though I may still add another coat of oil ground or acrylic ground on top.  Thank you.
  • Question asked 2016-12-14 11:19:45 ... Most recent comment 2016-12-14 18:16:00
    Oil Paint Pigments
    Question
    Some paints are fast drying but have a high oil content to pigment ratio out of the tube.  Is it safe to use these in an underpainting?
  • Question asked 2016-12-13 19:44:14 ... Most recent comment 2016-12-13 21:14:00
    Flexible Supports Grounds / Priming
    Question
    I'd like to try painting on polyester canvas. Unfortunately, it's difficult to find artist polyester canvas where I live; equally difficult is getting untreated, "loomstate" polyester fabric. Easy to find, though, is polyester canvas for inkjet printing, and plain polyester canvas from the fabric store. My question is, are either of those an acceptable substitute, and safe to prime with acrylic gesso? I'm concerned that washing the canvas wouldn't properly remove the coatings it would have, causing adhesion problems for the gesso. Perhaps it would be be wiser to stick with cotton and polycotton canvases, made for artists, until a source for artist polyester canvas becomes available? Thank you.
  • Question asked 2016-12-12 06:24:22 ... Most recent comment 2016-12-12 11:55:00
    Handling and Transportation Oil Paint
    Question
    What is the best way to clean a dusty oil painting? Can I use a tack cloth? Should I pour water and wipe it off?
  • Question asked 2016-12-11 23:49:07 ... Most recent comment 2016-12-12 03:08:00
    Alkyd Drying Oils
    Question
    Do different paints with different oil binders, bond as strongly together as paints with the same oil binder? And does this apply to alkyd/oil bonds, considering alkyds are often derived from oils other than what is used as a binder in oil paint?
  • Question asked 2016-12-11 23:16:22 ... Most recent comment 2016-12-12 03:07:00
    Oil Paint
    Question
    How important is using pigments of low oil content in the underpainting for adhesion of later layers? I've had problems with adhesion, even when there was sufficient tooth in the underpainting, the overpainting can be peeled or scratched off easily to reveal the first layer.  I realized after that the Titanium White I used in the underpainting was especially oily, and the overpainting white I used was not.
  • Question asked 2016-12-11 22:56:34 ... Most recent comment 2016-12-12 03:06:00
    Oil Paint
    Question
    Is oiling out necessary for good adhesion between paint layers? If the layer is sunken in or matte, does it need to be oiled out? 
  • Question asked 2016-12-11 23:05:28 ... Most recent comment 2016-12-12 03:06:00
    Alkyd Oil Paint
    Question
    Is it safe to overpaint an alkyd/linseed paint with linseed paint?  These Gamblin Faste-Matte paints have a calcium carbonate additive to help with adhesion, but I am worried about varying degrees of flexibility between paint layers, especially because I use a lot of linseed Titanium White in the overpainting.  If not, is there a white you would recommend for underpainting?
  • Question asked 2016-12-10 19:33:02 ... Most recent comment 2016-12-10 19:42:00
    Grounds / Priming
    Question
    I have been instructed to use Shellac on Marine Plywood for a panel to paint on. The Shellac is obviously to seal the wood, but how do I get the ground to be white? Do I gesso the wood first?. Do I apply Gesso on the Shellac? do I mixe the Gesso WITH the Shellac? Once it is Gessoed, do I also need to put some kind of an Oil Paint Ground on it? I don't really like to do the prep work, I prefer someone else do the material preparation and I can just paint. I can't seem to get what I need pre-prepared however so my next wish would have been an all-in-one spray to make short-shrift of the work, but that doesn't appear to be available either.   POST SCRIPT: I actually asked this elsewhere and the artist who made the suggestion to me answered, knowing the effect I was after and said that I don't need any white or gesso at all to get the affect that I want.  The Shellac is intended as a sealer on the wood that is not too slippery or absorbent to paint on and to  allow the wet , streaky brush marks I am looking for, with the apricot wood color coming through.    However, what if I DO want the ground to be white?  Do I tint the shellac itself with lead white oil paint, Gamblin oil Ground, or Titanium White Oil?
  • Question asked 2016-12-09 09:16:08 ... Most recent comment 2016-12-09 10:34:00
    Oil Paint Paint Mediums Varnishes
    Question
    When using Oleogel as a medium, does the wax in Oleogel pose an issue to safely cleaning the painting in the future? Or create issues with the longevity of the painting by making it more susceptible to heat or other issues?
  • Question asked 2016-12-07 20:08:20 ... Most recent comment 2016-12-08 01:39:00
    Flexible Supports Storage Industrial and Non-Traditional Products Other
    Question
    Along the question about 'Terraskin', I want to know more about 'Tyvek'-- I have seen it used in a few installations recently, in sculptural applications. Other than the convenience and weight factor (compared to an actual heavy sculpture), what are your thoughts about its use? Best practice?

    And can this be adhered to canvas for dimensional effects? If yes, what did you use to adhere and how would you protect it for the future?
  • Question asked 2016-12-02 15:48:08 ... Most recent comment 2016-12-07 11:03:00
    Flexible Supports
    Question
    I have several used linen canvases which, rather than throwing away, I would like to reuse. Is this possible? Thanks in advance
  • Question asked 2016-12-04 14:37:35 ... Most recent comment 2016-12-07 11:03:00
    Oil Paint
    Question
    I am painting with Old Holland oil paints using a small amount of linseed as a medium, on linen canvas. My painting sometimes take several weeks to reach the first stage in completion. After that period I sometimes need to make small changes. At what point after the initial painting has been completed is it too risky to continue adding more changes? For example if I  'finished' a painting, could I then return to it six months after to make a change either a glaze or further painting?
  • Question asked 2016-12-04 15:32:55 ... Most recent comment 2016-12-07 11:03:00
    Grounds / Priming Oil Paint Rigid Supports
    Question
    I have some hairline cracks in my true gesso ground, im wondering if these will continue to get bigger and perhaps crack subsequent layers of oil paint. 
  • Question asked 2016-12-05 12:30:39 ... Most recent comment 2016-12-07 11:03:00
    Other Studio Tools and Tips Art Conservation Topics
    Question
    What´s the best way for a signature at the back of the canvas that wouldn´t eventually penetrate through the ground and paint layers and thus affect the face of the painting - become visible? (Size of the signature; how to dillute paint - oil (if at all) or acrylics that the color would flow freely in order to paint a signature on the unprimed/raw side of the canvas? Use of other dry mediums like chalk, graphit, pastel?) Thank you!
  • Question asked 2016-12-05 15:49:00 ... Most recent comment 2016-12-07 11:03:00
    Pastel Health and Safety
    Question
    Are there any health hazards when blending pastels with bare hands?
  • Question asked 2016-12-06 09:52:42 ... Most recent comment 2016-12-07 11:03:00
    Pigments Paint Making Paint Additives Paint Mediums Other
    Question
    Every now and then, I have to make conductive paint with my students. Up until now, I do it with graphite and acrylic binder, which sort of works. Sort of, because the acrylic is an insulator. So basically what I am doing now, is to underbind the paint, so it still conducts current.
    I know there are conductive binders though. Ulysses Jackson from Golden suggested polytiophene as a conductive binder, but I cannot find it anywhere. Does anyone know if there is another conductive binder that could work?
  • Question asked 2016-12-07 10:11:57 ... Most recent comment 2016-12-07 10:57:00
    Animal Glue Art Conservation Topics Drying Oils Flexible Supports Gilding Grounds / Priming Oil Paint Paint Making Pigments Rigid Supports Sizes and Adhesives Technical Art History
    Question
    I am searching for information on the use of red bole in oil painting. My understanding is that it is a clay [primarily used in building at this point] that can be diluted to cream consistency, mixed equally with warmed RSG, and applied over traditional gesso for toning a surface. Setting aside the structural debates of stretched linen/canvas surfaces, how can one use this over such a surface. Are there any pigments that approximate this clay, or is there an oil ground approach that provides a comparable alternative? Thank you for any time or considerations.
  • Question asked 2016-12-05 18:01:07 ... Most recent comment 2016-12-05 18:42:00
    Casein Flexible Supports
    Question
    In the resources here, in the Grounds and Primers PDF, it states that casein should only be used on rigid supports because it is brittle.
    However, at the site http://www.richesonart.com/products/paints/richesoncasein/richcaseinfaq.html, it states
    "Can Casein be used on stretched canvas?
    Yes, but you must remember to paint very thin because Casein can crack if it's applied too thickly. If you would like to paint thickly and would still like to paint on canvas, mount the canvas or linen on masonite, and prime the canvas with PVA, glue or acrylic gesso. Then go to town and paint as thick or thin as you please! "
    So my question is, is it true that casein can be used on stretched canvas if it is painted thinly?
    I can't see why a thin layer of casein would be any less brittle than a thick layer.
  • Question asked 2016-11-30 23:18:54 ... Most recent comment 2016-11-30 23:36:00
    Drying Oils Oil Paint Pencil Pigments
    Question
    I see warnings of the possibility of graphite migrating to the surface of an oil painting over and over again.

    I have been using graphite for over 40 years without seeing any migration, and considering that graphite is used as a pigment in oil, I'm inclined to think that graphite migration is a myth.
    Is there any evidence that graphite can or does migrate through oil paint?
    Note, I'm not talking about a drawing becoming visible because the paint over it has become more transparent over time.

    Thanks.
  • Question asked 2016-11-30 16:15:33 ... Most recent comment 2016-11-30 16:47:00
    Pigments Technical Art History
    Question
    What colors did Titian use
  • Question asked 2016-11-30 05:51:35 ... Most recent comment 2016-11-30 09:12:00
    Industrial and Non-Traditional Products
    Question
    I recently watched a video, on New York Academy of Art Facebook Page. Vicent Desiderio is using flashing cement in his work. I guess the reasoning being it is made to withstand harsh weather conditions, heat and cold. This must have some pit falls, even though he produces remarkably evocative beautiful work. Can this be considered a safe material to work with? Thanks, Steven Lewis
  • Question asked 2016-11-29 15:44:53 ... Most recent comment 2016-11-29 15:58:00
    Industrial and Non-Traditional Products Other
    Question
    I am looking for a hard black wax as a surface covering on cement sculpture. Hard enough to reject fingerprints. Any suggestions would be greatly appreciated.
  • Question asked 2016-11-29 14:10:40 ... Most recent comment 2016-11-29 14:17:00
    Chalk Oil Paint Other Paint Additives Paint Mediums
    Question
    What are your thoughts regarding mixing Chalk, calcite, barite, kaolin (clay), talc, silica (quartz) and bentonite directly into the paint or into the medium while painting. I love some of the effects that are possible when you add chalk or barite into your paint on the palette, but I'm worried about permanence. I don't use any mediums except for linseed oil and or stand oil.
  • Question asked 2016-11-29 07:35:26 ... Most recent comment 2016-11-29 09:25:00
    Mural Painting Rigid Supports
    Question
    It seems that traditional marouflage adhesives were made of mixtures of animal glue and starch paste. Such adhesives are generally strong and can last for decades, but are quite reversible by mechanical means. Are there any modern products that could be equally strong and reversible for adhering painted canvas to walls or ceilings? Perhaps commercial wallpaper pastes with the addition of animal glue? Are there any tried and true adhesive recipes for this? It seems they are hard to find.
  • Question asked 2016-11-28 18:39:45 ... Most recent comment 2016-11-28 20:23:00
    Acrylic
    Question
    I have recently been creating some abstracts using acrylics. In order to create cells I have watered down the paint considerably, ( it seems to be about density) Now that I have weakened the bond I was wondering if I use the pouring medium from Liquitex on top of the finished canvas or board, would that seal the painting underneath or should I use varnish or resin? Thank you!
  • Question asked 2016-11-28 16:18:20 ... Most recent comment 2016-11-28 16:23:00
    Drying Oils Environment Oil Paint Paint Mediums Solvents and Thinners
    Question
    Has any one of you experience with Lavender spike oil or Zest-it products to replace gamsol in the beginning of the painting process? I would like to work with more environment and health friendly products. Normally I use gamsol for the transparant wash and mix gamsol and lineseed for Amber underpainting. Lineseedoil in my first layer of full paint and stand oil in second layer. Than when finished a varnish. So if I start with a spike oil (which maybe does not give a stable paint layer) from the beginning in the first 2 steps, I need varnish in my second paint layer which Is not preferable. So how do I get a wash and underpainting transparant but still working or adapting all the fat over lean steps?
  • Question asked 2016-11-25 19:04:02 ... Most recent comment 2016-11-25 22:13:00
    Question
    Is Gamblin Rich Gold oil paint okay to use in outer layers in my paintings? I paint indirectly and will use it for small areas such as on a bird’s feathers or parts of leaves, etc. I don’t know anything about these metal paints and hoping they’re durable paints. I bought it on a whim. In case this is relevant, I only use a little linseed oil as my medium. Thank you for starting this site for artists!
  • Question asked 2016-11-23 01:39:58 ... Most recent comment 2016-11-23 09:09:00
    Question
    I have an encaustic work on a stretched headed canvas  that is delaminating. It is melted crayon. Can it be warmed to readhere it?.
  • Question asked 2016-11-23 09:03:55 ... Most recent comment 2016-11-23 09:04:00
    Art Conservation Topics Encaustic
    Question
  • Question asked 2016-11-22 06:01:00 ... Most recent comment 2016-11-22 07:14:00
    Rigid Supports Sizes and Adhesives
    Question
    What is the difference between BEVA 371, Beva gel and BEVA 371 film? The film is really quite expensive so I would rather buy a gallon and just paint it on, as long as that will have the same effect of reducing bubbles.
  • Question asked 2016-11-21 13:34:07 ... Most recent comment 2016-11-21 13:35:00
    Pastel
    Question
    20 year old pastel sticks Question: I have a fantastic collection of fine pastel sticks. From Schminke to Rembrant, to Windsor Newton, etc. Perhaps 1000. I had to stop using pastel due to living in very hot climates year round and limited interior work space/health. I am now ready to take pastel painting up again, and find that many sticks are pretty chalky and or dry. Is there any safe way to revive them? Thank you very much.
  • Question asked 2016-11-21 13:25:52 ... Most recent comment 2016-11-21 13:34:00
    Pastel
    Question
    I have a fantastic collection of fine pastel sticks.  From Schminke to Rembrant, to Windsor Newton, etc.  Perhaps 1000.  I had to stop using pastel due to living in very hot climates year round and limited interior work space/health.  I am not ready to take pastel painting up again, and find that many sticks are pretty chalky and or dry.  Is there any safe way to revive them?  Thank you very much.
  • Question asked 2016-11-21 13:27:08 ... Most recent comment 2016-11-21 13:34:00
    Pastel
    Question
    Title: 20 year old pastel sticks

    Question: I have a fantastic collection of fine pastel sticks. From Schminke to Rembrant, to Windsor Newton, etc. Perhaps 1000. I had to stop using pastel due to living in very hot climates year round and limited interior work space/health. I am not ready to take pastel painting up again, and find that many sticks are pretty chalky and or dry. Is there any safe way to revive them? Thank you very much.
  • Question asked 2016-11-21 09:32:51 ... Most recent comment 2016-11-21 09:42:00
    Grounds / Priming Drying Oils
    Question
    I was at. A product information session during which the paint company representative recommended applying linseed oil to the ground, wiping off all the excess until the surface appeared dry, allowing the surface to dry 24 hours as a solution/to avoid sinking in. Is this good practice?
  • Question asked 2016-11-20 17:09:09 ... Most recent comment 2016-11-20 17:39:00
    Studio Tools and Tips
    Question
    I'm now painting in a basement studio and the light is terrible. I bought white 5500Kelvin bulbs but to my dismay they look bluish... which are your favourite brands of white light bulbs? It can be any type of light bulb, as I can fit both halogen and fluorescent. Thanks.
  • Question asked 2016-11-19 23:55:34 ... Most recent comment 2016-11-20 00:02:00
    Art Conservation Topics Other Rigid Supports
    Question
    When adhering a painting on linen to an ACM/Dibond panel using BEVA (Solution or film) using a domestic iron, is it possible to sufficiently/successfully activate the BEVA by applying the heat to the back of the aluminium panel rather than the front of the linen/painting - in other words with the linen/painting side face-down rather than up? I ask because I've only ever applied the heat to the side of the Panel with the linen, but the reverse is always warm afterwards.
  • Question asked 2016-11-18 20:24:23 ... Most recent comment 2016-11-18 21:55:00
    Varnishes
    Question
    Hi everyone, which is the glossiest varnish or finishing technique that you know of? I'd like my paintings to keep that 'wet look' but damar is still not glossy enough... ideally a varnish that won't discolour over the years. I don't mind even burnishing it if you feel that can improve gloss? Thanks.
  • Question asked 2016-11-18 10:26:24 ... Most recent comment 2016-11-18 10:36:00
    Pigments
    Question
    What are your thoughts on PW12.77990?  I saw this on Kremer's online shop.
  • Question asked 2016-11-11 12:41:52 ... Most recent comment 2016-11-17 10:28:00
    Question
    Please do not approve this question, I am using it to test a new feature.
  • Question asked 2016-08-21 10:53:21 ... Most recent comment 2016-11-16 18:37:00
    Rigid Supports
    Question
    I am interested in learning more about appropriate ways to prepare an ACM panel
  • Question asked 2016-11-16 10:59:03 ... Most recent comment 2016-11-16 12:03:00
    Acrylic Oil Paint
    Question
    I recently over painted a work that I decided needed it.  The acrylic work had an area with R & F oil stick on it.  I thought the gel medium would allow this to be fine but need to ask.The R & F was rough.
  • Question asked 2016-11-16 00:07:22 ... Most recent comment 2016-11-16 06:18:00
    Acrylic Alkyd Flexible Supports Handling and Transportation Oil Paint Paint Mediums Storage
    Question
    I have been asked to paint a backdrop for a photographer, on a large canvas (5' x 8') with the following criteria:
    - the canvas will be rolled up so it must be flexible and not crack over time.
    - the end result must be matte, not shiny.

    I'm used to painting in oil, with a strong preference for oil, but I'm thinking acrylics would be the better choice. I"m thinking acrylic paint on canvas as acrylic can be flexible and inexpensive over a large area of canvas. There would be just two colours and those pigments are very inexpensive, but can be extended with a matte medium.

    Alkyd is also flexible, am I correct; and mediums could be added to oil paint, with a little bit of wax medium to matte it out, but I'm concerned with the flexibility of the surface if I use wax medium in any capacity.

    We don't expect this to last forever, but the photographer should be able to get the most of this for a long time. So I think we'd be happy if this piece can last for at least 5 years.

    What would be recommended?
  • Question asked 2016-11-15 11:11:44 ... Most recent comment 2016-11-15 13:39:00
    Art Conservation Topics Mural Painting Oil Paint Scientific Analysis Solvents and Thinners Technical Art History Varnishes
    Question
    I was encouraged to reformulate my FB question below here by Kristin DeGhetaldi. Feel free to moderate my message to be more on point and specific. Anyway, I wondered about the practice within the restorers/conservators community worldwide  on the removal of varnish or cleaning of historical paintings? Is there a consensus to tread really carefully when handling such a task? A standard procedure in place for assessing risks of overcleaning? One would assume that to be the case but the horror stories of overcleaned/altered works of art in the (sometimes relatively recent) past are plentiful, no? Is there consensus and acceptance across the field that irreversible errors were made in the past and a determination to avoid those in the future?
  • Question asked 2016-11-13 13:35:24 ... Most recent comment 2016-11-13 15:39:00
    Acrylic Varnishes
    Question
    Would Golden GAC 400 be OK to use as a final varnish on acrylic paintings? It foams less than Golden Polymer Varnish on a fairly rough surfaced acrylic painting. I see on the Golden site they recommend GAC 100 as an isolation coat before final varnish on acrylic paintings.
  • Question asked 2016-11-13 09:01:02 ... Most recent comment 2016-11-13 09:38:00
    Art Conservation Topics Sizes and Adhesives Solvents and Thinners
    Question
    Is the solvent Napthol, 'cut' 50:50 with BEVA 371b solution to adhere linen to Aluminum Composite Material, harmful to the un-sized & un-primed side of the linen (on the reverse side of the properly-prepared canvas being attached to the ACM) onto which it is applied?
  • Question asked 2016-11-13 09:05:48 ... Most recent comment 2016-11-13 09:11:00
    Rigid Supports
    Question
    What materials & procedure constitute 'best-practice' when cradling large pieces of Aluminum Composite Material (Dibond etc)  to prevent warping? What materials should be used for the cradle itself, and for adhering the cradle to the ACM panel?
  • Question asked 2016-11-11 09:59:36 ... Most recent comment 2016-11-12 22:20:00
    Art Conservation Topics Varnishes Rigid Supports
    Question
    Please give your suggestion on how to safely remove damar varnish, light touch up,  transfer canvas to aluminum support. Oil painting, 50 x 40", 30 years old
  • Question asked 2016-11-12 21:58:07 ... Most recent comment 2016-11-12 22:06:00
    Health and Safety Pigments
    Question
    I have heard that Italy and some other EU countries are considering outlawing pure cadmium colors as too many artists are washing their brushes filled with the paint into the water system.  For this reason I have learned to clean my brushes using no water.  Have you heard this and if so would you comment.  If not would you recommend a safe way to clean brushes that is good for the environment?  Thank you.
  • Question asked 2016-11-12 18:43:55 ... Most recent comment 2016-11-12 18:48:00
    Flexible Supports Rigid Supports
    Question
    Hello. I am aware of the consensus that (oil) painting on a rigid rather than flexible support is best-practice, but I still feel confused & unsure what to choose to paint on when I want to make large paintings; say 50" x 60" or larger - Aluminum composite is both hard to come-by where I live, and at 3mm thickness, is liable to bend at the sizes I'm talking about, unless cradled... but then I have been told that cradling often creates its own problems. These same issues go for wood panels too, with the added problem of increased weight & natural warp. So, back to the question: What should painters be working-on when they want to paint on a larger scale? Thank you.
  • Question asked 2016-11-12 17:11:58 ... Most recent comment 2016-11-12 17:16:00
    Drying Oils Oil Paint Pigments
    Question
    Is zinc sulfide embrittlement comparable to that of zinc oxide? As a pigment does it pose the same risks in a paint film?
  • Question asked 2016-11-11 14:35:12 ... Most recent comment 2016-11-12 12:23:00
    Drying Oils Varnishes Oil Paint
    Question
    I would like to make some changes to an oil painting which I thought I had finished. It is touch dry. I used Old Holland oils with a small amount of linseed oil as a medium. Should I use retouch varnish on the area I wish to rework? I have been told that I can put a layer of linseed on as an alternative to retouch varnish.. Advice much needed thank you Fiona McClean
  • Question asked 2016-11-12 05:28:41 ... Most recent comment 2016-11-12 11:49:00
    Pastel Matting, Framing, and Glazing
    Question
    I would be grateful to see any information your group might have or know of, historical or current, concerning the long standing practice by some artists of framing pastel works in direct contact with the glass -  specifically concerning mold / fungus growth. 
    <p>
    Of greatest interested would be any documented instances of mold / fungus growth that were known or  suspected to have been directly caused by this practice. Also wondering if there have ever been any studies or laboratory testing done to determine the propensity for mold / fungus growth of  pastel works in general and particularly those done on any of the current day sanded papers.
    <p>
    Please note that I am not looking for information concerning the alteration or disturbance of the pastel work by the direct contact with the glass as I have been able to test this extensively myself.
  • Question asked 2016-11-10 19:00:28 ... Most recent comment 2016-11-10 21:39:00
    Encaustic Varnishes
    Question
    What archivally sound permanent or removable protective finishes if any have been used/recommended for encaustic works that provide a more durable finish on top of the wax surface to help protect it from pollutants and contact damage? Under the recommendation of Golden products I have been using their removable acrylic varnish for about a year now with excellent results but would like to look at other options.
  • Question asked 2016-11-10 18:05:59 ... Most recent comment 2016-11-10 19:10:00
    Art Conservation Topics
    Question
    I inherited an oil portrait which is starting to show some damage, cracking especially in the very dark areas of the hair where the paint is thick. There are some tiny missing chips of paint as well. What can I do to prevent further damage and protect this paint as much as possible? Thank you, Mona
  • Question asked 2016-11-10 09:43:46 ... Most recent comment 2016-11-10 11:59:00
    Art Conservation Topics Flexible Supports Sizes and Adhesives
    Question
    ristin DeGhetaldi, I am researching sizing of canvas for stretched supports. I have tried both Gamblin PVA and GAC100 for preventing the leaching of oil to the canvas, to prevent rotting. I prefer using the Gamblin PVA, because it seems to soak into the canvas better, and therefore is easier to use (also, it is less cost prohibitive). However, I am still concerned about too much flexibility with either of these PVA sizings when used with acrylic gesso and stretched canvas. The fully cured oil paint will be more rigid than its substrate, which could lead to cracking, long term. To do it better, and get more compatible flexibility, I am thinking that adding GAC 400 might be a good option. This would make the substrate stiffer and of similar rigidity to the fully cured oil paint. Am I right here?

    If so, what would be the best order of operation? I am guessing a layer of Gamblin PVA on the front then back, before stretching, then a layer of GAC 400 on the front, after stretching. Then I would wait a day before gessoing twice with high quality acrylic Gesso, like Golden. Then, I would wait 3 or 4 days before painting. I would appreciate your opinion. Thanks!
  • Question asked 2016-11-07 22:12:01 ... Most recent comment 2016-11-08 07:48:00
    Technical Art History Art Conservation Topics
    Question
    I am wondering about the reliability of the information in Ralph Mayer's book the Painters Handbook? If not reliable and even if it is I would appreciate any and all recommendations.
  • Question asked 2016-11-06 17:27:55 ... Most recent comment 2016-11-07 01:28:00
    Egg Tempera Health and Safety Pigments
    Question
    I've recently acquired some dioptase pigment which was recommended by a friend. It seems to be very transparent and is a beautiful colour, so very useful as a glaze. I'd love to know any information on colour lightfastness and stability. I'm using it in egg tempera. I believe it's pretty toxic. Thanks.
  • Question asked 2016-11-06 22:06:23 ... Most recent comment 2016-11-07 01:28:00
    Pigments Technical Art History
    Question
    In another forum, this pigment was mentioned as a suitable pigment to use instead of verdigris.  Can you please tell me more about this pigment, the historical period it was used in and its stability and light fastness in egg tempera or oil painting binders?
  • Question asked 2016-11-06 04:20:42 ... Most recent comment 2016-11-06 05:27:00
    Question
    How do I see all posts on a subject.  Just want to read, no specific question yet.
  • Question asked 2016-11-05 13:08:33 ... Most recent comment 2016-11-05 21:24:00
    Egg Tempera Paint Mediums
    Question
    I'd be very grateful for some advice about egg tempera combined with oil glazes.
    I've read Koo Schadler's article on her website but I'm still wondering:
    1. Is it absolutely necessary to isolate the egg tempera with shellac?
    2. How long would you need to leave the ET to dry?
    3. What would be the best medium to use in the oil glazes? I bought some Rublev oil paint but I can't find any oleogel here in the uk.
    (I'm an experienced egg tempera painter).
  • Question asked 2016-11-04 11:15:37 ... Most recent comment 2016-11-04 11:24:00
    Storage Studio Tools and Tips Varnishes
    Question
    Oftentimes when my paintings are drying, they collect dust, hairs and schmutz that I need to remove before varnishing. If the paint layer is cured sufficiently, I use a foam brush and lightly brush over the painting to remove it. I wonder if a tack cloth can be used, or will that leave residue on the paint surface?

    What is the recommended way of removing inevitable dust from an oil painting?
  • Question asked 2016-11-03 10:33:55 ... Most recent comment 2016-11-03 13:03:00
    Egg Tempera Pigments
    Question
    I have recently found a good source of more or less affordable azurite.  The pigment is beautiful, easy to work with in egg tempera.  Its shade is also easily controllable by grinding more (it gets paler as you grind it).  However, one issue that I found bothers me a bit.  When I finish the work, it is a beautiful tone of blue with a hint of green in it.  However, after a few months, it gradually turns more and more green.  Not entirely objectionable, and in fact the color harmonizes better overtime.  But is there a way to stop it from greening?  I read somewhere that many egg tempera works and frescoes were done in azurite but it didn't green.
  • Question asked 2016-11-03 11:02:36 ... Most recent comment 2016-11-03 13:03:00
    Dyes Gilding Varnishes
    Question
    In some Russian icons of the 18-19 cc, there was a method of "gilding" without gold leaf.  Metal leaf (often silver leaf) was used, but then coated with a yellow-tinted varnish.   It didn't look like gold but had its own distinct charm and softness.
    Recently, I tried to replicate this technique by using aluminum leaf; however, I cannot find a suitable colorant for the varnish.  Kremer Pigments suggested something (organic pigments) but these turned out to be not soluble in a solvent-based varnish.  Even though the pigments were transparent, the varnish turned cloudy, just like you'd add a mineral pigment such as yellow ocher into any liquid. 
    Is there a type of dye that one can be completely dissolved in mineral spirits (i.e., solvent-based polyurethane varnish)?
  • Question asked 2016-11-03 07:46:23 ... Most recent comment 2016-11-03 07:56:00
    Ink Other Varnishes
    Question
    I have been asked to create an art work that will be between layers of shellac, on a guitar.  The client says the last time this was done, the artist used sharpies.  I'm concerned about how that will look years from now.  It needs to be very flat, so pigment pens might be the only way.
  • Question asked 2016-11-02 14:05:28 ... Most recent comment 2016-11-02 15:26:00
    Art Conservation Topics Environment
    Question
    Asking for a friend: She had some colored lithographs stored in a flat file that had some water damage. After laying out to dry, there's been some small mold growth on the edges/border. Is there a way that I can treat the area to prevent/minimize further growth or should I store them differently? Or take them to a professional?

    - Craig Lee
  • Question asked 2016-11-02 12:53:35 ... Most recent comment 2016-11-02 13:35:00
    Acrylic Drying Oils
    Question
    Can matte acrylics can be used (ie thinned with matte medium) under an oil paint film, ie as an underpainting/ebauche layer?
  • Question asked 2016-11-01 15:34:30 ... Most recent comment 2016-11-01 20:45:00
    Question
    Under what heading would oil paint questions be under?
    Steven Lewis
  • Question asked 2016-10-29 05:26:54 ... Most recent comment 2016-11-01 14:45:00
    Varnishes
    Question
    How do I remove Damar varnish, oil panting on linen, 28 years ild
  • Question asked 2016-10-31 06:10:06 ... Most recent comment 2016-10-31 09:10:00
    Flexible Supports Gilding Other Sizes and Adhesives
    Question
    I am about to start oil painting on canvas with gilded areas (gold leaves) and would be thankful for any advice when it comes to this, especially when it comes to the longevity of the gilded areas. I had previous experience in gilding hard surfaces (traditional Byzantine orthodox icons), but never worked with gold on canvas.
    To be more precise, let's start with size/mixtion. I am using Lefranc & Bourgeois Charbonnel Mixtion (3 hours). Any thoughts on the quality of that size? Will it become hard and brittle over time and cause the gold to crack due to the canvas' flexibility? I've got advice to apply one layer of size, let it dry out and then apply second layer of it before I put on the gold leaves - is this smart thing to do? Supposedly, this should somehow increase the flexibility of the surface...
    Additionally, I know gold is chemically mostly inert material, but are there any known problems related to the chemical reactions between the gold and oil paints? Should I additionally protect the gilded surface, or the varnish that I'm using is enough (Lefranc matt picture varnish for oils/acrylic)?
    Any tips&tricks related to best practices of gilding the canvas are most welcomed. Thanks!
  • Question asked 2016-10-29 08:45:07 ... Most recent comment 2016-10-29 08:57:00
    Acrylic Art Conservation Topics Varnishes
    Question
    I have heard many variations on this and was wondering if there was any sort of agreement on the varnishing of acrylic paintings.
  • Question asked 2016-10-29 07:59:25 ... Most recent comment 2016-10-29 08:09:00
    Art Conservation Topics Drawing Materials
    Question
    Can you please tell me how to remove small spots of rust left on a drawing that was held by metal bulldog clips?  I'd like to not have to trim the paper.  If left , what would be some adverse results? Thank you.
  • Question asked 2016-10-18 21:55:31 ... Most recent comment 2016-10-20 14:12:00
    Drying Oils Other Varnishes
    Question
    There are several areas on my painting that appear matte and uneven compared to the rest of the composition. I am not quite done painting so am unsure how to proceed...
  • Question asked 2016-10-18 11:03:07 ... Most recent comment 2016-10-18 11:04:00
    Health and Safety Pigments
    Question
    I have been hearing a lot about the toxicity of lead white paint.....but some of my colleagues swear by it. I am sort of torn at the moment...

Secondary Search Results: Answers & Comments

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  • This is a Moderator Answer - Click Here to view the full thread.

    I also have no experience with the Zecchi product or its formulation so I can't comment about it efficacy.

  • This is a Moderator Answer - Click Here to view the full thread.

    If I understand the question correctly, it seems to me that secco painting, as compared to buon fresco, is always applied on a wall that has dried and preferably cured. Therefore, the pH sensitivity of the pigments is less critical than with true fresco (where they are applied into a wet wall of calcium hydroxide which converts to calcium carbonate in the presence of carbon dioxide). Secco paints only need to withstand the pH of their binder and any residual pH of the carbonated lime. The wall would be chemically the same as limestone. As to the suitability of acrylic, it would seem fine. The only issue could be if the acrylic component is high enough this could result in a pronounce sheen. This is really true of almost all secco techniques as compared to buon fresco. Casein and distemper are probably the best in terms of this issue. The continued solubility of animal glue makes distemper a poor substitute in terms of longevity.

    Apologies if I misunderstood your question.

  • This is a Moderator Answer - Click Here to view the full thread.

    Matthew is probably right about the particle size issue

    The comment below was written by Bruner Barrie who runs Sculpture House

    Since there is various type of soapstone or Talc Block that may also be called Serpentine or know by other names it would be difficult to answer this question without more information.  I cannot see why any of the different types might not be used with Gesso although the porosity might be different within the different types. Montana, India African, and Alaskan stones all vary so I would suggest the person take a small amount and mix up test batches and lay around to see what they might like best. That is what I do quite often when trying something new and exciting and it seems to work well in the long run.

    Hope this helps.

    Thanks and Sincerely,

    Bruner

     

  • This is a Moderator Answer - Click Here to view the full thread.

    Traditional burnished gold could only be accomplished with water gilding. This means that it needed to be applied over an animal glue containing ground and usually over an animal glue containing colored bole. This means that the ground must be true animal glue containing gesso or animal glue-chalk. I understand that there are other methods that achieve mirror-like gold effects. Kölner Insta-Clay is one such product. I have never used it so I cannot comment on its efficacy.

    The reason why you cannot burnish oil gilding is that you are actually burnishing the ground and bole, not the gold.

    When oil gilding or polymer gilding it is usually best to apply some sort of sealer to cut the absorbency. This prevents having the gilding fail where too much of the size was absorbed into the object. I know that shellac was often used for this purpose but I would assume that any was approved for permanent work, dried insoluble, and could be applied smoothly and without brushstrokes would work well. Having it in a spray can would be helpful as well.

  • This is a Moderator Answer - Click Here to view the full thread.

    It is not that PVA size in inadequate, it is that one coat is not adequate. Multiple coats should work fine. Acrylic dispersion just seem to accomplish this with fewer coats.

  • This is a Moderator Answer - Click Here to view the full thread.

    Matthew, the same thing can be seen on paintings hung on exterior walls (those that have the outdoors on the other side as compared with interior walls). The movement of moisture through the wall has a major impact on preservation. I have images of a pair of pendant portraits from the 19th century that were painted at the same time and with the exact same materials and techniques. The one hung on the interior wall is in very good condition while the one hung on the exterior wall is flaking and in a poor state of preservation. 

  • This is a Moderator Answer - Click Here to view the full thread.

    Art is only as durable as the collector's commitment to proper display and care. A watercolor needs to be correctly framed and displayed in a location that doesn't excessively expose colors to UV light. The same is true of any painting. Gallery owners have told me horror stories about valuable, important works hung in client bathrooms, over fireplaces or even on outdoor patios. Of course, the artist can't claim, "warranty void if hung in the bathroom".

  • This is a Moderator Answer - Click Here to view the full thread.

    ​Soapstone dust is not a good substitute for calcium carbonate in paints and grounds. The particle size of the dust produced by carving is probably not optimal for paint and grounds anyway. I would just dispose of it (wearing a particle filter mask), and if you want to use hydrated magnesium silicate/talc in the studio for inks or ceramics, select a cosmetic grade that is finely processed and product free of asbestiform particles.

  • This is a Moderator Answer - Click Here to view the full thread.

    Let me first say that watercolors can be a very permanent medium, especially if they are created and treated in the manner that you suggest. I would bet that this is not the norm. One could also say that most oil paintings are not created and treated in an optimal manner, as well.

    There are reasons why many commentators seemed to elevate oil paintings above watercolors in terms of longevity. The first is due to the nature of the paint. Historically, watercolor manufacturers were more likely to include more fugitive pigments in their watercolor line than their oil lines of paintThis was backwards thinking on the part of the art materials manufacturers. The gum Arabic binder in watercolors is very minimal and does not really surround and coat the pigments in the same way that oil or acrylic dispersion binders do. This means that the pigments receive the full force of visible and UV light. Pigments that are barely suitable in oil are outright fugitive in watercolor. The other binders are more fully covering and absorb some of that energy. The presence of a varnish creates even more of a barrier. You did address this and included only permanent pigments in your ideal description.

    The paper is another source of sensitivity in watercolors, even the highest grade cotton rag paper can suffer photochemical degradation. Again, you mention the use of UV blocking glass, which would prevent this. Canvas is usually made from cellulose as well, but in traditional painting, this is covered with a ground and the paint, blocking this radiation.

    Finally, the absorbent nature of a watercolor painting means that dust is easily trapped in its surface and the water-soluble nature of the medium complicates cleaning. And again, your ideal watercolor addresses this.  So if the one takes the precautions you describe, watercolor can be very permanent.

  • This is a Moderator Answer - Click Here to view the full thread.

    ​Hi -

    If deciding to paint on metal with acrylics the most common choice would be aluminum in order to avoid the problems associated with more corrosive options, like steel or copper. Along those lines, the best introduction to the topic would be an article Mark Golden wrote for our Just Paint newsletter:

    http://www.justpaint.org/painting-on-metal-an-introduction/

    as well as this one on preparing Dibond, an aluminum composite panel:

    http://www.justpaint.org/painting-on-dibond/

    Especially if going outdoors, and/or choosing to work on raw aluminum, you are best off preparing the metal with high end commercial primers made for that material. As the article lays out, for aluminum the best options will involve three steps of degreasing, etching, and then application of a conversion coating. Because this involves a lot of work, we strongly recommend going with a pre-prepared aluminum panel such as Dibond, which comes with multiple surface coatings - including clear coats that preserve the look of brushed raw aluminum - which will allow you to paint on top of them will far less prep. In fact you could get away with simply scuffing the surface, cleaning with isopropyl alcohol, then using an acrylic gesso if painting indoors or using something like Sherwin Williams' DTM Bonding Primer or XIM's UMA. Both mentioned in the articles above. After that, then you can proceed with acrylic paints as you would normally. If going outdoors, you would need to be more selective about which colors you use. Here is a list we give for outdoor murals which are the most durable and lightfast in exterior conditions:

    http://www.goldenpaints.com/technicalinfo_murals#goldenSuggestedColorList

    While the list is based on testing of our own paints, in general the recommendations should hold for most other brands as well.

    Once done, then you should protect the piece with a removable varnish or topcoat. If going outdoors, the gold standard would be a two-part automotive urethane, which an auto body shop can apply. If that is not an option, then a solution acrylic varnish - such as our MSA Varnish or our Hard MSA Topcoat - would be alternatives. Liquitex's Soluvar would be a similar choice. However, none of these are as physically durable or chemically resistant as the auto clear coat. If the piece is indoors, then your options are broader and even a water based acrylic varnish would be a viable option.

    We hpe this is helpful. In truth a lot depends on the particulars of the piece - whether indoors or out, - and your expectations about longevity. If the piece only needs to last a decade or two, that is different than wanting something that is permanent. Even the best metal sculptures outdoors - including a lot of Calders - end up being regularly repainted because the environment is just so challenging. But indoors your chances for the initial coatings lasting a long time are much better.

    If you are planning to use a different type of metal, or having further questions, let us know.

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    ​Yes I think that is probably correct...at the moment there seems to be little known regarding a) the precise characterization and b) quantity of additive(s) being used in this particular brand of "oil paper" to render it suitable for oil painting. I will send an additional query to the scientific community to see if there is an off chance that someone has analyzed one of these papers but as they are fairly new to the market I am not hopeful on this matter. I can comment however on your musings re: Jan van Eyck. While A. P. Laurie's writings are indeed valuable and interesting to read, unfortunately I would not place a whole lot of faith in his conclusions regarding Old Master painting practices. We address this issue in our resources section in a document called "Myths, FAQs, and Common Misconceptions" (particularly in No. 8 and 9). Today we do know lots more about Jan van Eyck and Flemish painting technique and there is little evidence to suggest that there was a systematic use of distemper (glue-based) or tempera (egg-based) underpainting to prepared panels before applying oil (actually "gesso" would be an incorrect term here as that specifically refers to the use of calcium sulphate or gypsum....the Northern European painters at that time used chalk and glue for their grounds). But I do understand your point in including this specific reference as it relates somewhat to the topic of the thread. What appears to be a typical Flemish technique is to first apply an ink underdrawing over top of the chalk-glue ground (which MAY have had additional layers of glue applied on top of the ground to cut the absorbency). This was usually then folllowed by a pigmented oil-containing layer (which the Italians would later call an "imprimitura" layer). We do know of a few instances where a layer of unpigmented oil was applied either over the chalk ground before the underdrawing OR more commonly over the underdrawing. This was then usually followed by layers of oil paint. Researchers have reported a handful of cases where egg tempera was used as a full underpainting before oil colors were used to cover the entire surface. However, much of this research was done quite early on (even though it was performed WELL after Laurie's time) and even these results should probably be re-assessed. 

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    Really, there are no good reasons to use common cardboard. Acid Free blue board is vastly preferable for the reason enumerated above. I have a query into another moderator for more info about your question posed on the other thread.

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    ​Hi - We do not know what is in the Zecchi product and would encourage you to communique with them directly to understand what their thoughts are about the suitability of their paints for buon fresco. I can say that in general acrylic binders are quite resistant to alkaline surfaces and materials. In fact acrylics are often included in plaster recipes to increase chip resistance - such as our own Acrylic Modifier for Plaster. But it is also important to know that the acrylic binder does not on its own protect pigments that might be alkaline sensitive - so pigment selection remains critical.

    On that front, traditionally all organic pigments, including synthetic ones, would be avoided. However we are also unaware of any rigorous testing that directly shows if this is true for all organics, without exception - including the Quinacridones, which are often listed as alkaline resistant by the manufacturers. The real question might be just how resistant are they, since fresh lime plaster would an extreme case. In this regard, the RealWorldColor is interesting since the author's own testing appears to show the Quinacridones as stable for fresco. If wanting to be more adventuresome, and willing to do additional testing on your end, you can certainly evaluate the palette given here:

    http://realcolorwheel.com/fresco3colorchart.htm

    Just keep in mind this comes with no guarantees that your own experience would be the same, so do as many trials as you can.

    Obviously the safest method is to stick mainly with a truly traditional, well-proven list of colors, such as this one:

    http://www.noteaccess.com/MATERIALS/FPigments.htm

    This can be safely supplemented with any other iron oxide pigments.

    Hope that helps.

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    The nice thing about using solvent borne acrylic as a size is that it does not cause unstretched paper to buckle like acrylic dispersion sizes can.

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    Also I have been thinking about what would be the best replacement for hide glue and am becoming convinced that solvent acrylic is best, since it lacks evaporation holes and I use it, when I am working on paper with oil. Another question that comes to mind is what goes under the paper. Artists working in oil tend to not want to use mats, glazing, and/or mounting to Dibond and I often wonder why. Hard mounting, before the painting is done can be done with acrylic gloss medium, but how to do this, when the painting is done, should include some release layer and that is what I am working on these days. As I said, before, I think acrylic is more flexible and clear than either PVA or even EVA and I have found it to be a glue that will even bond to the surface of an oil painting. I am thinking of polyester felt or Volara as a release material and will let you know how my testing works out, but I see this as an issue that will continue to come up.

    Hugh Phibbs

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    Paper is a wonderful substrate for art and watercolor paper has cotton and animal glue to protect the cotton fibers, but that glue is not enough to keep oil media from staining and oxidizing, over time. I first heard that Arches was making an oil paper, when I was teaching in Paris, but I have not been able to learn what is added to the paper to block the oil. Their literature stresses the idea that the paint will have some grip on the surface, avoiding the “crawl” one sees, when oils are applied so some slick surfaces, but the penetration of the oil must be limited. I have worked on Arches cold pressed, applying acrylic, in varying thicknesses, over which I then applied oil, and my experience showed me that a stain of acrylic did not prevent oil penetration and that a film of acrylic was needed to get to a point that oil did not show up on the verso. Acrylic medium can be applied to watercolor paper, to prepare it for oil and one can assess the thickness needed by looking for oil penetration. Acrylic should be more flexible and clearer than PVA, but with any aqueous dispersion, that product should be applied, allowed to dry, for two weeks, and then the dry film should be washed with water, to remove the surfactant that has leached to the surface. If tooth is desired, a matte acrylic and be used and the paper can be wetted, or a wetting agent (ox gall or alcohol) can be employed, but they would complicate the chemistry. 

    Hugh Phibbs

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    ​Hi there!  I'm curious, when you say "sizing" what process are you using?  Sizing can refer to a few different processes, and I want to make sure I understand how you are working. 

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    ​Yes this is true (that graphite does NOT migrate through egg tempera films). Again I suspect that this notion has been propagated by the occasional scenario of the paint layers becoming more transparent over time thereby making it SEEM as if the underdrawing doen in graphite is "migrating" up through the paint layers (when in fact it is simply becoming slightly more visible). While this tends to happen more readily in oil paint films it certainly can happen to a certain extent with egg tempera depending on many things (the particular pigment(s) present, the thickness of the paint layer, etc.).

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    Brian, We've been tripping over each other lately! I'm glad if I added something useful.

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    ​Ha

    Matthew, you posted while I was editing my post. Anyway, multiple voices are always better. Thanks for the commentary on the health issues. I had completely missed that in my response.

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    Hi

    The medium you describe was used by many, many painters in the 20th century and is identical to the medium Ralph Mayer suggested for glazing in oils (although his recommendation contained cobalt drier as well). Today this medium is not considered as benevolent as it was in the past. The large percentage of soft dammar resin can contribute to a paint film that is sensitive to the solvents used to remove degraded varnish in the future. It also contributes a degree of brittleness to the paint. Stable paintings can be made using such a medium but it would need to be added in very small proportions as compared to the oil paint. In practice, this is unlikely and it is best to avoid mediums that contain soft resins. Finally, the dammar is the reason why you have required turpentine rather than a less noxious solvent like a highly refined zero-aromatic odorless mineral spirits. Dammar is not soluble in these solvents and requires either turpentine or a mixture with a high proportion of aromatic hydrocarbons.

    There are some other alternative solvents but they tend to smell just as noxious during longer painting sessions. Some of the claims of lower toxicity for some of these may actually simply be the result that they have not been tested as extensively as the more common diluents.

    So, what you need is an oil medium that does not require turpentine (or aromatic hydrocarbons) or soft resin.  Stand oil diluted with a solvent is perfectly fine in terms of stability. It may be less desirable in terms of paint handling. It really depends on what you are after. I have found that this mixture really levels paint strokes and can contribute a greasy effect rather quickly. It is sticky without having the “feel” that your old medium had due to the resin. Linseed oil and solvent is workable as well although its “feel” is also very different from what you are used to.

    I personally have not liked the handling of gelled alkyd mediums but others really love them. I have found that the fluid alkyd mediums more closely resemble the older mediums like the one you describe. You may want to thin them with additional OMS if you use larger amounts of medium as you suggest. You could even use one of these as a component of a three-part medium by substituting the alkyd for the damar and OMS for the turpentine. Finally, have you tried using any of the newer solvent free oil mediums? A Google search should yield a number of these offered by different manufacturers.

    Sorry if this is a less than satisfactory answer. Perhaps others here have a different or additional take on this issue.

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    There are health risks associated with exposure to Pure Gum Spirits of Turpentine, including respiratory problems and allergy-like sensitivity. Many experienced painters with a long history of turpentine use have migrated to clean Odorless Mineral Spirits. This type of solvent is not completely without risk, but OMS does not induce materials sensitivity. OMS also evaporates at a slower rate than turpentine, so the buildup of vapor is not as rapid. Even high quality art supply brands of OMS are very economical. Of course, this is still not solvent-free painting. Also, the paint doesn't behave quite the same with OMS compared to turpentine.

    Damar varnish also contains turpentine, so you may want to consider replacing that component of the medium with walnut alkyd medium or solvent-free alkyd gel. These do cost more than damar (especially homemade varnish) but they do offer very nice handling and drying properties without hydrocarbon solvents.

    Another reason to consider replacing damar in your studio is that a paint film containing significant amounts of damar can remain soluble for a long time, making cleaning more problematic. Since you mention that you use large volumes of medium, solubility and other drawbacks of damar (e.g. darkening, embrittlement) may be a concern.

    The vegetable oil components of your medium don't generally present any particular health risk. Linseed, stand, safflower, poppy and walnut oil are all free of hazardous vapors, though some do find the smell of linseed oil unpleasant. All drying oils (including cooking oils) can spontaneously combust from buildup of heat from oxidation, when oil-soaked rags are left balled up. Rags can be left flat to dry before disposal, or immersed in water in a lidded metal can.

    Finally, when solvents are present in the studio, adequate ventilation is essential- there's no substitute. Make sure air is moved and replaced, not just moved around with a fan.

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    My thoughts are simply that such canvases are unsuitable for anything other than the most disposable sketches. The problem with this is that you never know when an expected humble sketch turns out to be very successful. It would be far better to buy some better quality stretcher bars and a length of primed substantial canvas (rather than the overly thin cotton canvas usually encountered with general pre-stretched, primed canvases). With these you can create your own canvases. That way you can always easily remove and dispose of unsatisfactory paintings and have a quality product if you are pleased with the result. You could also simply purchase higher quality pre-stretched/primed canvas by a reputable canvas supplier.

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    ​I happily stand corrected :) One of our moderators Dr. Greg Smith has identified a resource that does indeed possess such images. He is looking into scanning the photos for you...but in the meantime you can try to locate the reference yourself should he prove unsuccessful: Burnstock et al "A pilot application of SEM and hi resolution x-radiography for the conservation of paintings" in Historical technology, materials, and conservation: SEM and Microanalysis 2012.
    This was the conference held at the British Museum, and the proceedings were published by Archetype.

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    ​Very intriguing question for sure :) So first of all I am assuming you are after VERY particular SEM images. Just so other readers have a bit of background, SEM-EDS can be used to generate two types of images....one that can show the distribution of certain elements across the surface of a sample and another that can show the morphology/topography and, in some cases, the general composition of a sample. I am assuming that you are after the latter. With paint samples I am afraid this is a bit of a problem as most of the time paint samples are mounted in a specific manner that involves encasing them in a polyester-based resin (or another type of hard resin that can cure in 24-48 hours). The resin is MEANT to penetrate all of the interstices of the sample to provide a smooth even surface when the paint sample is polished down and to secure the paint in place (SEM-EDS is performed under a vacuum and it would be a sad day if the sample were to get sucked up into the instrument....that would cause damage that can get rather costly). So you would need to find SEM images of paint swatches that have somehow been glued down or afixed to a surface...and then the images would have to be collected in secondary mode of the exposed surface. To be honest I do not think this has been done. But what I can do is put a query out there to the conservation science world to see if I am wrong about that.

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    Hi again -

    Please link to my reply and share with the Facebook group you found this discussion as I would not want the misinterpretation to stand without comment there as well.

    Thanks.

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    ​Hi -  

    My first and most immediate response was "whoa whoa - where you are getting that interpretation!". First, nowhere in the article do we mention Gamblin, and that is important as we do that on purpose and on principle as we would never directly comment on another manufacturer's products, especially in a way that might be construed negatively. When we use products from other companies we do so with an eye to simply understanding how they work with our own products, as we assume that people will mix and match out in the world and its important for us to be aware of those things. But we do not mean those tests to be evaluations of the products used within that manufacturer's own product line. We are not set up and it would be anathema to us to present our testing as a form of third-party consumer product testing for the industry. Finally, we also have great respect for Gamblin and have had a long relationship with Bob and would never imply that they made anything other than professional products.

    Second, here was our summary about PVA Size up near the start of the article:

    "PolyVinyl Acetate (PVA)

    While pH-neutral PVA adhesives have long been used in conservation and the book arts, some manufacturers now provide PVA-based sizes for use in preparing canvases. These should adequately protect fibers from the oxidizing effect of drying oils and prevent strikethrough. In our own testing, the number of required coats to achieve this was varied, with one coat clearly sufficient for a faster drying, alkyd-based ground we tested, while a minimum of two coats were required for all the slower drying, oil-based products. Always consult with the manufacturer and check for your own application to see what is optimal."

    Nowhere do we imply that a PVA Size is not a suitable and viable system. What we did find was that if paired with a fast drying alkyd-based ground, one coat was sufficient and worked well. It was with slower drying very traditionally formulated grounds, such as our own Titanium or Lead Oil Ground, where we saw strikethrough as the oil had days to be able to work its way down and through - and oil molecules are rascally things that are great at penetration, especially if given the time. A faster drying alkyd ground, on the other hand, sets up rapidly - often overnight - and so there is less chance of that happening. And even in the above case, applying 2 coats of the PVA size reduced strikethrough to a very minimal level, and I could easily imagine a 3rd coat would have taken care of that. But the main thing to keep in mind is that when pairing products, especially if choosing a size from one manufacturer and a ground from another, you need to do some testing to see what works as directions are almost always assuming the best process for use within a manufacturer's own system. So by all means pick and choose and combine, but when doing so you should assume that some adjustments to the instructions might be needed.

    Ultimately PVA Size is a well tested option that has a lot of use and acceptance in conservation circles and we think it is a perfectly fine option. The one we tested was quite flexible, especially if comparing to the absolute gold-standard for stiffening, rabbit skin glue, which is what we aim for duplicating when developing an option using our acrylic sizes. I am not sure, to be honest, if a PVA could be made stiffer, but I would not avoid using PVA Size on that basis alone if it is something you like using. It did leave the canvas feeling very supple - almost like it had no coating - and that has a certain allure.

    In the end I think you can feel that the Gamblin product is a professional one and I would not in the least disparage the company or feel that they in any way misrepresented it. They have had a long relationship with folks at the National Gallery - we share in the same contacts - and the Canadian Conservation Institute has done some of the most extensive testing of PVA Sizes around. They literally 'wrote the book' on the subject:

    https://www.iiconservation.org/node/877

    http://www.tandfonline.com/doi/abs/10.1179/2047058414Y.0000000129?scroll=top&needAccess=true&journalCode=ysic20

    https://pub.cci-icc.gc.ca/resources-ressources/publications/category-categorie-eng.aspx?id=20&thispubid=533

    and I would have no doubt that they reached out or worked with folks there when developing their product.

    Hope that helps give you some confidence. Pairing a size and ground and getting a system that is right for you can take some fiddling and testing. And never hesitate to reach out to Gamblin directly if you need assistance or have questions with their products. They should be very helpful based on my own interactions with them. And if you have questions about something we wrote - and in this case something I did - please reach out to us directly if needing clarification as well. We are always happy to do what we can.

    Thanks.

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    I have very little to add here other than to mention that in addition to the difference already mentioned, quinacridone red is also a little less transparent and, therefore, lighter in mass tone than either alizarin or rose madder lake. As stated, though, these small differences should not stop one from using the vastly more permanent alternative for anything other than a historical reconstruction.

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    Hi Bob -

    As you might imagine this topic can have many layers of complexity so will try to address some of the basic issues. I also have never done testing on NR9 - it is not a pigment we use - but can share results from Alizarin Crimson which is generally seen as the weaker between the two. As you intuited the lightfastness for all these colors would be worse in the tint and in fact lightfastness ratings are based on the performance of a specific tint let down with titanium white until you achieve 40% reflectance in the wavelength of maximum absorbency. For a sense of what that looks like, and a description of the lightfastness test procedures, see the following article:

    http://www.justpaint.org/alizarin-crimson-now-you-see-it/

    and for how to interpret those results based on what is called delta E, see:

    http://www.justpaint.org/delta-e/

    Many but by no means all lightfastness II and III colors can perform markedly better in the masstone. A classic example would be Alizarin Crimson, and by extension NR9 as well. See the following where we show some actual results:

    http://www.justpaint.org/alizarin-crimson-now-you-see-it/

    As you can see the deeper masstone in the oils holds up quite well - it actually barely budges and on its own would be considered  a strong LF I. But as a tint there is a major bleaching out. Fanchon Red is similar in this way, but not so much with PY 3, where masstone and tint scored very close to a LF II.

    I should also point out in the Alizarin Crimson piece you can see how effective a UV protective Varnish was in preserving what would otherwise be a light watercolor wash. Or see the results of applying a varnish to fugitive dye-based inkjet prints towards the end on the piece on Lightfastness. That said, applying a UV varnish or UV filtering Museum Plexi or Glass, does not always work that effectively. If a pigment is sensitive to light within the visual spectrum then the varnish and glass with have far less impact.

    In truth, outside of historical interest, there really are few reasons not to seek out more permanent alternatives that would be safer to use. For example, Pyrrole Reds are rock solid and can replace napthols, while Bismuth Vanadate lines up fairly well against PY3, and finally PR177 is much more permanent that either PR83 or NPR9, but is not a perfect match being a bit cleaner and higher Chroma. However, if wanting to use them, keep them as close to full strength as possible and applied generously, and if aesthetics and finances allow, use a UV protective spray or UV Plexi at the end.

    Hope this at least answers some questions.

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    ​Hi Ron -

    You'll be fine.....always a pleasure to chime in.

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    This is always one of those difficult questions to answer. As you gather from your own experience the risks are very minimal and usually nothing happens, and because of that, I don't want to raise incredible concerns. The odds of a problem occurring are probably very low. But.... (stalling as I put on my technical hat).......can I imagine scenarios where something occurs? Sure. Higher humidity could slow the evaporation of moisture enough that the oil paint does not penetrate as deeply, and so develops less mechanical adhesion. But I think it would need to be extreme to really be a major issue. Also, keep in mind that acrylics are alkaline in their wet state - and contain a small amount of ammonia - so until the majority of the moisture has evaporated the canvas surface could still be alkaline as well. Alkalinity, in turn, can cause the fatty acids in the oil to saponify, which could also impact adhesion. Because it is just good advice to keep ammonia and oil paint away from each other, we generally prefer giving the surface extra time to fully dry and be truly pH neutral.

    That said, we have never seen the above issues come up in our testing, nor in all the years we have fielded calls and inspected canvases. So my guess is that it is extremely rare and requires something of a perfect storm. But......tech hat again......perfect storms DO happen, and if it happens on a really important piece, that can be heartbreaking.

    In the end, the 24-48 hrs. you are waiting is shorter than the 3 days we recommend as a minimum, but we are also erring on the side of caution and trying to give advice for people living in a lot of different environments. Also a brushed on acrylic layer is just so thin that in truth the majority of the moisture will easily be gone in that initial timeframe. At the very minimum, however, I would say do not paint on any water-based coating if the surface still feels cool or clammy, as that would clearly indicate a good deal of evaporation is still taking place. And as I always like to note, if you can prepare several canvases at once, then even if you use one after a day or two, the others almost invariably will sit around for a week or two.  

    Hope the above is helpful. In the end it is all a matter of risk management. If you always gravitate and want to adhere to the absolute best practice, and have minimal to no risk, wait two weeks. If a small amount of risk is tolerable, wait 3 days. If you feel okay pushing that envelope slightly, then your 24-48hrs is likely fine. It reminds me a bit of the quandary whenever reading medical statistics. If doing something increases the likelihood of an illness by 400% that sounds shocking, and one quickly promises to amend their evil ways, but if that translates to actual incidences going from 1% to 4% that might seem okay for the tradeoff, and french fries it is!

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    Matthew, no problem, more responses are always better that fewer. We tend to focus on different aspects of the concept and the combination of replies is always richer than would be the case if only one person responded.

    To the OP

    Drawing into thicker paint should insure integration and be stable. Additionally, even if you do not follow this precaution, your work may still remain relatively stable. Drawing into more substantial layers of oil only ensure this.

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    Sorry, Brian, I must have been writing while you clicked "post". ​

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    Once a graphite sketch on the ground is integrated into a dry paint film it should be stable, unless the graphite application is so heavy some unbound, loose particles remain. If graphite lines are in the top layers, , the varnish can mix with the graphite particles, and consequently these marks can be lost if the varnish is removed.

    Graphite particles don't migrate through a dry oil paint film, but the material is denser than charcoal and can mix readily with paint, staining light colors in the first application. Also, as paint ages and becomes increasingly transparent, marks underneath may become more visible.

    We know graphite doesn't migrate within a paint film because Albert Bierstadt used a graphite-based oil ground for many of his paintings and, while the pictures may have darkened slightly, the ground color has not asserted itself through the actual paint. Unfortunately graphite primer proved not to provide a very good surface for oil paint adhesion, and Bierstadt eventually switched back to lead white grounds.​

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    Like so many things that come up on this forum, it depends on a number of factors and just what you mean by durable. Graphite in itself is very stable so that is not an issue. Probably the biggest factor here is just how much oil paint are you drawing into. If the paint is substantial enough that the drying oil saturates the graphite particles, the graphite would be incorporated into the paint and would be quite stable.

    If the particles are not incorporated into the paint, the particles would rely more on mechanical adhesion. This is itself is not a deal breaker. There are many, many paintings where contours have been reinforced with pencil. The only real problem is possible smearing on one hand or removal during future cleanings on the other. You mention that the work will be varnished, this means that the first potential issue would not be a problem. However, the graphite could possible be displaced when and if the varnish is removed at a later time. This is in no way a certainty. Pencil was sometimes used to depict the rigging on maritime paintings. I have observed some examples where the graphite lines have resisted restoration and others where the rigging is partially removed. To be fair, though, I have also seen plenty of instances where rigging executed in oil paint  (or oil with an addition of varnish) has been removed by the insensitive cleaning of an ill-trained restorer.  

    I hate to keep giving less that definite answers, but “it depends” is often the only true answer.

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    ​Leslie is an amazing force unto herself and is a major reason why I transitioned from fine art to technical art history and eventually art conservation. In fact, it was my purchase of her "unpublished" doctoral thesis in 1999 that solidified my decision to enter the conservation field.

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    ​Probably the best way to answer this is to introduce you to AATA. Do a search for Leslie Carlyle. http://aata.getty.edu/Home

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    Thanks all.

    As an interesting connection to this dialog, I actually spent a summer working with Leslie Carlyle on her HART project in Amsterdam (2005) hand grinding, using a granite muller and slab, hundreds of lead white paints with additives/other pigments added in 5% incriments (barium sulfate, etc) in various mixtures of oils in 5% stepwise additions (eg, cold-pressed linseed oil 95% 5% poppy oil, 90% CP L Oil 10% poppy oil, and so forth). We took these to a few research facilities and paint manufacturers to measure rheology. The last couple of days were spent painting out all of these on multiple substrates. Leslie has used these, and many others, for her years of subsequent research.

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    I agree with both Brian's and George's assessment. It is also important to mention that various form of refining (including less industrial versions of both acid and alkali processes)  were carried out in the past 

    (see the section on Refining linseed oil paints starting on pg 14 of Analytical Chemical Studies on Traditional Linseed Oil Paints 

    https://pure.uva.nl/ws/files/3716376/20662_Thesis.pdf

    and that what passes as 'cold pressed' both historically and today is not a singular standardized product. While starting out as a raw expeller pressed oil - without the use of heat or chemicals - it ultimately undergoes any number of refining processes that historically changed over time and had wide regional variation. So that would complicate any claim or study as you would need to define what you are comparing to. Also remember that even the genetic make-up of flax had changed over time and it is not at all clear that the fatty acid profiles of todays' oils match that of the past, since strains have been continually optimized and crossbred to have better resistance to disease, draught, yield, etc.

    That said, we continue to study this area and are open to the possibility that older processes of refinement might produce some interesting differences in handling and drytime, as Leslie Carlyle's work on the historical reconstructions of lead white using differently processed oils seems to point to. But currently we have not seen any evidence that structurally cold pressed linseed oils are superior and indeed the alkali-refined oils we use seem more consistent and less variable in its batch to batch qualities.

    Hope that helps. 

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    ​I have been scouring literature on the differences between non-refined (cold-pressed) and refined oils for many years, and have not found any that informatin that would support claims attributing improved mechanical strength of paint films due to the refinement of the oil. What is well-known is that refined oils contain less impurities so that they tend to yellow less and dry faster. However, this subject has not been studied, so there is no definitive answer.

    As has been found in studies by Marion Mecklenburg and others, is that the mechanical strength of paint films is largely due to the pigment, such as lead white. Whether the state of refinement has any effect on this is not clear. However, understanding the nature of the impurities in oils makes its unlikely that they would contribute positively to the mech8ca strength of the dried paint film.

    In one study we conducted, however, we found a difference in the tensile strength between types of oils, such as walnut and linseed oil—linseed oil exhibiting higher tensile strength than walnut oil.

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    I am not a commercial paint maker, but this is of interest to me. The bias that you mention has been around for quite a while. The idea is that while the alkali process removes more organic impurities, it may leave some residues or somehow weaken the oil in a deleterious way.  Some would suggest that the refinement weakens the oil in some manner creating a product that is lighter and less prone to yellowing, but not as capable of adequately binding a given volume of pigment. We first have to ask, how could an oil that contains more impurities be superior? However, this was certainly true very early on when oils were crudely refined leaving residual acidic or alkaline components. This was compounded by the fact that the oils that were generally refined by these processes were those of the coarsest extraction and were intended for only the crudest uses. This is in no way the state of things today.

     Linseed oil refinement is a carefully controlled process, which allows for cleaner and purer oils than available previously.  We do have evidence that modern quality refined oils yellow less than cold pressed oils. In the recent past, the only real benefit to cold pressed linseed oil was its use in grinding oil colors (as opposed to use in mediums/commercial oil varnishes for wood, etc. where this was less valuable) due to its high acid number. While this does contribute a bit to yellowing, it does allow for the creation of a paint that requires substantially less oil than paint made with linseed oils of lower acid numbers. This is a non-issue today since alkali refined linseed oils are available in any acid number that is required. Additionally, If you read mid-20th century literature on the subject you get the impression that oil paints made from non-cold-pressed oils were more likely to exhibit a suede effect. I am firmly of the opinion that this effect was the result of the commercial use of stabilizers, like wax, aluminum stearate and aluminum hydroxide, which created a paint that was unnaturally short and would not level, unlike more simple oil paints that lacked such fillers/stabilizers. Hand ground paints were less likely to contain these fillers, and therefore, did not exhibit that defect. This dichotomy contributed to the deification of cold pressed oil well beyond the virtues of the material…or at least this is my take

    We have a few paint makers on our moderating board and industry cotacts and I look forward to their responses to this thread.

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    ​Thanks George.

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    There should be no problem in terms of paint adhesion/etc for you to paint directly on the shellac sized panel. The only issue would be the color of the panel. Depending on how dark the wood is, this would be visually similar to painting on a mid-toned or even dark colored ground. We know from examining old oil paintings that oil paint can becomes more transparent overtime. This is mostly, but not completely, the result of a chemical change in lead white and even zinc white paints. Thinly painted lighter or even mid-valued paints can become darker because of this increased transparency. This sometimes resulted in an exaggerated contrast effect where the darks became slightly darker, the midtones disappeared, and the thickly applied highlights remained light. Othertimes, it caused an overall lowing of the value and intensity of the painting.

    We are not sure if paintings made with titanium white will exhibit this increased transparency of time but it is unlikely to do so to the same degree. We now know that oil painters should avoid the use of zinc white for a number of reason. I am also definitely not suggesting that oil painters should avoid lead white. It is really the best oil paint that we have in terms of preservation. Additionally, there are plenty of paintings from the 17th-21th C. where that artist left portions of their wooden panel exposed for a specific effect. We just do not know the degree to which these have shifted overtime. What I am suggesting is that a painting executed on a darker color (like could be the case with shellac sized wood) should not be painted too thin if the artist wants to avoid possible changes overtime.

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    Calcium carbonate derived from different mineral sources behave differently in paint. The material can be ground from limestone, a sedimentary rock formed in sea beads or alluvial deposits; or marble, which is limestone that has undergone heat and pressure below the earth's crust; or chalk, a light, low structure material normally associated with the sedimentary deposition of the shells of such minute marine organisms as foraminifera, coccoliths and rhabdoliths. The particle structure and chemical behavior of these variations of calcite all differ slightly.

    The particle size and shape of calcite in regards to the behavior and performance of paint are important for several reasons. One is the viscosity of the paint, which is related to the volume occupied by the dispersed solids within the paint vehicle.

    Another consideration of the influence of particle size and shape on the behavior of paint is the surface area of the particle. The amount of paint binder required by a pigment to form a paste paint is called its oil absorption (OA) number. The greater the surface area of the particle, the more binder it demands to make into a paste or flowing paint. Synthetic (precipitated) calcium carbonate that consists of 0.05 micron needle-shaped particles has more surface area than the particles of ground limestone of the same size, which have simple structures resembling rhomboidal crystals. Because of the complex surface of the precipitated calcium carbonate, it will tend to scatter more light and consequently appear more opaque than the ground limestone particles. However, it is likely that this precipitated calcium carbonate will consume considerably more binder than the ground limestone.

    Selecting the right type of calcite, taking into consideration particle size and shape, brightness, chemical constituents, and surface treatment are important factors when it comes to making paint or oil painting mediums.

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    If you are diametrically opposed to the use of alkyd mediums despite their good track record, there are a couple of options. Choose only paints composed of fast drying pigments (lead white, umbers etc) or the judicious addition of driers.  I am adapting one of my responses to another thread as it is applicable here.

    I generally do not recommend that artists add driers to their paints and mediums because it is way too easy to add more than necessary and risk compromising your paint film over time. If you performed systematic tests and only added just the amount necessary to make a paint that dries in a reasonable amount of time (a couple of days) this should be safe. If it were me, I would make up a batch (eg 8 oz) of your chosen solvent (eg odorless mineral spirits) and add a few drops of drier. Then add this to a blob of paint diluted in the manner that is typical for you. Test how many days this takes to dry. If it is still too long, add another couple of drops and try again until you figure out the proportions necessary to create a drying rate that meets your requirements. Do not add more than necessary.

    Others may have additional thoughts.

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    First, shellac would not be my first choice for a size for wooden panels but it should be perfectly serviceable. It does benefit from being delivered in a non-aqueous solvent. This means that the wood will not have its grain raised or issues of warping caused by the application of a shellac size. A size should never be applied so thickly as to create a discrete layer and certainly not a glossy surface. Any size applied too thickly will cause problems with adhesion (actually this is less of an issue when painting acrylic dispersion colors on acrylic dispersion grounds since the acrylic dispersion binder is such a good adhesive as compared to oil paint) . See our section on sizes in our “Resources” section for general issues about sizing.

    If the shellac is applied in a dilute enough state that is cuts and evens out the absorbency of the panel but does not create a discrete layer which would eliminate mechanical adhesion of the ground and paint layers, this should be a trustworthy panel. Whether these specific panels are “acceptable and durable” would relate to the above as well as what type of panels they are sealing with shellac. No size is likely to make a junk panel acceptable.

    There is actually a long history of the use of shellac as a preliminary application before oil paint in the house painting trade. I seem to remember reading a house painting manual from the early 20th century where it said to, “give the wall a good drink of shellac before painting in oil paint,” or something to that effect. I just checked and R. Mayer also mentions this reference.

    Now, the above is specifically about the use of such a size under an oil ground and oil paint. I can see no reason to use a shellac-sized wooden panel for subsequent acrylic dispersion grounds and paint. In that case, it would make more sense to size the panel with acrylic dispersion medium or perhaps PVA size. Animal glue, if one choses to use it despite its reactivity to the environment, should only be used under oil and alkyd layers.

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    For problems with ripples and loss of tension while sizing, I recommend looking at the stretching technique first. If the fabric is losing as much tension as the images in your linked blog post, in my opinion, the canvas may not have been stretched properly.

    Pulling directly across the stretcher frame (the method most artists are taught) can result in uneven tension from spot to spot. It can be challenging to pull with the same amount of force at the corners as in the middle of the bars, even with canvas pliers. An alternate method- stretching diagonally on the bias- evenly distributes tension by displacing the entire network of warp and weft, avoiding tight spots along the span of each stretcher. Also, tacking on the sides of the stretcher rather than the back yields better results.

    I would abandon any further attempt to size canvas off the stretchers, as loose fabric. There's no way to maintain a flat plane or consistent weave pattern this way.

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    The intention is to mix the chalk with oils, correct? Mixing calcium carbonate (or any absorbent filler) with acrylics can significantly affect film strength.

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    Hi Hector

    First, if you are wishing to make a more transparent, yet properly bound paint by adding some form of calcium carbonate, you should really mull the calcium carbonate up into your chosen drying oil to a loose consistency and add this to your paint. Simply adding calcium carbonate to your paint will only make it leaner but would also make it slightly more opaque. Adding too much calcium carbonate in dry form to your paint would result in a film that is underbound, and may be prone to powdering, sensitivity to solvents, and even delamination.

    As to the type of calcium carbonate, while they would all be chemically identical, and would in theory be capable of making a well bound paint that was more transparent, it is really the particle size and shape that contributes interesting handling properties. Only you can decide which are of interest to you. I know that ground calcite is popular but I am not sure about the particular grind commonly used and how that will influence paint handling. I have not personally performed a ton of experimentation using different CaC03 powders to influence handling but I know others have and hopefully they will chime in with suggestions.

    A related question was rather fully discussed here on MITRA and that thread may be of interest to you.

    https://www.artcons.udel.edu/mitra/forums/question?QID=111

    The following thread is only peripherally on topic, but you may find the later portions of interest.

    https://www.artcons.udel.edu/mitra/forums/question?QID=174

    All the best

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    Thanks George. Very cool/ surprising info and results.. Thanks for the follow up and response.

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    ​Based on Ben's comments, we created a test panel on copper substrate with the following grounds:

    1. Rublev Colours Lead Oil Ground

    2. Rublev Colours Lead Oil Paste Ground

    3. Rublev Colours Lead Alkyd Ground

    We also made two samples of lead white dispersed in linseed oil containing paint with free fatty acid (FFA) value of 12 (Sample 1), and another with FFA of 4 (Sample 2).

    In addition half of the panel was rubbed with a fresh garlic clove and allowed to dry before applying the grounds and sample paints.

    As the grounds dried, ground 1 exhibited a green tint on the area not coated with garlic juice, whereas on the area coated with garlic there was no change in color. Grounds 2 and 3 dried without any change in color on either the uncoated or garlic coated areas.

    Paint sample 1 had a slight green tint, but not nearly as strong as the tint of ground 1 on the bare copper surface. Sample 2 exhibited less tinting than sample 1.

    Interestingly, we measured the rate of drying of the paint films on the bare copper and the side coated with garlic, and noted that paint on the garlic dried at a much slower rate.

    Grounds 2 and 3 have FFA values less than 1, whereas ground 1 has an FFA value greater than 4.

    The simple test demonstrates that free fatty acids in linseed oil react with copper to produce a green tint. However, it does not explain the degree tinting in ground 1, since the FFA value of ground 1 is less than sample 1.

    We are investigating this issue further to determine the differences, but in the meanwhile, we are recommending the use of ground 2 or 3 as a ground for copper.

    As an side, we formulated Rublev Colours Lead Oil Ground for porous substrates, such as wood and canvas, but not for non-ferrous metal substrates such as copper or aluminum.

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    Stand oil is not the best choice if you are trying to avoid leveling. Its inherent quality is to level. Linseed or Walnut oil sun thickened mediums, or to a lesser extent, artificially oxidized oil mediums, will be better for this as they tend to set or hold their shape, and set before leveling. Probably the best that I have found for this effect for a black or dark paint is thinning it with a dilute true copal-oil varnish (or possibly a true amber-oil varnish) as they both set quickly and resist the action of restoration solvents in the long run. I mention dark oil paint because both of these will darken substantially and dark pigments will be less effected by this change. I will probably get some push back on this as these materials are controversial in the conservation world for many reasons including brittleness, and yellowing. Used in this way and in fine isolated strokes as described there should be no preservation problems. The problem here is that true Congo, Zanzibar, and other hard copals (and true amber varnish) mediums are either unavailable or very expensive. Really, there is little benefit of these mediums over a high quality fluid alkyd medium for this purpose. I personally find the gelled alkyds less useful for this purpose.

    To the 2nd question, 1:1 mixed with what? 1:1 oil (or even resinous media) to oil paint is way too fat for anything other than special effects, and probably too much regardless, unless you are willing to deal with the eventual strong yellowing  that will inevitably occur. 1:1 oil paint to 1:5 oil solvent may be perfect. It may also be too thin for certain FINAL effects. We need to maintain a bit of rationality in this and you should be able to come up with a sensible ratio.

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    ​Your question is a good one as it is easy to be confused with the term "pine resin" when sifting through the technical literature regarding the analysis of Old Master paintings. The reason why it is hard to get a sense of just what is meant by this term is that it is INTENDED to be a general descriptor; often conservation scientists will use this term when they only have a general idea as to what is detected during analysis. First a bit of background on "pine resin"….I will limit my response here to focus on paintings that are well over 100 years old as this is what you appear to be most interested. Each member of the Pinaceae family (pine, larch, and others) possess chemical markers that can in theory be distinguished using methods like gas-chromatography/mass spectrometry. However, the principal markers (the diterpenoid abietic acids) will all eventually undergo oxidation and ultimately this makes it difficult to identify their origin. So time is really against us here if we are ever to find out for sure the original source of these markers….in general all you can really say is that "pine resin" (likely rosin or colophony) was detected but in theory these markers could derive from other Pinaceae sources as well. Secondly and perhaps more importantly is that there is really no way of knowing at which point these pine resin markers became an integral part of the painting's history. These pine resin markers could indicate that the artist originally added some rosin, colophony, and/or related material to their paints and/or varnish coatings. BUT it is equally possible (and likely) that these markers derive from unoriginal restorations or treatment campaigns. Realize that these materials were traditionally used in varnish coatings, wax-resin lining recipes, and even cleaning formulations in the past. So it is not surprising that we often detect their presence in rather old paintings, particularly ones that have been treated numerous times. So in summary I would say this: our instruments are not quite there in terms of being able to paint a definitive picture regarding what Old Master painters used in their binding media. We can really only say what our instruments detect…the fact that the majority of these paintings have been restored time and time again really complicates our interpretation of the analytical results. We had far more faith in our ability to analyze pictures in this manner some 20-30 years ago but now we know better. That being said we cannot really say that van Eyck and others did NOT use resinous additives. They very well may have….sometimes small additions of resinous components are below the detection limits of our instruments so it is possible that we cannot even identify minute additions. But when we do find these markers it is really impossible to know where they originate from. I do encourage you to continue working and experimenting with these types of resins if you enjoy using them and find that you can accomplish certain effects that are to your liking. I would only ask that you read over our "Mediums and Additives" document in the resources section so that you can take the necessary steps to ensure that your paintings are properly cared for in the future. I hope that somewhat answered your question. Finally, there is a brief outline that describes the origin of various resins and varnishes that can be found on the Kress Technical Art History Website here for addition information.

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    You are very welcome. "Cured" in quotes - just as you did -  is definitely accurate as technically curing refers to chemical changes usually triggered by a substance or energy source. Thus you can have moisture, heat, and UV cured coatings, as well as two-part systems where one part acts as the catalyst. In water-based acrylics, however, the polymer chains are already fully formed and suspended in a dispersion and a more accurate description is that once the water evaporates and the polymers are pushed together, they begin a process called coalescing where the polymers entangle and fuse together into a continuous film. It is that process that continues for quite some time - certainly out to a month or more - but the question becomes at what point can it safely be painted over, and at least for us at Golden, 2 weeks is a good practical timeframe to aim for, with a month being more of an ideal.

    Sarah Sands, Senior Technical Specialist, Golden Artist Colors

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    Just as waiting 6-12 months for an oil ground to cure is better than a week or two, waiting longer after applying acrylic gesso can only help that film fully dry and acquire more of its final, long-term traits. That said, the vast majority of the moisture that will come out of an acrylic gesso film - especially on canvas - will do so in the first 72 hours, which is what we give as a minimum timeframe, while two-weeks is our usual recommendation - but we would not quarrel that, if you can wait, a month is even better. The fact is, there will always be moisture in the gesso - just as there will always be moisture in the canvas and wood we use, as materials reach an equilibrium with their environment. For an acrylic film, in typical ambient conditions, that is in the 11-16% range, which is about the same level of moisture in wood, which of course can be primed with oil-based paints. You can read some of our research in this area in the following issue of Just Paint:

    http://www.justpaint.org/wp-content/uploads/2015/11/jp27.pdf

    As you look at the graphs there keep in mind the “thinnest” film shown is quite substantial - 1/16” - and a brushed on film of gesso, especially on canvas, will reach those equilibrium levels much much faster. And keep in mind, that on canvas evaporation will continue to happen in the rear of the canvas, so even after one paints further consolidation is taking place.

    Hope that helps. On a final note, in my experience, if you prime several canvases and decide to paint on one of then after 3 days or a week, the others will almost invariably sit around and continue drying and by the time they get used a month or more would have passed.


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    Hi

    I know from a forwarded correspondence that your primary issue is the slow drying rate of your oil glazes. I applaud you for refraining from adding large amounts of soft resins to your mixture to speed up the setting of the glazes. This is a common, but lamentable, practice (see our "Resources" section for more info on this subject). I do wonder how much medium you are adding to your paint to create glazes. It is good painting practice to only add enough medium to make a paint that can by physically manipulated to a thin glaze and not to dilute the paint with so much medium that you create a “watercolor-like” wash. I will assume that you are adding a reasonable amount of your stand oil-turpentine mixture.

    My first response to a query like this would be to suggest an alkyd medium. You have made clear that you are not interested in that. I also know from your previous email that you do not trust this medium. I am not going to try to persuade you here but feel the need to comment on this for the benefit of others that will read this thread. Oil modified alkyd resins have been in use since the 1920s and have stood the test of time. They remain more flexible over time than oil paints and paints that incorporate them are less soluble to the action of organic solvents than a paint that contains only a drying oil in the same proportions. This is a separate issue than if one does not like the feel or rheology of paints containing alkyd medium. Honestly, I never liked the feel of oil paint with an added gelled medium. I have less of a tactile objection to fluid alkyd mediums.  

    Anyway, alkyds are out for you. I wonder if you could substitute a faster drying bodied oil (homemade sun thickened oil comes to mind) for the very slow drying stand oil.

    If you really do like the stand oil/turp mixture and only object to the dry time, I wonder if it would not be a good idea to just add to your medium a few drops of cobalt drier, or even better a system drier (a mixture of metal salts known to accelerate the oxidation of oil films).

     I generally do not recommend that artists add driers to their paints and mediums because it is way too easy to add more than necessary and risk compromising your paint film over time. If you performed systematic tests and only added just the amount necessary to make a glaze layer that dried in a reasonable amount of time (a couple of days) this should be safe. If it were me, I would make up a batch (eg 8 oz) of your dilute stand oil medium and add a few drops of drier. Then add this to a blob of paint and create a typical glaze. Test how many days this takes to dry. If it is still too long, add another couple of drops and try again until you figure out the proportions necessary to create a glaze that meets your requirements. Do not add more than necessary.

    I hope that this was of some help. Feel free to post a response if I somehow missed the point of your question. Additionally, others may have suggestions that I did not think of.

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    ​To the original poster: It seems that the jury is still out regarding your specific question. What I would state is that cotton fibers in general are much shorter than flax (linen)...this can certainly contribute to potential deformation later on down the road. Speaking from personal experience I tend to see more planar deformations occur in cotton duct canvases than in linen but more research needs to be done in order confirm my observations. All in all such deformations can be readily dealt with by conservators....I would just ask that you consider using a stretcher with expandable corners or even stretching your large format canvas over a rigid support (backing boards are also good). Hope that is of some use.

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    ​We recently heard back from one of our scientists (Dr. Chris Petersen, a retired organic chemist who formerly worked at Dupont). Here is his comment:
    "There would be minimal penetration of the vapor if the paint is simply exposed overnight; clove oil is a phenolic type antioxidant with a boiling point >250 deg. Surface penetration is actually what you want if you are tyring to prevent the drying effect that is propogated by oxygen promoted free radicals. The stuff does have a strong odor so even a small amount in the air is overwhelming. As an interesting aside, phenolic antioxidants are used to stabilize acrylic monomers like methyl methacrylate so they can be shipped and stored in bottles. When you add an initiator to make a polymer, the inhibitor is consumed and the free radical reaction occurs."

    So in summary there would in fact be some penetration, albeit minimal. Dr. Petersen therefore also believes that this would not drastically impact the "health" of the paints in the immediate future. 


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    ​Also I am posting this on behalf of conservator Laura Fuster: 

    I thought the artist might find of interest the proceedings of the symposium ‘Copper painting and other metal plates: production, degradation and conservation issus’ held last January at the Polytechnical University of Valencia are available at : http://www.lalibreria.upv.es/portalEd/UpvGEStore/products/p_2102-3-1 ‘Copper painting and other metal plates: production, degradation and conservation issues’ ‘La pintura sobre cobre y otras planchas metálicas: producción, degradación y conservación’Edited by L. Fuster, I. Chulià, MF, Sarrió, ML. Vázquez, L. Carlyle, J. Wadum226 pagesFull color, 22 chapeters (18 in English, 3 in Spanish)ISBN: 978-84-1684-696-2

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    ​We have representatives from Amperstand on our industry contacts so I will send them this question to answer.

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    ​Hi -

    Using GAC 200 in this way is fine, just keep in a few things in mind:- it is only water resistant and not waterproof, and certaainly a polyurethane would produce a harder and tighter film. 

    - when using GAC 200 alone and creating a continuous film, we recommend having it dry at a min of 70F. Otherwise there is a chance of  microscopic microfissures forming that are not really visible to the naked eye. We noticed this when testing GAC 200 as a size for blocking oil. When dried at 70F or above the films were succefful at blocking oil, while below it grew increasingly able to allow small amounts of oil to penetrate through.

    - if the above is concerning, you can add some GAC 500 to give some additional flexibility and a lower film forming temperature. A 3:1 GAC 200:GAC 500 ratio would be good. You should still have a nice low tack film.

    -  if you are finding hardboard to be prone to damage have you considered using something more substantial such as MDO (Medium Density Overload)? Because it comes with a resin impregnated paper facing on face and back, there would be no need to seal the back per se.

    - finally, if wanting to really isolate the panel from moisture, take a look at this article we published on our Just Paint site on priming panels for outdoors:

    https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjHuuaG98HXAhUDQCYKHeeiA54QFggoMAA&url=http%3A%2F%2Fwww.justpaint.org%2Fpreparing-panels-for-a-life-outdoors%2F&usg=AOvVaw3utTSHP8is6Uv73hiqjrpV

    The alkyd primers used there should give a harder surface and be more moisture resistant.

    Anyway, those are at least some thoughts. And if you like what you are getting, then there is no reason to change.

    Hope that helps.



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    ​I was uneasy about the statement that most commercial artists' canvases were composed of blended fibers but refrained from commenting until I heard from someone in the industry. I received this comment today and am posting it for them. Their response is in black.

    The majority of commercially available artist canvas is not PolyCotton.   

    https://www.artcons.udel.edu/mitra/forums/question?QID=341

    Artist Canvas is available in three distinct categories:

    1) Linen - this is fabric that comes from the fibers of the Flax plant. It is very sturdy and durable. (warning - much of the canvas from Asia that is referred to as linen is a 100% cotton fabric that has been dyed to look like linen)

    2) Polyester and/or PolyCotton blends - synthetic fabrics or synthetic blends. This is especially prevalent in student grade canvas panels and works great for smaller stretched canvas.

    3) 100% Cotton - The majority of Artist Grade Canvas is 100% cotton. A great example of 100% Cotton Artist Canvas is the Fredrix Pro Dixie or the Fredrix Red Label Cotton Canvas.

    We’d be happy to send samples to your industry expert if you’d like.

    Best wishes,

    Paul Straquadine

    VP Sales Tara Materials/Fredrix Artist Canvas

    322  Industrial Park Dr

    Lawrenceville, GA 30046

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    There are a couple of comments here.

    As to the sandpaper, yes, it is important to abrade the surface to provide tooth and the solvent is used to degrease the panel.

    Ben, most copper corrosion products are in the green to bluish green color spectrum. These products range drastically in terms of reactivity, stability, and effect on the copper object. Copper chloride also known as bronze disease is at the bottom. This means that the form of corrosion that occurs between the copper and any oil ground or paint will have an effect on the stablity

    Ben, your friend’s supposition about the sulphur promoting a specific chemical reaction which may be more stable, that was precisely what I was alluding to in my initial response. My first draft mentioned sulphur containing thiol groups and the preferential creation of more stable sulphur containing copper compounds but edited that out. Perhaps this limits the degree of the greenish corrosion but on the other hand, sulphur is one of the things known to promote darkening of lead white oil paint so…there are still questions here. Again, I do not believe that garlic juice is a necessary step but its use is interesting.

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    ​Hi

    I cannot specifically state what the Old Masters for this purpose, as there is little archival documentation and organic analysis is far more complicated than was once believed. I would suggest that any additions to the paint were rather simple and not likely to contain high proportions of soft resins like mastic or the resin in larch turpentine. The reason that I say this is that fine thin lines applied over dry underlayers are the most susceptible to abrasion and yield under the actions of strong solvents and extreme pH. These were precisely the materials used by restorers in the early days. If it was common practice to add large amount of soft resin to the paint, there would be few examples of these fine lines on Old Master paintings for us to see today. The danger of this practice is obvious when examining 19th century maritime paintings where the rigging is often completely abraded away when the artist used a lot of resin to accomplish these fine lines and/or when a poor restorer cleaned the work without the knowledge and sensitivity needed to clean such works.

    I would separate the methods of the Renaissance and Baroque from those of the 18th and 19th centuries when it was almost universally accepted practice to use mediums with very large amounts of soft resins. This is an instance where mediums containing hard resins and oils yielded more stable results than did the mediums containing softer resins (BTW I not stating that resins are necessary). The less soluble hard copal and amber mediums (if amber was ever a common paint additive is a completely different debate) create a paint film that is more resilient to the actions of cleaning. The oil-fused hard resin mediums did tend to yellow strongly and become brittle if used indiscriminately. Today we do have alkyd mediums, which fulfil the same role but are less yellowing and more flexible. Whether you like the way that they feel and move is another issue. I have generally preferred the fluid alkyd mediums to those that have a gel-like consistency or an intentional thixotropic quality in emulation of megilp.  

    So as to practical application tips, I do think that some addition of a long oil like stand or sun thickened oil in a suitable amount of solvent added to the paint will help. The couch of oil will make this easier but the practice is problematic. This is the same issue as that of oiling out. Any oil film that is not covered by a layer of paint will eventually darken and become obvious. This may be minimal if the application is extremely thin, but even then it will probably become visible in the long run. You may be interested in browsing through the section on oiling out in “Resources Section” to read a bit more about this issue.

    It seems to me that after the skill of the artist, the most important factor is the choice of brush. In my experience, the best are high quality kolinsky rounds with longer brush hairs. There is a reason that there is a brush made specifically for painting the super fine lines used to depict the rigging on ships. These very long rounds are even called riggers. Now these may be too long for your needs but you get the general idea.

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    ​Thanks Brian. As for your aside - you clearly are one of those painters ready to pounce!

    Ugh - I know.   :)

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    Sarah

    Good info and call on the Incralac. That slipped my mind but makes sense in this context. You are completely right about the probable superiority of other substrates. It is true about the allure of the visible copper surface but it is also true that a very high proportion of historical oil-on- copper panels had some sort of ground. This does bring us to one of the fallacies mentioned in the "Resources Section" just because some noted master of old used a material does not ALYWAYS mean that it is still the best tool for the job. As an aside, I always pounced my lead white ground with the palm of my hand (protected by wearing a nitrile glove) very thin so that the sheen of the panel could still be discerned through the thin ground layer.

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    ​Hi -

    I only have a few things to add to Brian's comments.

    But first I would want to ask why you are choosing copper in the first place, especially if willing to prime it - thus losing any of the metallic, reflective sheen that painters like Claude Lorrain were attracted to. And beyond that is the simple fact that copper remains a reactive metal and there are definite mechanism of degradation of oil on copper that are a real concern. See The degradation of oil painted copper surfaces by Lydia-Chara Pavlopoulou and David Watkinson for a good and current summary:

    https://www.academia.edu/1031822/The_degradation_of_oil_painted_copper_surfaces

    Certainly the analysis doesn't mean that all paintings will fail - only that they are vulnerable given the potentially reactive nature of the oil/copper interface. It would see to me that if wanting something that is more stable and equally rigid and lightweight, that aluminum-composite panels - such as Dibond - might be a better option.

    That said, I have certainly done my own share of oil painting on copper - although nearly always painting directly onto the copper - so know the allure. It was also a useful way for me to 'recycle' copper etching plates that students in printmaking departments would abandon at the end of the semester. 

    As for the other points, I can share a quirky test we have done of soaking bits of copper into various oils (both linseed and safflower) to look at the ability of the oils to become infused with copper ions. Its mentioned in literature as one way to make a fast drying albeit 'green' oil. Curiously, only one of the oils turned green - and from what I recall it was the one with a higher acid value. But not sure. So it might be the same with the grounds you are using - one or more of them might have an oil more prone to react with the copper.

    And one last thought - in terms of sealing the back - you might take a look at a product called Incralac, which you can find at conservation supply houses like Talas:

    http://www.talasonline.com/search?keywords=incralac

    It was formulated to protect copper and copper-alloys from corrosion, and while used principally on sculpture and objects, we have used it successfully as a form of clear primer on copper when priming with acrylics. A bit of an off-label use but we feel fairly safe. It might be a useful product to protect the backs of your plates and perhaps even as an isolating coat between the copper and the primers you are using? That latter I don't know and you would need to test adhesion and make your own assessment.

    Hope that helps.


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    Hi. Thanks for the kind words. I will respond within the text and in red

    I've searched here on the topic, and also read the "rigid supports" document in Resources (which is a wonderful reference), but I have a few additional questions about working on copper. 

    1. I'm using relatively thick copper (14-gauge etching plates) and working fairly small (maybe 11x14" or so, down to 5x7"). Is it necessary to brace supports of this size, or would it be sufficient to put a lightweight (floating) backing board behind the plate in the frame--perhaps Gatorfoam, or a layer or two of museum board? 

    I do not think that bracing would be important or even a good idea in that case. What you propose sounds fine and is exactly what I have done in the past. It may be a good idea to put an acid free interleaf between and board that may be acidic or become acidic to prevent corrosion of the reverse of the copper panel.

    2. My process to prepare the surface of the plate: degrease with denatured alcohol, thoroughly abrade the surface with sandpaper or steel wool (with the aim of completely stripping the surface to expose fresh metal), vacuum off any copper dust, then degrease again, making sure that all dust and residue gets removed. Then allow to dry, and prime. Does that sound about right?

    That sounds good.

    3. How about where the copper is not covered by primer/paint? Like the back and sides? Can I just let that oxidize, or should I seal it with something? Renaissance Wax, maybe? 

    I do not believe that most 17th century oil on copper panels were not coated on the back. There are even a few instances where the work was done on the reverse of an etched intaglio plate. However, if you wanted to avoid corrosion on the back you could spray it with an epoxy coating after degreasing the reverse. Do this before treating the front so that your degreasing and abrasion of the front would remove any accidental overspray that may have gotten onto the face of the panel.

    4. I assume any oil-based primer will work? How about an alkyd primer, like Winsor & Newton's Oil Primer? I have a few small test sheets on which I tested some straight lead carbonate in linseed oil (RGH), a lead painting primer that contains some titanium white and driers (Rublev), and the Winsor & Newton primer. All three dried very quickly (the W&N primer was touch dry in a matter of hours). I'm guessing that the copper is a drying catalyst? The Rublev primer turned very green upon drying; I don't think that it was a matter of surface prep, because the RGH lead primer is right next to it on the same sheet of copper, and it didn't change color at all. The Winsor & Newton primer took on a slight green tint, but it's barely noticeable. Is this sort of thing common? Something to worry about? I don't think I'd use the Rublev primer, since the color change in that case was considerable. 

    For me, priming copper panels has had a bit of voodoo to it. I have primed a group of them at the same time and using the same prep and materials and had one of the bunch turn green as well. These should be cleaned of their ground and the process repeated as such immediate corrosion is a sign of trouble, which would likely only continue if left in place. Copper can catalyze drying oils but I am also guessing that the primers contain enough driers to create a rapidly setting ground. I am unsure why the primers all preformed so differently. Perhaps they employed oils of very different acid numbers. It makes sense that an oil ground would be formulated with an oil of a higher acid number as this tends to make a paint that contains a greater percentage of pigment but one that yellows a bit more strongly. The leaness would be useful in a ground and the yellowing would be far less of an issue than in a paint used for surface effect. Again, all of this is conjecture.

    If you have the time, it would be useful to make a test of the available grounds and let them really oxidize for a while and then test for scratching before deciding on your preferred ground. I have always used lead white in linseed oil without a drier. There may be better modern materials for this but I have not personally tested them. I know that there has been a good bit of experimentation with various coatings on aluminum panels. I will send this along to a couple of our other moderators to see if they have anything to add.

    5. I skipped the oft-recommended garlic step, just on the basis that I have been able to find a consistent or empirically supported reason for its use. Some sources say that it helps to "etch" the metal (though it is unclear how, since garlic is not acidic). Some sources say that it might serve as a wetting agent (which makes more sense, except for the fact that copper doesn't seem to need a wetting agent--it takes oil paint really well, with no beading). Some sources say that it helps the paint bind to the surface chemically, rather than just mechanically, but I don't think that's correct. Don't oil films exchange ions with copper? In any event, the idea of putting an aqueous paste between the metal and primer seems like a bad one to me, but perhaps there is a purpose for this step that I haven't considered?

    I do not think that garlic is necessary for a stable panel. Garlic is not very acidic but a cursory internet search shows that it has a pH of around 5.8, which is well below neutral (7). However, I do not believe that etching plays a major role here no matter what. The dried garlic juice does create a slightly pebbled or textured surface that may promote adhesion.

     As to whetting, I have personally seen thinned lead white ground bead on a copper panel that did not have such a layer. This may have just been an isolated occurrence or perhaps that panel was not sufficiently abraded.

    I have discussed this idea with a fellow conservator who is more science savvy and they suggested that the garlic may also perform an additional effect; promoting a more stable form of corrosion. The copper is going to corrode to some degree at the interface between the panel and the oil primer (perhaps there are modern materials that would not do this) All cross-sections of paint taken from oil on copper paintings that I have seen exhibit a green layer at the bottom of the oil priming. The sulfur in the thiol groups contained in garlic may promote the creation of more stable corrosion products.

    In closing, though, I do not believe that the garlic application is necessary nor does it absolutely make a more stable panel, I do believe that people did believe that it did, and that this was because of some of the aforementioned reasons.

    Thanks!

     

    -Ben

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    I will assume that you are talking about the use of isolation varnishes between layers of oil paint. Isolation varnishes between disparate paint systems are a different idea and may or may not be advisable (eg applying a coating over a very absorbent aqueous paint system to cut the absorbency before applying oil glazes) Also, the concept is different with some other mediums. I can see no really issue with using clear interlayers of acrylic dispersion mediums between layers of acrylic paint. Acrylic dispersion are an excellent adhesive, where drying oils really are not.

    This use of isolation varnishes in oil painting should be discouraged for a number of reasons. First, it is generally a bad idea to reduce the mechanical tooth of a paint layer, which could promote delamination or flaking of the superimposed layer.

    Second, adding the varnish layer between paint layers will introduce an unnecessary solubility issue. Even if it is covered by additional oil layers, the varnish could be attacked and undercut during a restoration campaign resulting in the loss of all subsequent layers. For instance, a layer of natural resin between paint layers will create a paint stratigraphy that is sensitive to hydrocarbon solvents, even those containing a low proportion of aromatics. A layer of shellac between oil paint layers introduces a sensitivity to alcohols, etc.

    Additionally, the use of varnish interlayers creates a more complicated paint stratigraphy. We know from examination of historical paintings that the more complicated the stratigraphy, the more likely there will be some failure in the future. This does not mean that one has to create paintings in only a few layers, but you should aim to use as few layers as is necessary to create the desired effect.

    The varnish interlayer will also respond in a different manner to movement of the substrate than will the paint layers below and above it. It will also age differently. The flexibility of the varnish may change drastically over time making it less flexible than the layers that it is covering. Etc, etc. So, for the above reasons, and likely many that I am not thinking of at the moment, it is really best to avoid the use of isolating varnishes in oil painting.  

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    Most commercial cotton canvas offered today are actually blends of cotton and polyester fibers. Some cotton canvas we have studied consisted of as much as 65% polyester in both the warp and fill weaves.

    It is generally recommended to use 320 g (~10 oz) unprimed linen canvas and 320 to 400 g (10 to 12 oz) cotton canvas for pictures larger than 120 cm (48 inches). Cotton and polyester canvas has strength closer to that of linen.

    Light-weight: 140 to 170 g (4 to 5 oz)

    Medium-weight: 240 to 270 g (7 to 8 oz)

    Heavy-weight: 320 to 400 g (10 to 12 oz)

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    Watercolor owes its impact to the to the miraculous ability that water has to move pigment and other colorants, into fresh and lively patterns. Adding any surface coating, wax, varnish, or a synthetic dispersion, diminishes that impact, by adding a layer, through which one has to look to see the paint. These coatings are permanent and each has issues associated with it: wax may discolor, attract dust, and change the hue of the watercolor, varnish is likely to discolor and to change the hue of the watercolor, as will  synthetic dispersions. If the use of sheet glazing is too problematic, artists can paint in acrylic paint, encaustic, or other media on watercolor paper, but the paper can not be left exposed and the medium will have to stand up to traffic, oxidation, and other pollutants. Well sealed framing, with reflection canceling sheet glazing protects watercolor, and friable media from traffic, pollutants, including oxidants, and is well worth the investment.
    Hugh Phibbs

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    Hello!  Sarah's answer is great, and about as thorough as you can get, so I can only add a couple of things from a conservator's point of view.  From a paper conservator's perspective (or at least my perspective, others may of course have a different view), not enough testing has been done yet on how these newer varnishes age or degrade over the long-term to be able to predict how they might change a watercolor painting in the future, both aesthetically and physically.

    I can say that varnishes can be exceptionally difficult to remove from paper, particularly as they age, and would also affect how cleaning is carried out.  My instinct is to suggest, as Sarah said, that you experiment to see if you like the results of using a varnish; but I tend to think that mounting under glazing is probably the safest way to protect and display watercolors on paper.

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    ​Hi -

    You are correct that displaying watercolors without glass by varnishing or topcoating them in some way has gained a lot of popularity in the last few years, and while I cannot address many of the conservation issues, I would like to share the testing we have done on the degree of UV protection you get with UV filtering varnishes, vs museum grade UV Plexi, vs no UV protective coating. You can find that testing summarized here:

    GOLDEN Archival MSA Varnish Over Transparent Watercolor on Paper


    You will also find a really clear example of the amount of protection varnishing can provide if you scroll down to the image of Alizarin Crimson used 

    Alizarin Crimson: Now You See It…..


    That said, one can also not avoid the aesthetic impact that any coating of a watercolor will cause as understanding that is critical:


    Aesthetics of Varnishing Transparent Watercolor


    Summarizing some of the above, we would say that for substantial UV protection you would need to use a minimum of 6 sprayed coats of a UV Varnish but that will inevitably lead to a sense of the piece being laminated or at least clearly coated with a layer, that dramatically changes the aesthetic of the piece - invariably saturating and shifting the color and changing the sense of the surface and how light interacts with it. A far better option, if wanting to hold onto those aspects, would be mounting it behind non-reflective UV Museum Plexi. Expensive? yes - but really there is nothing else like it, and the best of them (such as the products put out by Tru View) can be nearly undetectable with no glare.

    Addition issues to think of - once a varnish is applied directly to an absorbent delicate surface like a watercolor it is essentially unremovable and should be considered a permanent addition. The watercolor and the varnish or topcoat are inexorably linked and whatever happens to those topmost layers might not be reversible. Thus it becomes critical to chose something that will not yellow and one is still needing to handle, ship, store and mount these works with great care, treating them as delicate surfaces in their own right.

    Not being a conservator I cannot speak to the issues of cleaning, or the difficulties of repair.

    I would close by saying that of course artists will explore and push boundaries and there might be things that this approach offers that is not achievable in any other way - such as the ability to work larger or on things like canvas. But if interested in exploring this direction, do a lot of testing to really familiarize yourself with how these look aesthetically, and be willing to accept that in many ways your piece would no longer be a watercolor in the way that is normally understood. That is neither good or bad - just somethng to be accepted. It might very well open up new avenues of expression that are exciting to explore.

    Hope that helps!


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    ​Hi

    That is outside of my area of knowledge, perhaps others on the forum can be of help.

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    I can see no advantage to using anything other than linseed oil in a true oil ground (alkyd grounds are a different issue). The flexibility and stability is more important than yellowing in a ground. Additionally, grounds should be leaner than oil paint meaning that the yellowing should not be a major factor here.

    Not all rigid supports respond the same. Different species of wood respond differently. Different cuts of wood respond very differently. Plywood responds different from wooden panels. Metal panels do not expand and contract with changes in humidity but will to some degree with changes in heat, according to their thermal coefficient. Panels with fabric applied over the panel…….etc, etc, etc. In GENERAL they move less than fabric but again, see above)

    Heat and light will always increase chemical reactions, including oxidation. A minor addition of heat like you mention would probably not cause major problems (although I do very, very slightly worry about causing the outside of the paint to skin early making it more likely to wrinkle or even crack). Higher temps, etc should be avoided as they may prematurely age the film as well as the concern above.

    It is best to not add driers, especially indiscriminately like is usually done when a artists is adding driers to small amounts of paint, where it is difficult to get good rations (as compared with when it is done by a manufacturer where they have the real ability to measure out small percentages (eg .05%)  

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    Hi

    There are a number of factors that contribute to proper adhesion of the oil paint layer to the ground (which I believe is your question; correct me if you mean the adhesion of the primer to the support). The degree of tooth (mechanical) plays a major, and probably the central role in good adhesion. Oil paint will adhere to either type of ground if they are properly formulated and applied. On rigid panels where movement and flexibility are somewhat less of an issue as compared to canvas supports, I would think the choice would be aesthetic rather than structural.

    The fingernail test is one that shows when it is possible to apply paint, not necessarily when it is optimal. I default to the older maxim that it is best to wait 6 months before painting on an oil ground. Alkyd and faster drying grounds would be optimally ready far quicker. We really need more conclusive testing (if this has been performed, I am unaware of it) before I am willing to say that there is no benefit to waiting for oil grounds to cure.

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    ​Hi

    We have recruited a textile conservator to comment on this question. Please check back in a day or so. Thanks

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    Sarah, that sounds very promising. I'm glad you shared your results.​

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    I suppose it depends on what one expects to extract from the resource, and how to apply the information. If you really think you're going to find the verified secrets of the Old Masters, those old books are going to break your heart. It has to be acknowledged that Moreau-Vauthier's reverse-engineering of Roman encaustics is just not useful to a painter today. Then again, he happened to study under Jean-Léon Gérôme, and he wrote books on how to paint- that's worth a look. Read The Painter In Oil by Daniel Burleigh Parkhurst and see if it doesn't make you want to step up your game. The best of the old books have at least one valuable lesson to teach: there are some things a painter must be able to do very well, each time, according to a professional standard. That lesson was attractive to many in my generation, who were taught by old AbEx adherents at a time when traditional skill was too often derided. 

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    Matthew is correct about the writing about craft, modern ingredients, long-term performance, and safety. As to painting practice, the answer is very complicated. The Carlyle book is rather unique, but its purpose it to document the manuals of the 19th century British writers on the subject and the materials produced at that time. It is accurate about that, but it documents a period in time when writers were the most misguided about painting practice. I would not use the included recipes as models of good painting practice.   In many ways, these are the types of books that remain relevant for the longest period of time as they do not rely on the interpretation of incomplete data.

    As to more recent writers on the craft of oil painting, there is a famous book of painting formulas that contains many, many recipes that should NEVER be added to oil paint. Maroger was just completely wrong about just about everything he included in his infamous book. Mayer was very good in spirit, although today his recipes for glazing mediums containing 50-50 oil-damar are considered very problematic. Some of his tenants are timeless while other suggestions in his tome are obsolete today. I can think of no inaccuracies in Gottsegen, and his book is very useful if a bit conservative. The situation today is far more simple about pigments, as long as you have the actual pigment number it should be easy to find information about permanence. Painting practice is more complicated. If it were not, there would be little use for a forum like this one.

    Some older books are generally on the mark even though they have some of the particulars wrong. Most of the descriptions that attempt to outline the methods and materials of the Old Masters, however, were completely off base. Doerner was so off that much of what he suggested created paintings that are already in very bad condition. A. P. Laurie and Church are less problematic and some of the 19th century volumes are better since they focus on interpreting old manuscripts, although, even in this, we need to be very careful. Few of these are authoritative. Even Thompson's Cennini translation has been shown to contain over 400 mistakes, some of these are quite crucial. There are new and authoritative translations of both Cennini and the Strasbourg Manuscript. The translations of De Mayern included in Fels's book is also problematic as it is an English translation of a less than perfect German translation of the original manuscript.

    We do live in a golden age of publications on historical painting practice. Most current monographs on Old Master painters contain a technical section that can provide real information. However, to be absolutely honest, even the early issues of the National Gallery Technical Bulletin should not be read as gospel about historical painting practice as they based some of their assumptions on analytical instrumentation and data that is now known to be insufficient to make definitive conclusions. The most obvious example is their initial pronouncements that tempera grassa was a very common medium in 15th C. Italy based on their early chemical analysis. We know know this analysis is more complicated than they initially thought and most authorities on the evolution of painting in Italy no longer accept that supposition. For the most part, though, TNGTB is a wealth of concrete information about documented historical painting practice. Publications by conservation scientists and conservators working together, published in the last decade or two can generally be relied on….as far as we know today.

    This is probably a less than satisfactory response but it is an accurate description of the situation as it is.

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    This is a pretty broad question. Where manufactured art materials are concerned, the most current information about ingredients, long-term performance and safety are obviously better than old data, so out-of-print books are progressively less useful in this regard. As research materials for learning the craft of painting, however, older handbooks can be really valuable. Craftsmanship is about learning standards of performance, how to define them for oneself and how to meet those standards. In my opinion, a book like The Technique of Painting by Moreau-Vauthier, for instance, still has a lot to offer the skilled trade of painting, even if many of the materials covered are now obsolete. 

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    ​Just wanted to share that we have applied oil paint to this paper - both straight and thinned with some solvent - and examined a cross section under a microscope and the paint did, indeed, appear isolated from the fibers. But the testing was limited so all the usual caveats apply.


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    ​If you are ok with using acrylic then I might suggest going that route simply because oil paint on paper will almost certainly cause some degree of yellowing in the future....this is not a big deal however if you are covering the entire surface with paint but based on your description thus far it sounds like some of the paper substrate is visible so staining might be an issue for you down the road (or maybe not). As for fixatives you might be interested to read the thread here on our opinion regarding commercially available products but yes, you most certainly should spray and not apply by brush.

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    ​The manufacturer explanation I have seen is that, since the paper is internally sized (in the wet pulp), the cotton fibers are isolated. It was explained that the sizing itself allows solvent and vehicle to penetrate the paper surface, but the paper fibers are apparently not in direct contact with the paint vehicle. The actual sizing was not disclosed, which naturally made me start guessing. My current stab in the dark guess is a synthetic like AKD, though I have no data to back that up.

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    ​I am sorry to say that I have not been able to find out what is in this product, much as I have tried. This has come up when I was in France and I had to admit ignorance. Since there is protein sizing in their watercolor paper, they could simply size the surface more heavily, and keep it simple, but that could lead to discoloration, if the paper is left exposed and is on display. Their description mentions it being cotton, with CaCO3 and no optical brighteners, and they also mention its absorbency (which is mentioned in the artists who tout it on line) and I keep asking myself how can the fibers be protected from the fatty acids in the oil, if the paper is absorbent? Crescent makes a paper that resists media going through it, which I think has a wax core, since it can be torn, but I don’t think they recommend that for oil. I have worked in oil on Arches Watercolor paper and it does come through, so there is something more added, here. What I have done is to begin working in acrylic washes and building up to thicker layers and then oil and those look good decades later.I  will continue to look. If this paper were adhered to a panel, like Dibond, with acrylic medium, I think that combination would be durable. 
    Hugh Phibbs

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    I am first very surprised that any conservation professor would ask for such specifics due to the vagueness of the original recipe. I have tried to reconstruct Cennini a number of times and it is very difficult to get satisfactory results. Many years ago I asked a similar question on the site that this forum is inspired, AMIEN and I was unable to find anyone who could give me the info that you seek.

    Kremer Pigments has this down but I have asked a couple of times and they are reluctant to give it out their procedure. There are many variables and the short answer is that I have not worked out a system but have achieved satisfactory result using a simplified version.

    First, you need to select the purest and deepest pieces of lapis. Remove any obvious impurities first, then crush and again remove any impurities. You can heat the stone to a high temp and quench in water where it will break into much smaller pieces. I tried this but ended up pounding and crushing in a mortar and pestle. Then grind the powder to a mid-coarse powder (something like 50 micron or so). You will need a series of sifting screens. It is still an enormous amount of work to hand grind the powder to even this moderate degree of fineness. Access to a mill would make this so much easier. I have then melted together something like 1 part beeswax, 3 parts rosin, and 2 parts mastic resin. This mixture is the 1 part by volume. To this I added about an equal volumetric amount of powdered lapis and heated and stirred all together. I did not add any oil like suggested. This was then poured out onto a piece of mylar. My previous attempts at this process ended up saponifying the oil in the alkaline water solution and complicated the process. Probably my pH was too high.

    I made balls of this after it cooled. I then let them age for a couple of weeks. I them put them in little scraps of artist’s linen. I made up a number of basins of water (maybe a quart apiece) to which I added a tablespoon or so of potassium carbonate (the lye of Cenneni’s time as opposed to caustic lye which is sodium or potassium hydroxide). I did not add oil to my hands but used nitrile gloves other than that I followed the remaining extraction process mention in Cennini.

    My result were visibly purer ultramarine but the yield was rather low and the extraction process took a very length period of time.

    In the long run, I am not sure that anything that I provided here will be of any help. I had many frustrating attempts to carefully follow the recipe in the distant past but my failures dissuaded me from taking precise notes even though I would appreciate having them today. My attempts also uses some modern materials like mylar and omits others like the use of oil. This is the best that I can do.

    Just so you know, there are later recipes for the extraction of ultramarine. You can probably references that contain them by doing a search on Art and Archeological Technical Abstracts. Some are clearly influenced by the Cennini recipe but others are a different take on the process. I am sorry that I could not be of more help.

    Please let us know if you do find a modern recipe that adds precise measurements and pH to the Cennini recipe.

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    Karri

    I am so, so sorry about how long it has taken me to get back to you.

    Your question is far more complicated than would initially seem possible. If you were able to view the talk that I co-presented the Smithsonian American Art Museum and you read the chater you must realize that paint and media are a huge question when it comes to Tanner. By the end of the 19th century, he was a highly skilled practitioner of standard oil paint media. Archival records and analytical evidence indicates that starting at least as early as 1918, Tanner began experimenting with mixed media effects, combining idiosyncratic emulsions made from a combination of mastic varnish, the mucilage extracted from soaking flax seeds, parchment glue, and a touch of drying oil and lanolin, with more common oil paints. That is one of the recorded recipes but there were probably other incarnations. There are even some notes made by Tanner to suggest that some of his recipes needed to be applied while the media was hot. This would make sense if the paints contained large percentages of animal glue. Our substantial examination and analysis indicated that he would often interlayer pigmented layers of these media with oil paints, sometimes with an intervening application of a coat of animal glue or sometimes just coat the oil paint layer with an unpigmented application of his emulsion recipe. Each of these possible layers would have a massive impact on the rheology, handling, and optical properties of the subsequent layer and the full effect achieved when viewing into the numerous paint layers.

    That brings us to another point; cross-sections that we took from Tanner paintings from around 1900 to near the end of his life all have an inordinate number of layers. Sometimes as many as 23. This number of layers and possible complex binding media make it almost impossible to really give simple directions about how to emulate his effects.

    As I wrote, it would be a good idea to read through our technical chapter, but it will not really provide a guide for copying Tanner.

    One should realize though, Tanner’s very idiosyncratic media usage did come with a price. Many, many of his paintings from his mature years, especially those with the most intriguing surface qualities, suffer from major preservation issues. This is not surprising. The more complicated the paint stratigraphy, at least in oil painting, the more likely the probability for problems. This is massively compounded when interlayering essentially incompatible materials. Finally, many of the ingredients in Tanners emulsions will remain eternally soluble in common solvents/cleaning systems. Some of Tanners paintings are sensitive to water, mineral spirits, and alcohols, making it very difficult (but not impossible for a highly trained conservator} to come up with a cleaning protocol.

    So… I worry that I have not really given you any useful advice here. Perhaps this impotence subconsciously aided in my procrastination in replying. What can I say….

    In your shoes, I would start by making experiments interlayering handmade oil paint with commercially available egg-oil emulsions to get a sense of the effects that occur when emulsions and oil media are interlayered. Then play around with adding layers of animal glue over oil layers and then add layers of tempera. From there I would expand to other hand-made emulsions. Sounds complicated, doesn’t it. The result will also probably be rather unstable as well.

    On the other hand, you could begin to explore the very different qualities that can be achieved by adding small amounts of amendments or mediums to paints that contain few or no stabilizers. These oil paints can be made by hand or purchased from a few suppliers that specialize in oil paints with no additives (when you begin working with paints like these you will quickly realize why most manufactures add small amounts of stabilizers to make the paint more useful and consistent). I do not generally laude the superiority of hand made paint as it is generally inferior to high quality commercially available paint. The issue here is that most commercially made paints have stabilizers added to avoid some of the problematic handling properties that you may want to utilize or manipulate. To a simple oil/pigment paint I would then experiment with adding oils of different handling properties (stand sun thickened, oxidized, etc) dry amendments like bentonite, calcite in oil, etc) and see what effect you can achieve, especially in layers. Really, the list goes on and on.

    As to you question about dryer paint. That is easy, make or use a paint that has less oil, or one that contain additives that make what is called a shorter paint. I am not sure that this will achieve the Tanner effect, though. You probably want a paint that is not necessarily dry but very sticky so that the color skips along the tops of the canvas threads without retaining the texture of the brush hairs. I may try adding a sticky oil, but one that does not overly level the stroke, to my paint. Something like sun thickened or oxidized oil. There are so many variable to this though that you will have to do a bunch of experiments with your specific paints to really figure out how to achieve what you want.

    So again, I apologize for the late response but I really find this a difficult question to answer satisfactorily.

    Please feel free to post addional comments or questions on this subject. It is also of great interest to me.

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    As long as the paint is not excessively diluted and the colors carry the highest lightfastness rating, I don't see a problem with the approach you describe. Less lightfast pigments like Alizarin Crimson ​can be subject to fading from UV light exposure when applied very thinly over a white ground. In terms of the overall pictorial effect, the finished work might look generally a little dark if you don't leave some pristine white passages, so it might be to your advantage to establish the strongest value contrasts early and "key" the painting to that relationship.

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    Yes, but if it's a large piece, you might want to use a large-capacity machine at the laundromat so you don't damage your home washer. If washed, the fabric should be line dried. While we don't consider it an essential step with our products, we know some artists who routinely launder canvas to remove sizings from the loom. Artists also occasionally wash canvas to remove a failed or imperfect rabbit skin glue application. Of course, synthetic-sized or primed canvas should never be put in the washing machine.​

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    Andrew Wyeth was not especially a stickler for techniques.  He liked to talk about his “wild ways” of using tempera—mixing up a bowl of tempera paint and “throwing it at the sky” and waiting to see what it looked like in the morning after it dried.  He said he did this on Brown Swiss and part of the sky of Snow Hill.  We talked often about what he did for specific paintings, so I am not able to say “he always did this” or “always used that.”

     

    His father N. C. Wyeth and his father’s teacher Howard Pyle, were both careful craftsman with an eye on longevity and “best practices” [but they worked largely in oil.]  NC was very firm about telling his four artist children to “wait a year before varnishing” for example.

     

    However, AW’s mentor and teacher in tempera was Peter Hurd who often did many unexpected mixed media things—combining tempera and exposed (highly water-soluble) gesso; Hurd may have mixed tempera and oil on the same painting.  AW told me he and Peter Hurd laughed about combining [possibly too much] ultramarine blue with Permalba to make gesso that would already be blue for the sky area.  And then at a gallery exhibition “it all fell off” – they thought this was wonderfully funny.

     

    Because critics often talked about Andrew Wyeth as if he were an every-blade-of-grass intensively focused, humorless Pre-Raphaelite, he bristled under this idea and was pleased to do surprising untraditional things.  He included an actual leaf in at least one watercolor [Virgin Birch] and one tempera [Thin Ice].   He told me he combined Brandywine mud with the tempera paint on a very large tempera called Goose Step.  I’ll vouch for that because it was too leanly bound with tiny mealy-crumbly areas and had loose areas almost immediately after it was put on display at the Brandywine River Museum.  Visitors were treated to seeing AW and Helga Testorf repainting problem areas on the painting in the gallery.  I had to treat it further later. [His two favorite historical figures were Lafayette and Washington.  AW was very intrigued by the story that Lafayette was buried with Brandywine mud in his coffin due to his time at the Battle of Brandywine.  Goose Step was painted soon after he told me that story – Brandywine mud was an almost “sacred” ingredient.  Another time he told me and others that he had used actual squirrel blood in a painting of a squirrel hit by a car.  Helga later told me that wasn’t true.  You could never be sure—he enjoyed pranks and fun stories that might not be accurate.  The only thing you can be certain of is that at the time he WANTED someone to think a certain thing was true.  Often “it ain’t necessarily so.”  He and son Jamie have told journalists a number of things that I know are not so.  I called him out on material things occasionally, and then he’d readily admit oh “not in this case” etc.

     

    But he was not obsessively concerned with “best practices.”  He liked trying to achieve new effects and then would ask me to fix things that went a bit awry.  He was more concerned with embedding emotion into his works and the associations he had to the subjects [and in the case of the Brandywine mud—to the actual material].  He called ultramarine blue “Peter Hurd blue” and you will see that trademark blue often in his work—wagons, etc.  Scratching into paint in both tempera and watercolors was also associated with Peter Hurd who had taught him fencing.

     

    I cannot say he did or did not ever use a casein ground.  But if he did, I think it was probably momentary.  [I know casein paint only as a furniture paint in the 19th century. and I might think it could be too shiny and repellent for a ground?  But this is certainly not my area of expertise.]

     

    Whether or not a casein ground would be a good idea for tempera paint, I would defer to Brian Baade who monitors this forum.

     

    Best wishes to you Koo—I so love your paintings!  

    Best, Joyce

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    Yes, Acrylic Pumice Medium is a factory-prepared product made with fine pumice in acrylic dispersion medium. There are other products like this, including Garnet Medium. These can be added to acrylic colors and primers without having to deal with unbound particles or crumbly paint.

    Acrylic Gesso alone is somewhat abrasive, and can wear down brushes. Garnet and pumice are both pretty rough on bristles, even in a medium. Brush wear can be minimized by using enough paint so that brushes move easily, but I would not use nice sable brushes with any aggressively textured medium

    Rottenstone, like marbledust, can affect film strength when used ​in excess, and might yield a ground that is too "thirsty". If you do experiment with these, you could perform a crude test for flexibility by painting samples of modified gesso on mylar, and flex the dry samples to determine whether cracking will be an issue. 

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    Dear Koo,

     

    Andrew Wyeth did indeed try to follow Peter Hurd’s description of the grounds used by Cennino Cennini.

    His first tempera was in the late 1930s.  In the early 1940s [after he married Betsy James in May, 1940] he cooked whiting and animal glue on Betsy’s toy stove, he told me, and apparently sometimes may have overheated it—there were bubbles which popped and caused pitting.

     

    However, since 1932, Peter Hurd had been using Weber Company’s “Renaissance panels” – prepared by the F. Weber Company with their “Permalba white” and animal glue, supposedly seven coats on the front and several coats on the back; the verso white gesso was then coated with a “red lacquer” according to the company.  [Weber would give artists a little vial of the red lacquer to coat the edges if they cut 4’ x 8’ panels down instead of ordering an exact size.]  Tailor-sized Weber panel came with a label centered on the back: “Made for Andrew Wyeth Esq. /date / by F. Weber” etc.  See attached photo of one of the N. C. Wyeth Renaissance panel labels.  Andrew, his father N. C., and Peter Hurd all used Weber panels.

     

    AW also mixed Weber Permalba white as a dry powder with egg yolk to make his white tempera paint.

     

    As soon as he could afford to use the prepared Weber Renaissance panels he did so, and stockpiled a number in his studio.

    He generally had the panels pre-coated and ordered them from sign painters, etc. after Weber Renaissance panels were no longer available.

    But he sometimes added more white—this could be his own “gesso” of Permalba mixed white pigment and animal glue or white tempera paint, when he intentionally scraped through the gesso ground.

     

    I hope this is helpful.  He had friends who may have made panels for him with other gesso formulations.  He used at least two ANCO panels, to my knowledge, which were, I believe, pre-coated, and I do not know what ANCO used.  The two I have seen have had cracking problems.

     

    Best wishes, 

    Dr. Joyce Hill Stoner

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    It's really important to maintain a flat plane where oil paint is concerned, so I wouldn't ever count on oils maintaining that degree of flexibility into antique age. A 10 year old oil painting is still pretty "young" but just speaking as a studio artist, I would probably not be too worried based on what you describe. I do think mounting to panel is a very good idea, to make the finished art easier for the collector to maintain.

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    An excerpt from the ​1942 American Artist interview with A. Wyeth was posted on the excellent Gurney's Journey blog, mentioning casein-based grounds: http://gurneyjourney.blogspot.com/2016/01/andrew-wyeths-techniques-in-1942.html

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    It's tricky to add marbledust to factory-prepared acrylic dispersion primer (gesso) because it tends to yield a weak, crumbly film when added in excess. Pumice is less absorbent (it's more like glass) and gives a good mechanical texture which facilitates good paint attachment. Acrylic pumice medium or Garnet Medium can be combined with acrylic gesso to add texture without taking up too much moisture from the primer.

    Braque is known to have added sand and other textural inclusions in his grounds, which were oil based. I don't think it's been established whether the "sand" was pumice, but pumice was present in his studio, so I think it's likely that he did use it on the pictures. Pumice is brutal on brushes, though!

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    Denatured alcohol is a good wetting agent for pigments that don't readily combine with water-based vehicles, and will not adversely affect a tempera medium. Disponil is a BASF brand range of surfactants used industrially for making house paint and glues. These are not available as consumer products. Paint manufacturers often have to combine surfactants with de-foaming agents, because they may tend to lather like detergent.

    I will defer to Golden on details of their Universal Dispersant, but I believe it already contains a defoamer, and is more ready-to-use than surfactants alone​.

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    If the PVA sizing adequately ​isolates the paper, I wouldn't worry about destructive effects of the oil vehicle on the support. It would be a good idea to keep the paint relatively thin, however, and apply impasto only in small passages, not in a continuous film, because PVA alone doesn't offer the absorbency and texture of a bona fide painting ground, which would better facilitate paint adhesion. Ideally, the paper should be mounted to panel prior to painting, but if you can safely mount the finished work without stressing the paint, that sounds like a pretty good approach to me.

    I would caution against making conclusions about the soundness of any technique based on the apparent good condition of historical works in a museum- the appearance of those paintings might well be the result of expert treatment and careful storage in a controlled environment.

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    I agree with Sarah, it's not a good idea to rely heavily on sizing to fill spaces in the weave. You might get better coverage, however, if you pumice the fabric before sizing. The openings in canvas weave hold air pockets that repel liquid- this is why a canvas tent can keep out the rain, until you touch it and break the bubbles. By pumicing, you may be able to comb out some fibers that will help bridge the openings and get better results with the sizing.

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    ​In terms of our own testing this would be than fine. You also might try simply applying a third coat of Matte Medium since - in general  -  a medium will be less porous than an Acrylic Gesso and so should block oil better. But then, we have not tested multiple brands along these lines, and certainly there are variations among different manufacturers.

    You might also want to see how tight or loose the linen is. If it is very open, and you can see a lot of light coming through spaces between the weave, what you are sensing as strike-though might simply be a function of very open textile. At that point you are relying on the size to bridge and fill in these open spaces, and that can mean needing additional layers. If this is true, then going forward you should try to find as tight a weave as possible as that will give you the strongest structure.

    Hope this helps.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    Good question and your feelings are well founded. Sanding will cut through the size on the uppermost fibers and leave them capable of absorbing ground or paint layers. This is no worry, though. It is best to apply a couple of thin layers of size and lightly sand the first, or first and second if you are applying three very thing size applications (two is generally preferable). Just make sure that you do not sand the final size application.

    This is the way in which I have always sized painting substrates. It is very difficult to remove the fuzz and errant threads that protrude from the surface of unsized fabric. The size hardens the fuzz/fibers so that they are more easily abraded and brushed away before the final application of size.

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    ​Although people do not really think of copper as expanding and contracting with changes in Temperature it actually does to a minimal degree. That being said it makes little sense to adhere it to a cellulosic material (wood, corrugated board, etc) that WOULD experience dimensional changes with environmental changes in a different manner than the copper panel. If you are absolutely set on adhering your large copper supports to a panel, we recommend using ACM. However, one still would need to deal with probems of proper adhesion…you would likely need to first rough up the back of your panel as well as the polyester coating on  ACM panel to give enough tooth. None of this takes into account the possibility of copper corrosion products that could form in between the adhesive and the reverse of the copper panel. No matter what type of adhesive you use this could be a problem.  What we would recommend is the following:
    Frame your piece in a sturdy wooden frame. You could make this yourself out of  molding made from a type of hardwood (e.g. oak). You should apply felt tape along the inside of the rabbet where the oak would be in contact with the surface of the copper. Also consider sealing the surface of the oak so as to mitigate any potential off-gasing that could occur. Then simply place an acid free backing board behind your panel that can be secured to the frame (non-vented would be best in this instance).

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    ​So others will likely weigh in on this but FIRST I would like to know whether the ink is on top of any varnish layers. If so then you would absolutely need to spray with any subsequent varnishes. If not then it cannot hurt to do a test...if you have an oil study lying around (or even an oil-primed surface) scribble away with the micro pen and then wait till it is completely dry. Then try brush varnishing with Gamvar. I have done this on one painting before and things were fine afterwards however I made up the varnish myself so it is possible one needs to be aware of the the solvent to varnish ratio here which is why you would need to test this yourself. Also if you want to avoid going through all of the above you can always spray the surface with a final coat of Gamvar. This is help avoid potentially disturbing the ink.

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    Hi Karri

    I am very happy that there is interest in Tanner's painings and techniques. I have quite a bit on my plate at the moment, but will respond over the weekend. In the meantime, if you can get access to it, I co-wrote a chapter on Tanners techniques (Pursuit of the Ideal Effect: The Materials and Techniques of Henry Ossawa Tanner) in the publication for the show Henry Ossawa Tanner: Modern Spirit. If you get a chance to read through that chapter, you will see why answering this question is more complicated than one might think. Finally, I wil be conducting a new study of Tanner's media this winter, which will inform a new paper, entitled:The Spiritual from the Material: An Exploration of Henry Ossawa Tanner's Complex Tempera Systems in his Later Visionary Paintings.

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    ​It has been a few years sinse I read all the way through that section. That modification looks really great. Go with it.

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    Yes, the panel back strainer is generally preferable except in areas in regions with very high and unrestrained humidity where there is the possibility of mold growth. The panel helps to keep the canvas in plane, searves as a buffer against rapid changes in the environment and protects the painting from impact form the back and even to a certain extent from the front. A keyable panel back stretcher is even better, but requires much more refined woodworking skills

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    That should work as long as it is secured to the stretchers in some manner and not exerting pressure on the canvas. FomeCore does become more brittle over time. This is not really an issue for backing boards but it may be best to not have it in contact with the canvas. A quality Gatorboard or the like would probably be better. I am not sure that Coroplast is the perfect choice as, if I am remembering it correctly, there is has a corrugated construction that is evident in the surface topography.

    I have even adhered hardboard to the front of a strainer (it is called a strainer if it is not keyable). This is very similar in concept to the panel-back strainers used by some early 16th-century Italian and Spanish oil painters as well as the panel back stretchers (keyable, despite the incorporated panel) used by some Pre-Raphaelites and Hudson River School Painters in the 19th century. This practice has been determined to be very beneficial.

    The size of your works would probably preclude the use of heavy materials like hardboard but a lighter weight material like Gatorboard may be a good idea.

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    ​​I would think that screws made for metal and finishing washers would work just like it does for wooden stretchers. As for placing foamcore inside the stretcher bars and then covering with additional canvas...I am not really sure I see the need for the additional canvas except if you want to provide some sort of buffering layer for a vented backing board. The padded backing board should be fine in this instance. You could also do something called a "cami-lining" but that might be overkill at this stage depending on the materials and technique you use but it is certainly an option. See the attached photo from the same chapter cited above.CamiLining.png

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    ​There is nothing wrong with the first scenario that you have proposed so long as the wooden support is of decent quality (and therefore is not prone to splitting/cracking and/or lots of movement...). 
    As for the second....this is a very good question and we are happy to have this recorded on the forum. I am including a screenshot of an excerpt from The Conservation of Easel Paintings (ed. by Joyce Hill Stoner and Rebecca Rushfield) from an excellent chapter written by conservators Carolyn Tomkiewicz, Mikkel Scharff, and Rustin Levenson. We would not advise using something like construction foam for the very reasons that you have already cited. But certainly something like polyester batting can be easily obtained and is very lightweight. These images will also help to give you an idea as to how conservators construct padded backing boards. Let us know if you have additional questions.PaddedBackingBoards copy.jpg

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    It would certainly be worthwhile to try BEVA 371 film on scraps of your sized paper, but I do worry about the adhesive soaking through the paper changing the refractive index and slightly darkening the paper if that size is not strong or coherent enough. The film can do this with unsized, fine canvases. Only try these experiments on disposable scraps.

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    ​Hi _ 

    We (Golden) have done a lot of testing of our products onto Dibond and for interior works feel confident in the adhesion of our acrylic Gesso to the scuffed surface of Dibond's panels, which normally have a white polyester coating that should prove to be quite stable. As for you concerns with bonding primers, there are always risks when using commercial materials but keep in mind that Dibond itself - and for that matter any metal substarate - is de facto a commercial product. Commercial in and of itself is not a death knell and I think it is a misconception that all art material companies do extensive testing of products to assure longevity. The best of them hopefully do, and we certainly devote a huge amount of resources in that direction, but in general I would wager that high quality commercial products probably are tested more and more strenuously - and based on a host of ASTM Standards - than most artist coatings. I say all of this just to challenge the conception that artists materials are always superior.  The best of them can be - and certainly the best companies will take pains to create the materials from well-understood components with an eye to longevity and durability.  And certainly when formulating an art material you are thinking of a product's service life in terms of centuries while a commercial coating might be measured more in terms of decades. I just think it gets complicated and one can never make a blanket judgement of 'art materisls good' and 'commercial materials bad'. And when dealing with various commercial and architectural surfaces - like cement, brick, metal, etc - commercial products will often be much more specifically engineered and optimized for that material. Art products, on the other had - including acrylic Gesso - tend to be designed for broader, general use rather than very narrow targeted ones.

    All that said, I think for your current needs there is no reason to go that route, but just for future reference, the ones that we have tested and recommend are Sherwin Williams' DTM Bonding Primer as well as X-I-M's UMA. We tend to recommend those over acrylic gessos especially for anything outdoors, like murals, where extreme conditions are common.

    Touching on the AMIEN position about the expansion coefficient, it is true that there is some support for that but in truth the expansion and contraction of a Dibond panel is miniscule and negligible. Especially when indoors or if comapring it to wood or canvas. I would sleep well on those scores.

    Turning to adhesion and mounting, we would point you to this piece of ours on the mounting of watercolor paper to panel as really the process would be the same, just substituting in the Dibond for the hardboard:

    https://www.youtube.com/watch?v=ggB1veQmwNU&t=5s

    As in all things, when taking on a new process, we would recommend doing a test panel just to make sure you are getting the results you want, and because reversing anything - should something go wrong - would not be easy.

    On that note, have you given any thought to using BEVA film as a way to mount the pieces? It would have the advantage of being reversible. You can find information about this product at Talas or Conservation Support System, among others:

    http://www.talasonline.com/Beva-371-Film

    http://www.conservationsupportsystems.com/product/show/beva-371-film/beva-adhesives

    Kristin and Brian could probably help further with thoughts about BEVA's use for this type of application.

    Finally, "hold out" would not be an issue in this case, when working with a softer acrylic medium such as our Soft Gel, which is what we would recommend. Hold out refers to the resistance of a very thick material to flow into the nooks and crevices of a surface, but rather just staying up on top. For example, if you spread a layer of our Extra Hevy Gel on a roughened surface, there is a liklihood of air pockets and places where intimate contact between the gel and surface is not achieved. The product by itself will not flow into those areas without being pushed in. In short, that is what hold out refers to.

    Hope the above is helpful, but don't hesitate to ask questions if you have them.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    ​There is an excellent article in "Just Paint" that discusses this very issue which I will link to here. However, I am not as familiar with certain issues relating to acrylics and adesion to aluminum coated substrates....I am hoping for example that one of our other moderators will elaborate a bit more on the issue of "hold out" mentioned in the article. But have a read and let us know if you have any other questions.

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    ​We are posting this answer on behalf of Mauritshuis paintings conservator Abbie Vandivere: The Mauritshuis image on the website is colour corrected and more colour accurate than the one in the other link. Brian is right that the calibration of your screen can have a significant effect. Also, if you look at the painting at the Mauritshuis, the blue areas (especially the back of her turban) look darker than this image; this also has to do with the lighting of painting for photography vs the gallery. I'm a paintings conservator at the Mauritshuis, and am involved in a research project about 'Girl with a Pearl Earring', where we will carry out a technical examination in front of the public in February-March 2018 (more details coming soon). One aspect we are investigating is whether degradation has occurred in the blues (and other areas), and how it has affected the modelling in the turban.We hope that the information we learn from non-invasive examination methods will help us answer more questions like yours about Vermeer's materials and techniques.In the meantime, I hope you are aware of the chapter about 'The Girl' in 'Vermeer Studies' (1996). There is also an app (available for phone and tablet) called 'Second Canvas: Mauritshuis' where you can zoom into 'The Girl' to an incredible level of detail.Good luck with the reconstruction! I would love to see some photos of your work in progress. Best wishes,
    Abbie Vandivere

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    ​Hi Richard.

    We will reach out to some conservators that we know from the Mauritshuis and see if we can find out for you. Keep in mind, though, the calibration and color management of your computers screen and printer may have as much or more of an effect that the original digital scan.

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    Oh, and just to be clear and consistent. I recommend a fluid alkyd medium and NOT a gelled medium like Liquin (regular) to facilitate pourable oil paint.

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    Let us continue the inter-text response, again in red.

    Thank you Brian for combing through my questions so carefully, that was very helpful! Most especially to hear that I am not deemed as crazy for trying to dilute oil paint to the extent of pouring it. That's been a big anxiety of mine! Now that it just about finding the right ratio, I can move forward more confidently. 

    So just to clarify- you think that (winsor and newtons) dying poppy oil, and a fast drying alkyd like liquin, are both as likely to darken/yellow over time, but that the alkyd will probably make a stronger paint film - so that's why you'd probably use it instead of the drying oil? 

    Yes, those are my thoughts.

    Also do you think I should stick to using Titanium white then, if I am using large quantities and want it to have the least chance of yellowing? Do I need to be looking for one that is bound with a lighter oil than linseed and has no zinc in it? There are so many kinds out there, is it worth going for something like Holbein's quick drying white, which is supposed to be good for underlayers but maybe its ok as the main layer too? or Holbein's ceramic white? Although its supposed to be slower drying which might not be good. 

    Again, lead white is more flexible in the long-run, but for your needs, I do think that titanium white with a solvent/alkyd medium would probably be the smartest choice as a compromise between opacity, resistance to yellowing, and flexibility. Others may disagree.

    ' I would do some tests with different concentrations of added alkyd on scraps of canvas or panel to find a happy medium between paint that is not too fat which would yellow and one which is underbound.'

    This is exaclty what I am starting to do now, a controlled test that I should have done years ago..trying differnt ratios out. 

    My only concern is being able to tell when a paint film is underbound or too fat... If the results I get, in the short term seem bound- I can scratch them and the paint will not come off!... I suppose I still can not guarantee that in the long term they will stay that way? I have huge worries about them suddenly peeling off one day.. is that completely unlikely if they seem so strong now? I think I can live with darknening/yellowing but chalking off terrifies me obviously. 

    The scratch test is really what you have in a simple studio situation. I would probably determine the ratio that allowed for a stable film in the short term and then add a touch more alkyd to surmount possible delamination in the future. Again, this is relating to your single layering sytem. More complicated layering should have a little additional medium added to each subsequent layer.

    Essentially I am wondering how to proceed with selling works that I have not proved the stability of, beyond a couple of years. Can i ethically sell them, do you think? Or is that uncertainty just something that comes hand in hand with buying oil paintings (especially of an experimental nature)?. I know you're not a lawyer, but your personal opinion, as a conservation expert, would be gratefully received.

    You can only do your due diligence and use the most stable materials and techniques that allow for the fulfilment of you aesthetic aim. This is what you can do to be an ethical creator. Anything beyond that is on our shoulders ;)

    If this is keeping you up at night, you should really experiment with a similar effect but using acrylic dispersion paints modified with some of the plethora of acrylic dispersion mediums and tested additives. As I wrote before, these are more forgiving of breaches in practice than are oil paints.  I understand your comfortability with oils, but what could it hurt to experiment? You may even discover something that you are really like with in the process.

    In the absence of this, do the experiments and tests to determine the best system and record everything on your paintings.

    Also, sorry,  one other question you didnt really answer is:

     if a painting has significantly sunk in (hopefully I can stop this happening in future), is it ok to- once primarily dry, spray it with a couple of thin coats of retouching varnish and eventually a couple of thin coats of varnish. I assume if it is really sunk in it will bond with the varnish.. perhaps this is what will darken the painting significantly, if the varnish is bonding with the paint film itself? But I cant think about how else to protect the works. Normally, on top of a non sunk in painting, varnish still always carries a risk of darkening/yellowing, right? Even if it is winsor and newton and it states 'non yellowing'.

    I tend to discourage the use of varnishes early on as they are more likely to bond with the uncured paint layers. I do think that it is best to wait until the paint is cured and then apply varnish to even out sheen. The procedure you mention, however, would likely be fine as long as the varnish chosen for the process is made from a non-yellowing and readily reversible resin. Some of the modern synthetic varnish resins really remain non-yellowing or at least minimally yellowing for an extended period of time. Read more about this in our "Resources" sections on varnishes and retouch varnishes.

    Thank you again for your time! 

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    This question is essentially answered in the Myths, FAQs and Common Misconceptions document, but since you've asked: 1: Color change (darkening) due to excessive use of Canada Balsam in the medium will not be prevented by a top coat of picture varnish. I think 1 part resin to 2 parts oil sounds like an awful lot of resin, BTW. Artists going back at least to the mid-19th c have remarked about problems with bloom and darkening when CB is used as a varnish, so this isn't a recently identified issue. 2: It usually takes a trained conservation specialist to know for sure why a painting has cracked. (I'm not one, BTW.)  A panel reduces planar distortion, but there are other stresses between paint, ground and support. If using a rigid support could prevent brittle paint from cracking, we wouldn't see so many cracked paintings on panel.

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    ​Certainly using a rigid support is preferrable if you are going to use any additives that will increase the brittleness. As for exactly HOW much you can add....well that has yet to be extensively studied. No matter what please consider recording your materials (even the proportions used) on the reverse of the painting. You might be interested in reading this previous thread here and reading a bit more about some of these additives in our "Mediums and Additives for Painting" document in the Resources section.

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    Hi Koo

    I would not use any of the synthetic resins used in conservation for this purpose, even those known to be compatible with oils. The problem is that their virtue (similar solubility after aging) is their real deficit in this instance. Have you experimented with alkyd mediums for this purpose? I have not performed these tests nor read about any studies, but they would seem a logical replacement. The stability and insolubility of these resins would be greatly appreciated if they work for your technique. In lieu of this and if you really desire the handling and hardness of a resin, use dammar or perhaps even a true copal medium if you have some on hand. The copal will yellow and become more brittle but it does become less and less soluble over time.

    No matter what, and as always, please record you medium use on the back of your artwork ;)

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    What you write is perfectly logical. It will cut the absorbency of a true gesso ground while changing its characteristics and making it slightly less water soluble (also less friendly for egg tempera) . B-72 is no worse, and generally better than most of the acrylic polymers used in synthetic binders. It will remain soluble in the same solvents that it was initially soluble in. That is both its virtue and a slight deficit for other reasons like these. For most situations that you mention, it should be an admirable sizing layer.

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    ​Because copper can oxidize and corrode, we have taken to recommending that people "prime" the copper with Incralac, which is a protective coating made for copper statuary and other art objects.  You can usually find it through conservation supply stores, such as Talas or Conservation Support Systems, to name two:

    http://www.talasonline.com/search?keywords=incralac

    http://www.conservationsupportsystems.com/product/show/incralac-solvent-based/metal-coatings

    We have tested the adhesion of our own GOLDEN Heavy Body and Fluid acrylics onto Incralac and so far it has been excellent. We have not tested other brands but have no reason to suspect they would perform differently, but testing is always recommended. Even in terms of our products since our own testing is but a snapshot in time and products constantly change.

    Also,  keep in mind this is a bit of an off-label use for this product which is normally employed as a topcoat, and we also have not had very long-term experience using it as a primer. However, it should be a stable coating when used indoors, and remains the best solution we can think of if wanting to preserve the look of the copper.  But Kristin and Brian, the two conservators on MITRA, might have additional thoughts.

    Finally, and especially if you are using the Incralac at high gloss, you might also want to consider adding something like GOLDEN's GAC 200 into our paints at a 1:1 ratio on the first pass. It helps promote adhesion to non-porous surfaces and gives the acrylic a harder film. 

    Hope that helps.

    Sarah Sands
    Senior technical Specialist
    Golden Artist Colors





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    ​Thanks for adding that note Matt.  We totally agree - and believe it was a similar issue that sparked our putting out an Advisory Notice to artists concerning Pre-Primed canvasses and how to both test to see if there is likely an issue (its a really easy water-drop test) as well as ways to help adhesion, such as the wiping down of the surface that you mention. That article, and a link to the testing process, can be found here:

    http://www.justpaint.org/advisory-notice-concerning-pre-primed-canvas-supports/

    http://www.goldenpaints.com/adhesioncanvas


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    Sorry to come in late on this one. Several years ago, we became aware that some factory-prepared canvases made in Asian countries had the residue of a release compound used to prevent sticking in the ​calendaring and rolling process. This compound was reported to have caused some issues with paint adhesion. The residue was removable by wiping with water. I don't know if it's still a problem at all, but ever since, when advising artists on using an unfamiliar, generic or private label stretched canvas, I have recommended wiping down the surface before use.

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    ​​Yes unfortunately that seems to be the case. If you search for the term "zinc" in our search field you should pull up older threads on the subject. Keep in mind that there are still many unanswered questions about zinc white....there are plenty of paintings with zinc paints and/or grounds that appear to be doing fine while others are clearly suffering from delamination, cracking, etc. (problems that have bene specifically linked to zinc as revealed by many types of analysis). I will forward your inquiry to the conservation community at large just to be sure there isn't any "groundbreaking" research that I am unaware of.

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    This is a big question so I think that I will answer within the body of your question(s). My answers will be in red.

    Hello MITRA,

    I might win the prize for bringing the most problematic query to the forum. The reason being that my methods of using oil paint are unorthodox, and I don't have the most scientific of minds. But please don't be too hasty to judge my methods. I have spent years of time and money getting to the point I have, and I am approaching you now seeking a little reassurance/guidance, but also knowing that you may not be able to give it.

    Where to begin. Essentially, I dilute oil paint to the extent of being able to pour apply it (alarm bells ringing already, I know).

    This is only a problem if you are diluting the paint with a superabundance of solvent. Pourable should be fine, watercolor wash-like would not.

    I mix oil paint in different concentrations, with a combination of solvent and medium, that when poured onto a flat laid rigid support (these days a primed Aluminium Composite board), they interact and react against each other in desirable and unpredictable ways as they meet and combine- natural forms, even fractal patterns, appear within the very dilute paint. detail.jpg Once this layer is dry, after a few weeks, I paint glazes on top in a more controlled manner. 

    What I seek in pouring oils, is a contradiction really: Stable instability.

    I know the basics...that if you just dilute oil paint with solvent it can't bind properly and will chalk off.. so I've always been careful to add oil/alkyd medium of some kind. I also know the fat over lean rule. But when I am throwing it all on together in one liquid layer- I can't really apply it that rule in the same way... 

    Diluting is not the problem, it is over diluting. In addition, adding additional binder changes the whole dynamic. The aim is to create a paint that moves in the manner you require AND that contains the proper binding strength to avoid flaking, powdering, or delamination.

    Having the disparate paints flowing into each other does mitigate some of the issues encountered when layering paints with vastly different PVCs indiscriminately. The addition of the proper amount of alkyd medium to this “soup” would probably make this less of a source of concern as well.

    The first year I was making paintings like this I used just solutions made of Turpentine and Linseed Oil, but I encountered drying and yellowing problems which I since have understood… I then adapted my method and started using drying mediums instead of linseed oil.

    Most mediums will yellow if there is too much in the paint film. Yes, linseed oil yellows the most initially but all will contribute some yellowing overtime. You were probably adding more linseed oil to the mixture than was necessary to compensate for the dilution. Did you see any wrinkling?

    The main successful recipe I have used is:

    - Liquin mixed with Zest it solvent, and Oil paint.

    This would work but honestly, the gelling component in the Liquin (if it is the standard Liquin) is fighting the ability for the paint to flow. The Liquin is specifically formulated to hold the stroke where it is put. If I were attempting this, I would use a flowing alkyd solution medium (like Galkyd but there are many suitable versions of this on the market) in just the proportion to create a stable film with the desired gloss and no more.

    I think and hope I am using enough of each, for the paint to be just strong enough to cure and not peel off. It has has made many successful dry and even paintings over the last 3 years. It gives a very thin, flat surface, almost like watercolour, once dry. It has had and almost enamel surface which succesffully took glaze on top. But I do find that it has sunk in significantly since I changed primer to Thixtropic alkyd primer (which i thought would be better on Aluminium panels) but I have read that some primers make sinking in worse.  I used to use an oil primer, which I think I will return to. 

    The more absorbent the primer/ground the more you will see sinking in.

    Q: Does it matter if a painting surface is sunk in... if I don't mind the look of it being uneven? Is the worry that any varnish will bond with the paint and not be able to be removed? – does this even matter? Can I use a few thin coats of spray retouching varnish to seal it and then later a proper varnish on top? Would that top layer of varnish be able to be removed if I did that? Is there a big danger of the painting yellowing /darkening a lot like this, even if I use thin layers of spray varnish? (winsor and newton).

    The only problem with the Liquin is that it darkens over time, and actually has over quite a short period of time in recent paintings: compare detail (liquin) early 2017.jpg with detail (liquin) late 2017.jpg . I don't mind how it has changed and darkened.. but I would like to know if you think it will continue to darken more and more..

     Because of this darkening issue, but still wanting to avoid yellowing oil.. The second and most recent recipe I am trying is :

    -'Drying Poppy Oil' with Zest it solvent and the oil paint. 

    The yellowing seen with Liquin would likely occur with the poppy oil as well. I believe that you are just adding too much additional binder to your pourable paint.

    I have started experimenting with this because poppy oil is supposed to be good for pale colours… and I use a lot of white, very pale and muted colour fields. (which is another issue.. finding the best white for using large amounts..currently using Permalba Original. But thinking of trying lead white?! As if I hadn't already made like hard enough for myself!). drying poppy oil detail.jpg  I knew poppy oil itself would be far too slow drying for what I do, but thought the one with driers added to it might work? The early stages of the experiment and I have managed to achieve a dry and even surface.. glossier than the liquin ones. But I have yet to try painting glazes on top of this layer. Q: I have heard that poppy oil is more likely to crack, is this true also of drying poppy oil? In which case, would you say the surface I have now that seems smooth and slippery, will eventually crack over time?

    It is true that poppy oil creates a less satisfactory film than linseed oil. Many will debate whether this is important or a very minor issue. I would personally use a fluid alkyd paint medium diluted in a proper amount of solvent if I were attempting your technique using oil paint rather than any of the unmodified drying oils.

    The uncontrolled addition of driers with contribute to embrittlement and even yellowing. In the proper amount they can be a godsend. Again, I would use a fast drying fluid alkyd medium which already has the optimal amount of driers added by the manufacturer.

    I am certainly an advocate for lead white when used on traditional paintings, but I don’t really think that it would add that much to what you are seeking, especially as you are painting on panels. The lead white contributes flexibility and film stability but it is inherently more yellow and possesses a significantly lower covering power than titanium white both of which appear to be needed in your work. It is also important to not add too muc medium in your final glazes. Glazes are inherently more transparent and therefore, unable to mask the certain yellowing of the binder.  A proper glaze consistency is likely less fluid that you think. Some of the spreading of the glaze should be by spreading with the brush .

    So there you have it.

    I don't know of any oil painters historically to employ methods like these, I do know artists that have done this kind of thing using Acrylic or resins. I can only find one other artist online that claims to be using a similar technique in oil: 

    https://mauricesapiro.com/viscosity-series-poured-paintings/

    But other than his comparative technique, I have not found any other information to help me navigate this process. I suspect that would be because it is unadvised to be diluting and pouring oil paint in such a way for all the potential instabilities it causes..  But it is partly the instability that makes me want to paint in this way in the first place! You see the dilemma!

    I am happy with the paintings currently as they are.. in the short term, they seem stable. But I am concerned with the long term. I would obviously like to avoid Extreme yellowing and and peeling off of any paintings in the future! It is not the end of the world if they change and crack a little bit. But if it is going to be a lot, then I would feel unethical in selling the works. OR I do you think I should include a clause when selling that says I can not vouch for the archival quality of the work?

    I am aware that what I am trying to achieve would be probably be far easier and perhaps more straightforward if I used acrylics instead- (it would sure be a lot cheaper!)… but I am not quite ready to give up on the beautiful effects I can achieve using oil paint, everything I have invested in experimenting. 

    Yes, acrylic dispersion paints are easier to experiment with and be confident it producing a stable paint film. I also understand your desire to continue using oils.

    Any tips, or even educated guesses, on ways I could be doing this better - mediums that are good for making a strong but pourable paint film?! Ratios I should keep to? or other ways to keep the work stable for as long as possible... would be greatly appreciated. Thank you! sorry this has been such a long and confused essay...

    I discussed some of this above. It is really not possible to give exact ratios other than to say that the paint should not be diluted beyond a pourable consistency. I would do some tests with different concentrations of added alkyd on scraps of canvas or panel to find a happy medium between paint that is not too fat which would yellow and one which is underbound.  

    I hope this was of some help. In addition, others may have suggestions as well. Finally, feel free to ask for clarification if I missed something here.

     

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    Generally speaking efflorescence does not tend to generate a distinct odor....at least I have never heard of this occurring when it comes to materials used for easel paintings. So I do not think efflorescence is the culprit in this instance.

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    ​One last qualification to add on the issues of colored PET:

    If it is amorphous PET or PETG with mold-in-color, in other words colored in the process of being made, it is fine.

    Though amorphous PET is usually clear, crystalline PET (which is not recommended) is a mix of translucent and opaque regions – not uniformly white - depending on the formed spherulites.   But it can then be colored to create a uniform appearance. 

    So, in the end, make sure you know what type of PET it is - crystaline (PET),  amorphous (APET), or PETG.

     

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    ​Hi -

    In ASTM's Standard for Acrylic Dispersion Grounds (ASTM D 7733) three coats of a good quality acrylic ground (aka acrylic gesso) should be sufficient to block oil penetration. We happened to be the lead chair for the development of that standard and so became intimately involved in the testing and evaluation it was based on. And in fact the vast majority of good quality acrylic gessoes did meet that requirement, which should give you some comfort. That said, however, without actually testing your specific product, it is hard to know if it absolutely meets that standard. We will give some hints on how to test below.

    We would also point out that since three coats of a high quality acrylic gesso should block oil penetration on their own, a size is not 100% necessary. The acrylic grounds can really serve both functions. Where a size is absolutely critical and necessary is whenever an oil ground is being applied directly to to a canvas.

    Also, one question we would ask right off the bat is simply have you seen any strikethrough on any of the canvases you have done? If not, then you should have nothing to worry about. Some people get concerned that it will appear later on, but in truth if strike through happens it will be apparent during the drying process. So, if so far all looks good, I would rest easy. 

    That said, if you want to test this brand of canvas and have one to spare, there are two types of tests we would recommend. One, which is really a worse case scenario test, requires that the canvas be absolutely level, then apply three drops of linseed oil from a pipette or medicinal dropper and let that sit there and dry for a couple of weeks. During that time it should spread out and penetrate into the ground slightly - showing the ground in absorbent enough to provide good anchoring - but it should NOT penetrate through. On the other hand, it also should not stay put and dry as a raised bead where no penetration or spread is apparent. That is also a failure. 

    An alternative, and more of a real world test, would be to apply whatever is the thickest application you would conceivably do, using a slow-drying high oil content paint. Alizarin crimson is perfect for this (perhaps the one use of it that is beneficial!) or an organic red, like a quinacridone or napthol red, and let that dry and see if oil penetrates through. You can also try applying some of these colors with some additional medium or some solvent, to see if in a glaze or a wash anything penetrates. Again, if the back of the canvas stays nice and clean, then no worries.

    If after all of this you are still concerned, or if your tests show any failures, then yes - applying additional coats of a high quality acrylic gesso will help. And some artists will do that regardless simply because they like the convenience of a pre-stretched canvas but like also having control and knowledge of the specific ground they are painting on. Also, it can help standardize the feel of the surface regardless of the brand of pre-stretched canvas you use.

    Hope the above is helpful. And to summarize, three coats of a good quality acrylic gesso should block any oil penetration and in the testing for the ASTM Standard most good quality ones had no problems passing that requirement.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    ​Hi -

    Happy to help further. See my answers to your questions below

    Q1: Is there a risk of ethylene glycol being released from the substrate and into the paint layers due to breakdown? Or is PET stable enough to undergo practically no degradation in average indoor conditions? 

    Under normal conditions there should be no risks of ethylene glycol leaching or outgassing from the material. Polyester is extremely stable - among the most stable of plastics - and the ethylene glycol on which it is based is not in there as a free substance but rather it is bound up into the chemical structure of the molecule. While highly technical the following will give you some appreciation of the process:

    http://pslc.ws/macrog/pet.htm

    But also TOTALLY cool to learn that Nat Wyeth, Andrew Wyeth's brother, was the person who discovered how to form PET into a bottle.

    Ah.....art and science.....

    Also check out this page as well:

    http://pslc.ws/macrog/petsyn.htm

    Q2: Are there any risks connected to using PET that has been colored? Or can I assume that the pigments are bound tightly enough to the polymer matrix to not influence the paint layers?The pigments would be tightly bound in and will not influence the paint layers. You can rest easy....

    Okay? Now.....go paint!

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    ​Great question....we do not see any problem with adding 1-2 more layers of acrylic gesso to your canvases. Keep in mind that most pre-primed acrylic canvases are heatset...so a bit different than the dispersion grounds that you are familiar with. While we do not think there will be any issues with compatability there MAY (big emphasis on may) be issues with potential efflorescence of additives between these two types of acrylic gessoes....but probably not. There are moderators on our board who are better versed than we are on whether this might be a problem you should consider down the road. Also how are you planning to apply your additional gesso layers should you choose to move forward? If you apply with a brush, odds are it might not look to great (unless you are going for a striated effect). One way to counteract this is to apply multiple layers that are heavily thinned with water. However if you are looking for a very smooth surface you can apply "neat" acrylic dispersion ground using a very wide putty knife....keep stroking with the knife until you can no longer see ridges, bubbles, etc. Yet again I am sure others with far more experience using acrylics will weigh in with more useful info (or even corrections). Finally you can find instructions on how to create a backing board for your painting in our Resources section in the document entitled "Storage, Exhibition, and Handling." Let us know if you have additional questions...

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    ​Here is more information from our chemist,  Vaikunt Raghavan:

    Listed below are the salient points of different variants:

     PET

    Semi-crystalline resin.  Higher the crystallinity, higher the opacity.   Depending on crystallinity and processing, products made could be flexible (PSA tapes, magnetic tapes, food packaging) to semi-rigid (bottles) to rigid . 

    APET

    Amorphous PET.  Amorphous PET is very transparent due to the rapid cooling below Tg during processing as opposed to slow cooling of crystalline PET.

    PETG

    This is also clear and amorphous.  The backbone is built with CHDM, a much larger molecule in place of conventional ethylene glycol, thus reducing crystallinity and lowering Tm.  Used in 3D printable thermoplastics as lower Tm helps reduce thermal degradation, reduce chain scissions and enhance optical clarity.  This is a moot point for painting applications as one would not be processing the plastic at or near Tm.

    ENHANCED UV RESISTANCE

    Some plastics are inherently more UV stable than others.  Polyimides are very stable.  Fluoropolymers such as Teflon and PVDF are stable.  PET is fair.  Polycarbonate, Acetal and ABS are poor.  With UV absorbers and UV blockers added one can improve the performance and such improvement is most appreciated when PET is used in thin film solar cells considering the temperature, optical clarity and dimensional stability requirements of these cells.  Your guess is as good as mine on whether they are useful in painting substrates.

    GENERAL COMMENTS

     PROPYLENE GLYCOL

    Thermoplastics are susceptible to specific solvent attack, but propylene glycol is not harsh enough to do any harm to PET.

    ADHESION

    With respect to adhesion, there are two distinct schools of thought.  One emphasizes surface energy and the other amorphisation. 

    The surface energy school believes that flame, plasma, corona, abrading treatment etc. change the surface energy promoting adhesion in difficult to bond substrates as proved by water contact angle measurements or dyne pens.  Bad wetting leads to poor adhesion and so good wetting must lead to good adhesion (?).

    The amorphisation school believes that the surface energy effects are too small to be of any relevance to bonding, but flame, plasma and corona treatments make the semi crystalline polymers like PET more amorphous and coatings are able to intermingle and entangle with amorphous surface that have much less order than crystalline surface.

    No matter what school you believe in,  choosing amorphous PET (APET) or PETG over crystalline PET along with a bit of surface abrading and cleaning should put you in a winning spot.

    Thanks,

    Dr. Vaikunt Raghavan

    Hope that helps further.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    ​Well, first of all, just in the interest of disambiguation, PET (Polyethylene terephthalate) is the more technical name for what is commonly called polyester. And one form of it, BoPET (Biaxially-oriented polyethylene terephthalate), is better known simply as Mylar. So yes, it is a very suitable substrate for acrylic paints and is one of the plastics covered in an article Acrylics on Plastics we published in our Just Paint Newsletter:

    http://www.justpaint.org/acrylics-on-plastics/

    I can check with the author of that article, Dr. Vaikunt Raghavan, who is one of our chief chemists, about the variations you mention to see what he says. Also, keep in mind for acrylics (or really any paints) you will want to make sure the surface is thoroughly cleaned (we suggest alcohol) and adhesion is best when the surface is lightly abraded. Finally, I do not have as much experience with oils on PET but would assume that with light abrasion adhesion should likewise be good. If concerned, you could always look to a high quality commercial bonding primer made for non-porous and hard surfaces as an initial coat, but then you would lose the transparency of the support that you apparently like. 

    In terms of studies or conservation articles, nearly everything we know of would be focused on the material as being safe or stable in terms of storage or secondary support - such as polyester canvas - but do not see anything on it as an actual primary painting support itself. That said, this one entry can be helpful to realize that not all treatments or surface coatings might be safe:

    http://cool.conservation-us.org/byorg/abbey/an/an13/an13-5/an13-507.html

    Because of this, when using polyester films ourselves, we take care to use those sold by conservation supply stores, like Talas or Conservation Support Systems, that carry the uncoated, untreated varieties.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    There are a few earlier posts on here that you should read

    https://www.artcons.udel.edu/mitra/forums/question?QID=294

    Azurite is a coarse pigment so the precautions about very fine particle size are not relevant. The copper component is toxic so observe all of the other precautions.

    https://www.artcons.udel.edu/mitra/forums/question?QID=61

    Azurite is an extremely difficult pigment to use.

    It should be made up fresh in water if being used in aqueous techniques, as it will chemically change to a greener color if kept in water for extended periods.

    It is also a pigment that loses its beautiful blue color the finer it is ground (industrially ground, not mulled by the artist, mulling it into paint does not change the particle size) therefore it is generally so coarse as to be difficult to use.

    Also, the delicate blue of azurite is easily ruined by the yellowing of an oil binder. Finally, it is a copper carbonate, which can react with the fatty acids in drying oils to and convert to a more green metal salt.

    Soo, if used in oil I would suggest using a minimum of walnut oil. Yes, the walnut oil may EVENTUALLY yellow as much as linseed oil would, but this would be only over an extended period of time. Resist adding more oil to make the recalcitrant paint move more freely. If you do so you will end up with an unsightly greenish paint in a relatively short period of time.

    Mull up the paint to a barely workable paste and then dilute with a very small amount of solvent. You may find that the methods used by the early Flemish works for you. Apply it in a few layers, the lowest with large amount of white, the middle with less white, and the final with only the amount of white required to achieve the value and hue that you are hoping for.

    I hope that this was of some help.

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    ​PET seems to be about as good as a plastic can be, but it is hard to get things to stick to it. If the paint clings well, it should be suitable, for indoors, but as sculpture conservators can attest, keeping paint  stable in direct sunlight and outdoor weather is a very tall order. Recent research that has shown that organic components in oil paint react with pigments like lead carbonate to form motile inclusions, the migration of which may be driven by climate cycling. The low permeability of the PET (PETG) sheet will slow this but outdoor display is likely to accelerate it. It is also worth remembering that the pH of rain is rather low and that when water gets into paint films, as it will, and then freezes, it has an expansive power that is sufficient to exfoliate granite.

    Hugh Phibbs

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    ​We are not so sure about glycol migration...but it seems that most testing of PET in general has shown it to be a fairly stable material. As for mediums that involve heat...well encaustic and distemper might not be great mediums for this type of support. Oils and acrylics are likely alright. But again more research is needed to confirm this. No matter what you end up going with please make a note on the back which type it is (if it is not obviously labeled already). Often when paint begins to delaminate and/or flake conservators often need to use heat to set down unstable paint so it would be nice to give folks a heads up later on down the line should something unfortunate occur to your painting. Hopefully others with more knowledge about PET studies will weigh in...

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    ​There are mixed opinions about oiling out before varnishing but our opinion here is that it is not suggested. Certainly wiping away all excess oil will minimize possible problems. You can certainly apply an appropriate thin varnish to even out the sheen in the short term.

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    I am going to assume that when you write handled by oiling out that you did this while painting and not as a surface remedy. If the latter is the case, please read our section on oiling out in our resources section.

    First, I discourage the use of the term “retouch varnish” for this purpose, as it is misleading. Retouch implies that additional painting will occur over this layer. We do not recommend the use of varnish for this purpose. Please see our resources section for our reasoning.  

    There is a history of using thinned out version of the varnish that will be used a final coating as a “temporary” remedy for sinking in soon after the painting is dry to the touch. I put the temporary in quotes because, is it really temporary? Would you intend on removing it after 6 or 12 months when you are going to put on a more permanent varnish. Likely, the varnish is temporarily fixing the sinking in but will remain on the painting. In fact, we do not recommend attempting to remove such a varnish after the waiting period as you could really do damage to the youngish paint film. As always, varnish removal should be left to conservators whenever possible.

    There are brings up a number of issues to think about. Varnish applied very early will become somewhat incorporated into the paint film as it dries making the surface have sort of a combination of binders (oil and varnish). This means that this varnish could be more difficult to completely remove down the road if it yellows. Additionally the surface of the painting may be slightly more soluble in solvents than it would have been if not varnish were applied to the new film. This does mean that one should choose a stable and relatively non-yellowing varnish for this purpose. We do have to keep this in perspective, though. The surface is likely to oxidize more quickly than interior layers and this may not be a huge issue. Very thin applications of such a varnish should not cause a major problem.

    Finally, no matter what version/method of retouch varnish you are using, please record the constituents and layering on the back of your painting for future conservators.

    Others may have additional thoughts.

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    ​A critical issue in maintenance of the coating on the magnets, to prevent oxidation.  The magnets can be enclosed in pouches of Washi, or similarly strong paper and the edges of the pouch can be attached to the art with starch. You can heat bond the Washi to a spun bond  material, to ensure that the verso of the magnet pouch can stand up to traffic, while leaving enough Washi exposed at the edges to provide hinging areas. I worked this out for the Guggenheim, when I was consulting, there, but don’t know weather they ever used it. The metal in the wall must also be oxidation proof and the magnets can be released with a stack of similar magnets. 
    Hugh Phibbs

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    I can only really answer regarding adhesives on paper, as paintings on canvas are not my area of expertise. Unfortunately, I do not think there are adhesives which are both reversible and strong enough to hold a magnet to the back of the paper. I would also imagine the heaviness of the magnets would cause distortion in the paper over time. One suggestion I have would be to adhere Japanese paper tabs to the paper with wheat starch paste, and then adhere the other end of the tab to the magnet using a stronger adhesive; this way, the tabs could be removed fairly easily from the paper support or cut away from the magnet when you want to remount. I'm not sure if this would be what you are going for aesthetically, though. 


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    Hi

    I do understand about not wanting to have a magnet on the front. Additionally, while I did not mention this in my last post, there are always issues of too much weight and stress when adhering heavy materials to un stretched and even stretched flexible supports. I only wrote what I did because I am not sure that there are really any adhesives that are both strong enough to hold relatively heavy materials like either rare earth magnets or metal strips that would really truly reversible (in the sense that their presence or residue would be invisible when removed) if they can be removed. I suggested the magnetic answer even though it may cause undue weight stress if not used judiciously; it is the only way that I can imagine such an attachment without long-term residual problems. Again, this may also cause long-term structural problems if the substrate cannot handle the weight or stress.

    However, I am a lowly painting conservator who focuses on traditional paintings. Those well versed in objects conservation, mount making, and the conservation of contemporary art may have simple answers that I am not able to provide. We will shoot some of our contacts well versed in these areas an email to see if they can offer you some more useful advice.

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    The applicability of adhesives for this purpose is sort of out my area of expertise, but I do wonder if you could not just use a magnet on both the back and on the front of the work. They would hold each other in place. The hooks could be held into place by the magnet on the front. This would allow you a removable system that would not involve adding an adhesive that will likely be very difficult to completely remove without changing the feel of the canvas and/or paper as well as any possible darkening of the adhesive residue over time.

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    ​​Sarah there has not been a study focusing on the yellowing of egg tempera paints induced by dark aging to my knowledge. Here is hoping that some conservation scientist or graduate student will prove me wrong and comment. There was a study some years back using lead white bound in egg tempera as dosimeters for paintings in certain environments but that is about as close as I think it comes when we are specifically talking about dark aging: "Dosimetry of paintings: determination of the degree of chemical change in museum exposed test paintings (lead white tempera) by thermal analysis and infrared spectroscopy" by Neil S. Cohen et al.

    You might check in with Michael Skalka at the NGA as I believe they might have many, many paint draw downs filed away in dark storage. Perhaps some are egg tempera?

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    ​While there are always new developments happening keep in mind that pigment research is really driven by the much larger concerns of the commercial coatings industry, so often new offerings are focused around optimizing performance for industrial processes, or reducing costs, and only rarely open up a new color space or greatly improved lighfastness performance that would be relevant to the arts. If you want to keep your own tabs on some of this a good entry point, that is not overly technical, might be a broad trade magazine like PCI - Pigment and Coatings Industry:

    http://www.pcimag.com/topics/2627-paint-and-coating-pigments

    Of course some innovations break out into the public press, such as the recent discovery of YInMn Blue which was covered by many outlets and which we wrote a short article on

    http://www.justpaint.org/yinmn-blue/

    as well as Gamblin

    https://www.gamblincolors.com/new-blue-color-oil-paint-yinmn-blue/

    But as we both point out, it will be quite expensive and overall does not really represent a new exciting color space. At most it should provide some increased exterior durability and have a role in specialized applications where a strong reflectance of near-infra red radiation might make a difference.

    So, long story short, almost every year the major pigment and coatings manufacturers are touting and highlighting new offerings to the commercial world, including paint manufacturers like us, but that very few if any tend to pan out as being of any interest for the artist community  in the way that broad new chemistries, like the Pyrroles, Napthols, Azo Yellows, Quinacridones, or Phthalos have provided at different times in the past.

    One question in return, that always interests me - what pigment property or quality are you looking for or would interest you? What do you find lacking in what is currently offered? As sometimes there could be a niche pigment out there that could fit your need but simply is not widely used for cost or other reasons.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    ​Ah yes....we know this material well. The main thing to keep in mind is that verdigris is inherently unstable and could very easily discolor with or without a protective coating. That being said we do have examples of verdigris-containing paint in Old Master paintings that have survived fine and no one is quite sure why. In any case it is certainly best practice to applying a varnish coating that contains UV Light Stabilizers....Gamvar actually contains a UVLS already (Tinuvin 292) so this would be one type of varnish that you could use as a protective coating. 

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    ​First can you clarify what you mean exactly by "copper resinate"? There are various recipes reported in the literature and it would help us if you could state exactly which one you are using....

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    I agree, there's really no good reason to be vague about the general composition of an oil paint vehicle. If artists are curious enough about your products to ask for detailed information, it means they are very interested in using them. Having specialist craftsmen talking about your products is an advantage you can't buy or conjure up, and when it happens, it's a good idea to make yourself available! 

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    Sorry, I intended on wrting drying.

    The problematic paints were formulated with sunflower oil. You may want to write the manufacturer and ask about this.

    I am sure that some, or even a lot, of testing is performed before the products are brought to market.

    My opinion, however, is that even greater transparency about ingredients and materials would only make everything better and give those customers that care more info to guide their buying decisions. Additionally, it could help differentiate lower and higher quality of Artist's or Professional grade paints. The terms today appear to be rather nebulously used beyond pigment choice.

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    Brian, according to my experience, you're correct- each color in an assortment is individually formulated, and siccatives are applied according to the characteristics of the pigments used.

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    ​Sorry, after rereading your post, it is clear that this is what you meant. Somehow I missed that on the first pass.

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    I cannot speak to the exact oil mixtures in the Norma paints. I hope that in near future that we can have a technical contact at Schmenke to help answer questions like this.

    The paint industry does not, in general, give exact formulations, but a list of the major ingredients. This can include precise materials like (eg walnut oil) or less precise (eg mixtures of selected drying oils) while most will give the exact pigments included in their paint. They almost never give exact amounts of small additions of stabilizers, driers, etc. Modern fine art paint manufacturers likely add different amounts of driers to each pigment oil mixture (especially in their professional lines) to moderate and help to equal out the drying across the entire range, not just a single percentage for all paint.

    As far as drying oils, please refer to our section on this subject in our resources section. The only one that you mention that concerns me is sunflower oil. Yes, Sunflower oil is available with different fatty acid ratios. However, there have been some examples where professional oil paints were made with large amounts of sunflower oil and these have exhibited major long-term drying defects. Yes, these were probably made with an improper grade of sunflower oil but I can see no advantage in its use at all other than its extreme economy.

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    The Blue Wool Standard lightfastness test is a good method for the artist to conduct in-studio testing of colors. It's not up to the ASTM D 4303 standards, which are more rigorous.

    Personally, I don't see any reason why a paint maker would not disclose what specific oils are used in a given color, barring some tiny amount of a proprietary ingredient. Nevertheless, where listing of the exact vehicle is concerned, as I understand it, under ASTM D 4302, where multiple oils, resins or gums are used in multiple colors across a paint line, it is permissible to include all possible on a given label (e.g. "Alkali Refined Linseed or Expeller Pressed Safflower Oil"). Compliance with ASTM D 4302 is voluntary, however. 

    It's important to note, BTW, that ASTM D 4302 actually prescribes the minimal use of driers for slow-drying colors that would not otherwise meet the standard for acceptable drying rate.


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    Having very little information on which to base an answer, I would guess that a "combination" of oils means a more neutral-colored vehicle was selected for whites. If these are professional-grade, manufactured oil colors, I would assume driers are added in very precise, laboratory-tested proportions calculated by paint chemists. At least, that's my experience with paint manufacture. Exact formulas for oil paints are often held as proprietary secrets, though it strikes me as unusual not to disclose at least generally which oils make up the vehicle.

    Many manufacturers (Utrecht included) select oils other than linseed for pale colors and whites. The use of neutral-colored oils for whites is not experimental or exclusively modern- the practice dates back centuries in the Northern tradition and is mentioned in manuscripts including William Beurs' treatise. While arguably not the equal of linseed oil, safflower, poppy and walnut oil (all similar in ratio of linolenic to linoleic acids) are still considered proven paint vehicles suitable for permanent painting. Sunflower oil is available with different fatty acid ratios, so I wouldn't make any assumptions as to general suitability based on food-grade oils- if sunflower is being used, it may be a type that is better for painting than for eating.

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    The only added consideration to think about here is that the water you use to thin your water miscible oil paint will likely pick up your watercolor underdrawing. An ink that dries water insoluble would not have this same issue.

    .

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    ​This is a question that could take days to answer :) But that being said we will do our best to reach out to a handful of Caravaggio experts who specialize in technical art history. In the meantime I highly recommend Larry Keith's article (available for free) on the paintings at the National Gallery in London....in your instance based on the link you sent I would pay more attention to the last two entries as these are more fully painted as opposed to the first painting that Keith discusses in the article but honestly the entire article is worth reading. The second article by Pheobe Dent Weil is also pretty decent. I am also attaching a list of other books that are amazing references but some are in Italian...however the 2015 text is amazing and to my knowledge one of the most comprehensive texts to date regrading Caravaggio's materials and technique.

    "Three paintings by Caravaggio," by Larry Keith, National Gallery of Art Technical Bulletin 19, 37-51. https://www.nationalgallery.org.uk/upload/pdf/keith1998b.pdf

    "Technical Art History and Archeometry II: An Exploration of Caravaggio's Painting Techniques," by Pheobe Dent Weil, Revista Brasileira de Arqueometria, Restauração e Conservação. Vol.1, No.3, pp. 106 – 110. http://www.restaurabr.org/arc/arc03pdf/07_PhoebeDent.pdf

    Caravaggio's Painting Technique: Proceedings of the CHARISMA Workshop, edited by Marco Ciatti and Brunetto Giovanni Brunetti (Nardini Editore, 2012).

    Caravaggio: La Reurrezione di Lazzaro, edited by Dalia Radeglia (Palombi Editori, 2012).

    Caravaggio: La Cappella Contarelli, edited by Marco Cardinali and Maria Beatrice de Ruggieri (Rome: Munus – L'Erma, di Bretschneider, 2011).

    Caravaggio. Opere a Roma. Tecnica e Stile. Saggi. Works in Rome. Technique and Style, edited by Marco Cardinali, Maria Beatrice de Ruggieri, Rossella Vodret, and Giulia Silvia Ghia (Cinisello Balsamo, 2016).

    "Caravaggio's underdrawing: a "Quest for the Grail"?" by Roberto Bellucci, Cecilia Frosinini, and Luca Pezzati. In Book. Studying old master paintings: technology and practice: the National Gallery Technical Bulletin 30th anniversary conference postprints. Spring, Marika (Editor). Archetype Publications Ltd., London, United Kingdom (2011) pp. 118-124.

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    ​We do not really see any issue with this mixture. The main thing to keep in mind is to avoid creating any discernible film as this could contribute to possible problems with adhesion/delamination later on. As for thinning out water-miscible oil paints...sure...that could also be fine however realize that WM oil paints are fairly new to the world of art materials. Not enough time has transpired for us to make any definitive statements regarding durability, longevity, etc. and one brand may differ vastly from the next in terms of additives.

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    Ink underdrawings were very common in early oil techniques, especially the Flemish. These were very likely water based and were bound in either in animal glue or gum and drawn on the glue-chalk ground. The underdrawing was generally then sealed in by an oil containing, usually pigmented layer often called an imprimatura.

    Shellac-based ink is a later form of ink and it is usually called “waterproof India ink” by convention. The ink was generally made with lamp black pigment and bound in a shellac soap, created by heating the shellac flakes with an alkali, often borax. The ink is water thinnable but dries water insoluble.

    There is no real problem using such an ink as an underdrawing as long as a few considerations are kept in mind. First, make sure you know what is in the ink. Carbon black pigmented inks are probably appropriate while dye based ink are certainly not. Dye-based inks will likely fade over time and may even blead through paint layers. Also, India ink may or may not adhere well to a canvas or panel that has a rich or very smooth oil ground. However, As long as the ink does not bleed and it is not applied in an unbroken, coherent layer, this should still be an appropriate underdrawing material. Additionally, the ink should not be applied in rich puddles as this could result in slick glossy patches that may promote paint delamination. Finally, one does have to think about solubility as the work may need to cleaned or have a varnish removed in the future. These shellac-bound inks will be sensitive to ethanol and acetone, and perhaps other solvents that might be employed in a conservation treatment. If all of the underdrawing is covered by oil paint, than this is far less of an issue. However, there are more than a few paintings by my one of my favorite artists, Gustave Moreau, where it appears that he did precisely this; he left exposed ink underdrawing and even ink embellishments applied over lower paint layers.    

    Like so many other issues in materials and techniques, it is probably best practice to record your materials and working methods somewhere on the painting to guide conservators in the future.

    I hope that was of some help.

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    Given the uncertainty here, I am not sure that I could make any sensible recommendations at the moment.

    Matthew, I have not tested the effects of enzyme neutralizers on artworks.

    Honestly, unless this turns out to be a case of normal residual odors derived from quality materials, I would probably just start with afresh with new substrates etc., rather than risk the longevity of works that may turn out to be important to the OP.

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    Ammonia is commonly used in acrylic dispersion artists' paints, mediums and primers to maintain proper pH. Once in a while, (rarely) a mistake in formulation can result in a noticeable ammonia smell. If you have any leftover primer, I would try to duplicate the sequence of application. I doubt there would have been a reaction between different brands of acrylic that would cause a persistent odor but if you can duplicate the smell, it might give a clue.

    I would be interested to hear from one of the qualified Moderators as to whether an enzyme neutralizer would be safe to apply in this case, even if it's not yet determined that urine is the source of the issue.

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    In the art materials industry, the term "priming" means a transitional layer which makes a substrate receptive to paint. The primer adheres durably to the support (usually better than paint alone), hides the support material, and creates a uniform surface with optimal properties for paint adhesion.

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    A size is an application of a material used to cut and even out the absorbency of a support. This concept can also be applied to the application of a non-pigmented material used to cut the absorbency of a ground. A size should partially fill in the minute cavities of the support or ground but not be a continuous discrete layer. This could make the surface too non-absorbent and could promote delamination.

    A ground is a covering layer which generally contains some sort of filler and tends to be opaque. This should have the optimal degree of absorbency for the proposed paint medium. A ground can be smooth or textured. Generally, the smoother the ground the more absorbent it need to be to promote good adhesion.

    The definition of a primer is a little more ambiguous. The more precise use of the term is the application of an oil-containing pigmented layer to an aqueous ground layer to cut absorbency, often lock in the underdrawing, and sometimes provide a uniform color other than white. This is often called an imprimatura, although many commentators would only use that term for such a layer in Italian paintings. Despite my opinion on the matter, the words ground and primer are used interchangeably today.  Don’t get me started on the misuse of the term “gesso” ;)

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    Having not tried the Rublev ground I can't speak to its performance, but just in general, the sizing shouldn't significantly alter the absorbency of an oil ground. If the support is correctly isolated, it should not wick away so much of the primer vehicle as to alter its standard characteristics. ​Regarding which sizing approach to use: imparting stiffness is an important function of the sizing, because it helps stretched fabric maintain a flat plane, which in turn reduces stress on the ground and paint, so the addition of GAC 400 sounds like a good plan.

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    In my experience, almost all instances of cracking that I have observed in my own work as well as that of my student’s projects appear to have resulted from substrate movement, improper ground formulation, underbound paint, or too thick applications of the egg tempera paint. I have neither experienced nor read about any issues of cracking in tempera caused by titanium white.

    To be fair, as almost all of my tempera experience has been in service of reconstructing older methods as reconstructions, and I almost solely use lead white except for very short demonstrations and one-day workshops.

    I do not, however, recommend the use of lead white for artistic tempera painting. It does not offer the same benefits to the paint film in egg as it does in oil and the toxicity and expense is not justified. Tempera also does not completely coat and isolate the pigment like in oil and there is the remote chance of darkening of the lead white (really, quite remote unless you live in a very polluted environment).

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    ​Hi Koo....honestly the most common factor that is tied with cracking in egg tempera paintings is number 4. Movement (even slight movement) of the panel support will obviously lead to cracks and/or microfissures in the ground which can then migrate up through the paint layers. Unfortunately if there are already micro-cracks in the gesso ground before you paint on top you might not be able to tell until you start painting (until the surface is wet). There are certainly other possible factors of course (some of which you listed)....your comment about titanium white is interesting however. I am unaware of this issue with egg tempera and titanium white so will do a bit of digging on the conservation side of things....

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    A VERY MINIMAL amount of alkyd medium rubbed on very thin using a pad of lint-free cotton fabric. This was allowed to completely dry before working on it. It was later completely covered with paint.

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    ​This procedure and issues surrounding the practice are also mentioned here.

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    There are a couple of different components here. One of the main concern with oiling out is that any portions that are left exposed WILL yellow over time and become unsightly. We see this frequently on paintings that enter our conservation lab to be cleaned. These regions remain irretrievably darker and yellower than the sections of the surface that received subsequent layers of pigmented paint.

    The nice thing about painting into wet oil is that it becomes incorporated into the paint and is not a discrete fatty layer between more rigid layers of paint. If this layer if substantial, it will violate the general principle of keeping the more rigid layers below the less rigid layers, This would be even more problematic for canvas paintings as generally flex far more than panel paintings.

    However, one can successfully apply a minimal layer of oil/medium to cut the absorbency if one is rigorous about only adding just enough to achieve the desired effect.  I know that some knowledgably commentators state that this dried layer can be left uncovered BUT my experience in conserving paintings leads me to caution against this practice.

    Finally, I do think that your proposal to lessen the absorbency of a Clayboard panel is doable. I have done this to the same product when my project required a less absorbent ground that the untreated product. I will contact Amperstand to get their take on this as they have done a lot of R & D and testing of their products.

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    ​What you are suggesting here may certainly work...keep in mind if you are dealing with a ground that you find too absorbent you could always try to rub a bit of the alkyd medium that you are using into the surface first thereby avoiding the need to apply additional priming layers.

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    I guess one question is what is wrong with the materials you mentioned? What is the desire or need for an alternative? Knowing your motivation might help in selecting something. Is it just curiosity and novelty? Or a particular quality you are after? Also are you looking to paint on panel or canvas of some kind?

    In terms of alternatives sizing methylcellulose can indeed be used as an alternative to rabbit skin glue​ and it is something I have done a couple of times, a long time ago, but beyond that personal experiment, and the fact that it is used as a size for paper, I do not know of scientific studies about its use on canvas. And as Matte mentions, PVA is also viable - though just as synthetic as acrylic, if for some reason that is an issue.

    As for a substrates you can paint on directly, keep in mind that painting on a substrate always has the drawback that the future of the work becomes intimately bound to the future of the substrate itself. With no intervening ground what happens to the one happens to the other. That said, there is a history of painting directly on copper, and one can also paint wood with no primer, and there is also an Oil Paper made by Arches that can be painted on with no additional prep and has a nice feel.

    Hope that helps.

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    It sounds like you might be asking about sizings as well as primings. PVA sizing is available as a ready-to-use preparation. For the ground, you might try an oil-based primer thinned lightly with ​solvent-free, walnut-based alkyd medium. Also, since you mention support materials that can be used with no in-studio prep, why not consider factory-primed canvas and panels?

    By the way, in deference to Mr. Gottsegen who certainly would have pointed this out, and at the risk of sounding like a nit-picker, I want to mention that the term "archival" is often used when artists really mean "durable to the standards of permanent art". I know this doesn't help directly answer the question, but I'm pointing it out because writing here makes me miss Mark.

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    Remember, artists' oil colors are not utility coatings, they are specialist materials for a sophisticated historical craft. Unlike acrylics and other modern materials, oils have largely not undergone heavy redevelopment to improve on traditional performance. (Paradoxically, many experimental artists favor traditional oils and actually love them for their limitations as well as strengths.) It's the nature of oil paint to behave this way when colors dry prematurely over semi-wet paint. I really think a medium with a moderate (not fast) drying rate will help enormously.

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    Sorry to join the discussion late. I suspect what's been described is the result of upper layers skinning over quickly while the paint beneath is permitting movement. The fact that the problem manifests late in the process is a telltale sign. I have seen this before, when artists have layered paint with a fast-dring alkyd medium on top of touch-dry (but still uncured) oil colors that have a high oil content. The top skin can be scratched off easily at first, but as it stiffens and the lower layers proceed toward a full cure, the film becomes more mechanically durable. Whether the final bond is optimal is another matter, but the tendency to easily scrape away from lower layers does lessen as the film dries.

    I think the addition of a medium that dries at a moderate rate, especially in the upper layers, would make a positive contribution to this process. This would help top applications keep up with dimensional changes in lower layers and should promote better adhesion in complicated layering. There are also other advantages to using a medium in layered techniques, in terms of handling, and achieving better control over the appearance of colors.

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    ​Your question raises many others before really being able to address it. When you see failure in the thick areas, is it a clean cleaving between layers, or failure within that actual paint itself? What is the substrate? How long have the films dried? Are you using mediums, solvents? Different paints will take different lengths of time to fully cure and reach maximum adhesion, so knowing some of those parameters is important to knowing if you are testing too soon. It would not be crazy to need to wait 6-12 months or, in thicker applications, even years, before full adhesion is reached.

    Would also be good to know why you suspect layers are not adhering? Adhesion issues in the short term are not a problem for most best practices when paints are allowed to cure naturally, but it sounds like you might be putting the films through some sort of extreme stress early on or trying to push techniques or processes into areas that oils are not well suited for. Linseed oil in the end is not a very strong adhesive and can only take so much stress or strain before breaking - which might be mistaken as a form of adhesion failure - versus true delamination where one layer truly comes free from another.

    Finally, just in general, crosshatch adhesion or the simpler "x" field test are really the standard for interlayer adhesion testing for something like this. Other alternatives, which involve embedding a material between layers, or gluing a metal disc to the surface with epoxy and pulling these strainght up are meant more for pure test panels for specific applications and not an actual work in progress. So you are on the right track - but it might be that the test is too strenuous for the stage at which it is being used.

    Look forward to more information to see if we can help.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    Thanks Kerith! This is why we have health and saftey experts on our board :)​

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    Great question!

    If using a respirator when working with pigments, you should be using a HEPA also called a P100 particulate filter.  It's the SIZE of the pigment particles (not the type) that determines the type of filter you need (You'll also see 99 and 95 rated filters, but they won't provide enough protection). P100 filters are the best option since the N100 and R100 have time and material restrictions. You probably will recognize the pink/magenta color of HEPA masks. N and R are cheaper but you have to be aware of whether you'd have oil particulates present (need to use R) and that you only use them for 8 hours and then they must be discarded.

    If you are using chemicals along with your pigments (e.g., turpentine) you'll need the appropriate chemical respirator as well (there are combo chemical/particle respirators available).

    However, many pigments are ground so finely that even a HEPA-filtered respirator will not trap all the particles. For that reason, and all the other hazards that are associated with working with pigments (see below), the best and safest practice would be mulling the pigments (or at least the handling of the dry pigments) in a glove box or bag (a sealed enclosure that you just stick your hands into).

    Breathing in the pigments is just one of the hazards of mulling.  The following is abbreviated from "The Artist's Complete Health and Safety Guide" (p 112-113). 

    - Not only can the particles be inhaled but they easily cross-contaminate other surfaces, so proper hygiene is import (hand washing, not eating or drinking in work areas). 

    - You should be wearing gloves and other protective equipment that are used only for that purpose (don't leave the studio with them on) and can be removed once contaminated. 

    - Work on easy to clean surfaces and wet clean surfaces--pigments can be so small that they are not collected with HEPA vacuums. 

    - Check with your local hazardous waste centers and see how everything must be disposed of as hazardous waste.

    - If you're using a lot of heavy metal pigments regularly, it would be wise to have yourself tested for exposure (at least once a year). 

    - Also, finely powdered metallic pigments (like aluminum and bronze) can be flammable and explosive.

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    ​I think that it would be best to leave this question for moderators who work for the fine art paint industry as they deal with this testing on a regular basis and will be aware of the most current thoughts on the subject.

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    ​Great question....we have a bit of information about masks in our health and safety document which can be found in the resources section here. The N-series is what you should likely use....you can find such masks at Lowes, Home Depot, etc. and even online of course. I will also reach out to some of our health and safety experts on this as well. Also remember to wear goggles and to dispose of residue properly!

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    My understanding of the Carder medium is that it leverages the powerful antioxidant property of eugenol in essential oil of clove to inhibit drying. Eugenol is more powerful in this respect than preservatives like tocopherols, which are used to prevent rancidification of fats through the same mechanism. I suspect the Carder formula exceeds preservative-level concentrations that would be found in edible fats, though I don't think most clove oil is standardized for eugenol content.

    Providing a high-oxygen environment for a painting executed with large amounts of clove might optimize any autoxidation that was still possible, but in a closed environment, the essential oil would be much slower to leave the film. Maybe exposure to a current of moving air to chase off the essential oil as it evaporates would be more effective in restoring the ability of the film to dry. I'm sure an inert gas environment would retard drying.

    A few thoughts on this proposal:

    -Heavy manipulation of the drying rate of oil paint is risky.

    -Creating a high-oxygen environment can create a fire hazard, and (just guessing here) may affect the support material.

    -If oil paint in a jar with some air space hasn't formed a skin in two years, I would imagine oxidation has been virtually arrested.

    -Preserving batch-mixed oil colors is better done with collapsible tubes to exclude air, rather than adding preservatives.

    -Prevention of skinning can actually speed internal drying, depending on how it's done. Industrial paints often include an anti-skinning ingredient to ensure through-drying. One product on the market for speeding drying of artists' oils includes an anti-skinning agent as well. My point here is that, just because paint may seem wet and skin-free, doesn't mean it hasn't undergone oxidation.

    -This system (heavy application of retarders and alternating oxygen-rich and oxygen-starved tent environments) sounds impossibly complicated for even a sophisticated artist's studio. 

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    ​Slick as in reflective and mirror smooth. You really do NOT want that for your size layer as there should be enough mechanical "tooth" to the surface for the subsequent oil paint layers to successfully adhere.

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    Some of these are well answered in our resources section about oiling out. I am sensing that you are restating these questions because you do not really like the answers we have provided ;) I will briefly address each of your questions.

    The fat over lean “rule” is an over simplification. The important notion is more rigid and brittle under less rigid and more flexible. In this instance, this is not the important factor. If you rub walnut oil into the acrylic dispersion ground and paint into it before it has dried, the oil becomes incorporated into the paint and is not a discrete layer any more. We really advise to not apply oil as a coating that is allowed to dry before paint is applied. The reasons for this are enumerated in our resource section. A properly dried paint film should be resilient to the application of additional layers of paint containing solvents as long as the solvent choice is not too “hot” or slow evaporating. This is one of my issues with spike oil which evaporate so slowly that is can dissolve paint films that have set for a reasonable amount of time.

    Bodied oils tend to provide a slightly sticky surface after the solvent has evaporated. This may or may not facilitate your intended effects. In addition, stand oil is less yellowing that unprocessed oil. There is nothing wrong with using walnut oil, as long as you are going to paint into that oil and cover it completely with layers of pigmented paint. I sense this is not what you want to hear.

    Unfortunately, it is a bad idea to leave dried oil exposed, even over dark paint layers. It will yellow, but also become turbid over time. These areas will eventually be seen as slightly brownish-green. No, it will not be as visually disturbing as exposed oil on light colors or white, but it will still become visually apparent.

    There are too many factors here to give an exact timeframe for yellowing. Again, I am sensing that you want to hear that if you have not seen this in X amount of time, there is not a problem. I cannot offer that assurance.

    Unless the effect created by additions of wax are essential to your aesthetic aims, I caution against incorporating it INTO oil paint. There is not a real problem with this but if large amounts are added, the work should be treated as something different than a traditional oil painting and certainly information about the media and wax should be noted and retained on or with the painting. You should also seriously deliberate whether to varnish such a work. Wax will remain eternally soluble in mild organic solvents making it difficult to remove a discolored varnish if a substantial amount of wax has been added.

    If you oil out into a couch of wax you are likely going to slightly dissolve the wax into the oil. This would be preferably to having a discrete wax layer between layers of oil paint. Wax interlayers could be “undercut” during varnish removal, which could scale away the uppermost oil layer. This is the worst-case scenario but it is certainly possible with wax interlayers. Again, please record you working materials and layering on the painting if you are going to use this technique.  You could also make a note on your painting that you would prefer that your paint not be cleaned in the future due to your medium or varnish decisions. As always, it is better to provide future conservators with more rather than less information.

    I hope this was of some help.

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    Shellac is not optimal but would work for the purpose you are suggest. It is essential to not create a slick coating and make sure that it is functioning as a size. The deterioration of shellac is probably less of an issue in the manner in which you are using it as it is completely hidden by subsequent opaque paint layers and is far less likely to suffer from vis light and UV degradation. Again, it is not a perfect solution, but will probably suffice if not applied to thinly or thickly. Shellac’s non-aqueous nature means that initial warping minimized. I would size both sides (and the edges to be thorough). One could substitute the acrylic resin B-72 (in xylene, acetone or ethanol/acetone mixture) for the shellac. Proper ventilation is necessary for these solvents. The B-72 would very likely behave similar to the shellac but it is a more stable resin. Again, this may be of a lesser issue when buried under layers of paint.

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    ​If paint is lifting when oiling out, the initial layer is probably not dry enough yet. You may want to try a different medium, maybe alkyd-based. For a very long time, artists have employed mediums that render paint faster drying and, when touch-dry, less vulnerable to staining and re-wetting. The de Mayerne manuscript describes (vaguely) the "Amber Oil of Venice" that was used in the Gentileschi studio for flesh and white passages, to facilitate prompt overpainting and reduce staining of light colors. There are lots of factory-prepared mediums that deliver these benefits today. A medium that imparts gloss will also reduce sinking of colors.

    If the paint film contains significant amounts of wax, I would not advise oiling out or any heavy manipulation. Wax tends to dull a paint layer so if you are having difficulty achieving deep darks, wax may not be the best choice.

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    Must it be an adhesive? Sometimes I favor mechanical attachments (e.g. screws, wires, etc) over adhesives specifically where heavy 3D elements on rigid panels are concerned​.

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    Brian, interesting point about the assumption that Oil of Spike Lavender is necessarily less toxic than OMS. Where lavender essential oil is concerned there simply isn't anything like the record of heavy, long-term exposure to spike like there is with turpentine. We know a lot about risks associated with turpentine largely because of its extensive history in the ceramics industry, where there was widespread, heavy exposure over many years, and a detailed record of the consequences.

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    ​Stand oil is different...it tends to yellow less, takes longer to dry, and creates a more flexible film. The problem is some highly viscuous stand oil mediums are not easily thinned using Gamsol as a solvent...You might find our document entitled "Mediums and Additives" in the Resources section of interest as we go into some detail on the various types of oils used in painting.

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    ​While we recognize the desire by artists to paint directly on raw aluminum - and will provide recommendations if they insist on going there - we feel that raw aluminum is inherently reactive and ultimately best practice is to either have it primed or with a protective coating in place. You can read about our best recommendations for either approach in the following article:

    http://www.justpaint.org/painting-on-metal-an-introduction/

    I would also point you to the fact that Dibond does make an aluminum panel that has only a clear protective coating and so does appear quite metallic while still being protected from oxidization or corrosion. Preparing that surface for painting would be the same as with the white polyester coated panels you usually find.

    Hope that helps.

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    ​We have included some suggestions on how to prepare Aluminum substrates for painting in our "Rigid Supports" document which can be found in the Resources section (Just scroll down to the "Aluminum" section). I also think using acrylic medium would be fine to apply to the surface to use as an "adhesive" as long as you clean the surface well and impart a bit of tooth. Perhaps our colleagues who are experts in acrylics can weigh in here as well....

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    Great questions. While the UVLS system imparts a slight yellow cast to a clear coating, as you correctly stated, it is essentially undetectable at the thicknesses a varnish is applied at, so you can essentially consider them clear. However, there are definite reasons you would not want to add UVLS to oil paint directly, nor ever blend a varnish containg UVLS to oil paints as a medium, or - at least in terms of our own MSA Varnishes - paint on top of them. That last point is something we touched on recently in an article published online:

    http://www.justpaint.org/why-oil-painting-over-msa-or-archival-varnish-is-not-recommended/

    The essential reason you should never add UVLS to oil paint is that it will inhibit the drying of the oils and cause them to remain sticky and uncured. The UVLS system not only filters out UV radiation, but is also designed to absorb the free radicals created in the process - however free radicals are precisely what is needed for oil paint to crosslink! It is as if you added in a permanent regenerative anti-oxidant which, well, stops oxidization.  Not a good thing with oils and can cause major problems.

    On a secondary note, we have found that UVLS has never been as affective when blended into a material versus applied up on top. - at least in the case of lightfastness protection. Unless one is using a very binder-rich system, you just do not get the same concentrations as a separate varnish layer can provide. But of course, because of the above issue, this secondary one is moot as far as oil paints are concerned.


    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors


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    Hi

    There are a couple of separate issues here. First, there is no evidence to suggest that oil of spike is less toxic than Gamsol, which is a very pure odorless mineral spirits (meaning that aromatics and other more toxic fractions have been removed). These highly refined aliphatic solvents are probably the least toxic organic solvents that are miscible with oil paint. It is important to realize that there is a very different “feel” under the brush between “regular” mineral spirits, OMS, gum turpentine, oil of spike, etc. This may be mitigated, obliterated, or augmented depending on what other components are added to the diluent.

    Spike oil is probably most useful due to its very slow evaporation rate, this can be exploited for certain technical effects. It is not without its dangers, though. It’s very slow evaporation rate also means that using this solvent in subsequent and upper paint layers can allow for the biting into and disruption of lower layers. Unlike paints like gouache, which can be rewet many times, biting into and dissolving semi-dried oil paints irreversibly diminishes film strength. This is not to say that one cannot use oil of Spike responsibly, but I would restrict its use to ala prima or to paintings with relatively few and well-dried layers.

    As to over use of diluents contributing to a weakened oil film, think of it like this, while in theory a diluent is not changing the percentage relationship between pigment and binder, there is a point where pigment particles are so separated and the binder so attenuated that the resulting paint film is friable and underbound. This situation is not uniform for all media. It is important to realize that drying oils are not really great adhesives and their ability to bind pigments is rather limited. Acrylic dispersion binders, on the other hand, can be thinned to a great degree and still adequately bind the paint film (within reason).

    As to walnut oil, it produces a slightly less resilient film than linseed oil. Linseed oil certainly creates the strongest paint film, but walnut oil may skin less readily, resulting in less wrinkling of thick paint films. This is not universally agreed on and some blame the paint defects in early 16th century Italian oil paintings on their use of walnut oil. We at MITRA feel that, until there is conclusive evidence, walnut oil it is a perfectly reasonable binder for oil paint.

    As far as “less yellowing” much of the current thinking about this phenomena is that the three major (highest grade and selected for color stability) drying oils do yellow at different rates, linseed the soonest and poppy the last, but that, over time, they all yellow to somewhat the same degree. With this in mind, we feel that it is probably more important to choose drying oils based on their handling and film forming qualities.

    I hope that was of some help.

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    Is the student using anything other than water to thin colors? I have read about paint loss in watercolors due to excessive use of additional Gum Arabic. ​

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    ​I would like to add that while many industrial products are descriped as non-yellowing, this is seldomly sticktly true in the sense that artists mean. Very slight ambering would be a non-issue on a wooden oject but could be highly disfiguing on a fine art piece, especially if that work contained cool colors like blues or cold grays.

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    ​The following is a comment from objects conservator Craig Deller: The varnish popularized by such videos and woodworking magazines tend to be intractable synthetics, many of which we don't want on paintings (or much of anything else). While all resins are naturally glossy, they can be brought to the "water-wet" appearance. Depending on the texture of the painted surface, you may be limited. However, if the surface is flat enough to warrant the kind of mechanical action as in the video, then I would suggest a French Polish technique. While French Polishing is normally associated with shellac, it may be too amber in tone for the desired results (bleached shellac is far too unstable given the process to remove the colorants natural in shellac. I have found that by using the FP technique with B-72, or any other alcohol soluble varnish, can be brought to the water-wet shine. If this interests you, I can elaborate.

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    ​To answer your very last question the answer is: not really. I am sure some of the moderators will chime in here but I would be remiss if I did not state the obvious which is this....if you attempt to buff down a painted surface on dibond you truly need to make sure your paint layer is as flat and level as the coatings on top of it. Meaning no impasto...not even at a microscopic level. Maybe you are not to worried about buffing down to the paint layer below but that is a huge concern. I will reach out to some of my objects conservator colleagues as they will be far more informed about these types of coatings than I am...

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    ​Hi Koo...it seems that this problem has stumped a number of us moderators. There are so many variables here...and reassure your student as he seems to have been trying to tackle them one by one (moving away from tap water to distilled water). I think at this point the only words of wisdom left to give is to simply encourage your student to continue down that path. I am sorry that we could not really find a solution here but please keep us updated if you can.

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    ​Not a problem - and makes sense. It is definitely true that this has the great advantage of being a public repository of knowledge. 

    One great tip and trick is that we find wet sanding is usually the most effective way to sand acrylics since it reduces the heat from friction and produces a smoother more even result. 

    Let us - as in here at MITRA - know how things go.

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    ​Hi Koo -

    Of the options you presented the Hard Sandable Gesso would be your best choice, especially if sandability is desired. Just keep in mind that in the process of sanding you will also likely reduce the tooth of the Pastel Ground to something closer to....well, the Silverpoint Ground or the Hard Sandable Gesso! As for proportions for tinting it, I would think 3 parts Pastel Ground to 1 part Hard Sandable Gesso would be more than enough to get a bright white. Could likely even get away with a 10% addition. 

    It is true that the Pastel Ground has more tooth than the Silverpoint Ground - something obviously needed for Pastels - but that tooth I think will also interrupt having a smooth, textureless mark - if indeed that was desired. But certainly it will create a darker mark by grabbing more of the metal.

    The Silverpoint Ground can be sanded.....if needed.....but it is also very thin in viscosity. Really essentially ink-like. So it lays down very smoothly. Something that is ideal especially if wanting to prepare a sheet of paper and preserve its feel. In that sense it is close to how it feels when preparing a surface with Gouache or even a chalk ground.

    Hope that helps. And never hesitate to just reach out to Golden directly if you have questions about our products - we are wickedly fast in responding. :)

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    Da Vinci is known to have broadly manipulated paint with his fingers in creating the "sfumato" effect. ​It seems to me that this approach has something in common with "oiling out".

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    When applying medium or thinned oil to the dry painting, it's best to use only the minimum effective amount necessary to achieve pictorial objectives. One of the main reasons artists oil out paintings is to restore the wet appearance of colors, which makes it easier to duplicate mixtures in a subsequent session. A different painting medium might reduce the amount of color change from wet to dry, and eliminate at least some of the need to oil out. Traditional plant resin varnishes, particularly ones that yield a "candy" gloss, tend to yield good results in this regard but may not prove stable and durable with age. Some alkyd-based mediums can help preserve the wet-mixed appearance of colors, without the drawbacks of materials like damar and mastic.

    Other reasons one might oil out a dry picture are to facilitate suave brush movement without "break" in the strokes, and to meld layers seamlessly together. Fully loading the brush can promote smoother movement on a dry surface (to a degree), but most artists who routinely oil out between layers will probably not be satisfied without first lubricating and reducing the absorbency of the dry surface.

    When oiling out, the surface should not feel extremely wet- use only enough to allow a well-loaded brush to glide across the surface. It only takes a small amount of oil to facilitate subtle blending and other manipulations of the still-wet paint. 

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    To be clear, it is always important to use fresh paint. Ralph Mayer has a very good section on this in his The Artists’ Handbook. The degree of importance varies from medium to medium. Obviously, for traditional watercolor and gouache, the issue is of little importance as the paint is completely resoluble. It is paramount in egg tempera.. It is in the middle for oil paint. The issue is that you want the paint to go through its whole drying or setting curve in place and not interrupt that, which can diminish adhesion. This is different from adding partially pre-polymerized/oxidized mediums like thickened linseed oil as these are in addition to the amount of binder need to adequately produce a serviceable paint.

    While there are certainly examples of modern and post-modern artists incorporating paint skins into their works, I would caution against it unless that is the specific effect that you are searching for and not just a result of your attempts at economy.

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    ​We feel that it is "ok" to use the paint inside IF it is still wet AND if you do not incorporate any of the "skin".....the latter is harder to do. Realize that even though the paint beneath the skin, even if it is still wet, has probably begun to oxidize to some degree but you can still work with it to a degree.

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    I have heard this problems raised, for many years. To begin, if the paper is thin and it is from China, it may be cotton. It could be Kozo/Gamp/etc. (Japan/Korea) but real rice paper is stiff like papyrus. Mounting thin Asian papers is an art form, since it entail using degraded starch (furunori), which may have been stored under water for many years, but more importantly, it employs a complex system of papers and fabrics that have been dried under tension and which form a counterbalanced system that can be easily disturbed by the addition of moisture. If a western equivalent were to be designed, it would also need counterbalancing, since paper (four ply board) can warp Dibond that it has been adhered to. One possibility might be: Dibond with lignin-free blotter paper bonded to both sides with acrylic medium. Methyl cellulose can be applied to the blotter paper, and allowed to dry. The Asian paper is humidified, with Hollytex and blotters and is smoothed, damp, onto the M C covered surface and allowed to dry. This would Have to be tested, since it is only an idea, but traditional asian methods can only be undertaken by someone schooled in them. 

    Alternately, the Asian paper can be sandwiched between an acrylic sheet and mat board, with a rigid backing board like Dibond, D-lite, or Pro-lite to keep the pressure consistent.

    Hugh Phibbs

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    ​Hi there - when you say that you want to protect the paintings, do you mean while being exhibited? In storage? The process you're talking about is called lining, and it makes sense that you would consider doing this - however, it is a process which is quite tricky and could be disastrous to attempt yourself. My suggestion is to either find a paper conservator who will line the paintings for you, or to mount the paintings on (acid free, high quality) rag board using Japanese paper hinges. Dry mount is difficult to remove, should you wish to do so in the future, and wet mounting yourself is likely to be problematic. Hinging with Japanese tissue and wheat starch paste would be gentler on the paintings and would allow for a window mat which would protect both sides. Another option would be to store the paintings between layers of acid free tissue, inside appropriately sized folders made from board or heavy paper stock. I can provide photos if any of this is confusing.

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    ​Yes precisely what Sarah said....also there have been several threads thus far about zinc and its related issues (accompanied by practical suggestions)....if you type in the word "zinc" in the search field many of these should come up. Let us know if you have any additional questions after reading through some of them.

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    ​While there is a longish tradition among some suppliers of preprimed canvases for using zinc, with everything we currently know about the embrittlement of zinc oxide when used in oil paints, I would not recommend its use in a ground - especially if stretched. If you felt compelled to use it, then mount it to panel at the very least, or use it for casual studies. 

    That said, a high-end supplier like Claessens has a long history of making canvasses using zinc as an initial layer, followed by titanium white, and I do not know of a study that expressly looked at how their canvases have fared. Perhaps that particular layered structure lessens the concerns? Don't know. But again, to err on the side of safety, I would personally hesitate to recommend any ground with zinc.



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    Lead is the primary source of chemical, as opposed to physical, increased transparency in old master paintings. However, zinc oxide also forms metal soaps that can increase transparency, as can probably other reactive metals in pigments, but to a much lesser degree. So, in the absence of these issues, chemically induced increased transparency is the result of a slight elevation in the refractive index of the binder over time. This is certainly a secondary and a lesser cause.

    Probably, one should not worry too much about this. Frankly, you probably see more of a change when you varnish your egg tempera paintings. I would still caution against working on very dark grounds where a slight increase in transparency would create a profound change, unless that process is necessary to your aesthetic aims.

    I should also mention that there are also physical causes for this visual defect. Lower layers are sometimes more visible than originally painted due to the abrasion of the surface layers from poor restoration procedures (eg some of the overly green faces seen on early Italian tempera paintings). This can be easily avoided by proper care and storage and only using qualified conservators to conserve one’s artwork.  

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    The primary mechanism behind increased transparency involves the formation of lead soaps which is due to the complexes formed between the free fatty acids in the medium and the lead carbonate. There are secondary mechanisms as well but they play a lesser role. So fatty acids are in abundance in both oils and alkyds. Transparency can therefore occur more readily in oil films (and probably alkyds) that contain lead white. Increased transparency can also occur in egg tempera but to a much lesser degree. Because shadows in dark areas would inherently contain much less lead white they are unlikely to become more transparent beyond the slight change in refractive index of the binder. Even this change would be somewhat mitigated by the fact that dark transparent layers tend to be "fattier" and therefore tend to darken over time....this counteracts to some degree any increased transparency that may occur. Finally, one might then ask: why do we now see underdrawing under areas of red lake when it was likely not initially visible? This is usually because painters that exploited this technique (early Netherlandish/Flemish painters) often covered their underdrawings with a lead-white containing imprimatura layer, a layer which over time eventually becomes more transparent. This is yet another thing to consider when loading your oil paints with lead driers...to my knowledge there has been no research into whether an abundance of lead ions from driers within an oil or alkyd matrix would lead to an increase in transparency...but the chemistry behind this mechanism would be the same and therefore leads me to believe that it very well could.

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    ​Thanks for the post. Lets hope others are aware of the discussion. Here are a couple of threads on  similar subjects.

    https://www.artcons.udel.edu/mitra/forums/question?QID=226

    https://www.artcons.udel.edu/mitra/forums/question?QID=135

    You may also want to track down this paper that is referenced at the end of my reply..

    Author: Habgood, Sean Corporate Author: Queen's University. Department of art Title of Source: Determination of the appropriate support characteristics for the lining of paintings Publisher/Distributor: Queen's University Publisher/Distributor City: Kingston Publisher/Distributor Country: Canada Date of Publication: 2003 Collation: 39 p. : ill. ; 28 cm. Language Text: English Language Summaries: English References: ca. 60 bibliog. refs. University: Queen's University University Location: Kingston, Canada Degree Level: Master of art conservation Subject Keywords English: Painting;Lining;Materials;Textile;Canvas painting;Examination;Tensile strength;Stress;Strain;Measurement;Qualitative analysis;Test;Linen;Synthetic fibre;Synthetic resin;Evaluation;Research project Subject Keywords French: Peinture;Doublage;Rentoilage;Produits;Textile;Peinture sur toile;Examen;Résistance à la tension;Contrainte;Déformation;Mesure;Analyse qualitative;Essai;Tissu de lin;Fibre synthétique;Résine synthétique;Evaluation;Projet de recherche Subject Material Test: Dacron monofilament sailcloth;White polyester;Brown Sunbrella;Linen;Cuben fibre cloth;Beva 371 Abstract: This research project examined the requirements for a lining material used to line painting on canvas. A good lining material has high chemical stability, a high Young's modulus, high strength, non-hygroscopic properties, good chafe resistance, and desirable properties such as a smooth surface, good adherence to lining adhesives, good transparency and isotropic behavior. The testing started with the examination of a painting's substrate and quantifying what it's needs were. The lining materials typically used in the past do not meet most of these criteria. Several materials were compared to see which of these materials would best support a painting's substrate. The materials that were looked at included Cuben fiber, Dacron monofilament sailcloth, white polyester, brown Sunbrella, and linen. The testing looked at the structural needs, the aesthetic concerns and real world applications. Cuben fiber cloth's properties meet more of the requirements for an ideal lining material then any cloth used today. Originating Institution: ICCROM Location of Document: ICCROM ICCROM Shelf: Kingston Report 288 Literature Type: Monograph:Thesis Bibliographic Level: Monographic BCIN Number: 427905

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    ​Hi Koo -  

    First there's a pun in that "short" greeting which I will leave untouched but it does make me smile :)

    When you say it happened sometime after the paint was applied, can you give a sense of how long the period was? And how were the pieces stored or kept during that time? Anything in contact with the surface? And as was mentioned, knowing the particulars of the brand of paint and the paper would help.

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    ​Little to add that has not already been covered by Brian, Kristin, and Matt. However one way to test if you have over-thinned paints is to use a q-tip and some OMS after the color has thoroughly dried - say two weeks - and then see what degree of color lift you get when gently rubbing an area. If color comes off easily, that's a problem. If it takes some time or work, then at least one can assume that subsequent layers might lock them down.

    Also, keep in mind that the amount of thinning and the appearance of a matte film will be pigment dependent as well - with very small particle pigments requiring more oil to pigment ratio to fully wet out and so likely more tolerant of thinning. Larger particle colors will by contrast appear matt more easily.

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    What is the specific objective? Is the purpose of the experiment to confirm reports of defects in paint films containing these oils? I wouldn't go into this with the realistic hope of yielding paint suitable for permanent art. Anyway, if the oil used as the paint vehicle is a hardware grade product, it might not be of standardized quality, and because of this, it might not be possible to duplicate results if you did get one sample that looked promising. 

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    Imagine paint as analogous to a brick wall, with the pigment as bricks and the oil as mortar. Too much water in the mortar leads to lack of cohesiveness, weakly bound bricks and ultimately a failed wall. In paint, excessively thinned vehicle cannot maintain envelopment of the pigment, so there's nothing to stick the particles together. When the solvent evaporates, there might be the same amount of materials, but just like a failed wall where all the bricks and mortar are still there, cohesiveness and orderly structure are lost.

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    ​Hi Koo,

    That is a strange situation.  I'm wondering if there is something on the student's brushes?  Are they using a fixative?  Is the student painting in a studio where you can observe them?

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    A couple of things I notice upon examining the photos: One of the images appears to show a canvas-like texture in the support. What is the support material? Is it paper, and if so, which brand? Also, it looks like the "vermiform" pattern manifests over both paper and the masking tape at the edges. That makes me think there may be an issue with the binding power of the paint. Do we know which brand of colors, and what the specific palette is? Are some colors more affected than others?

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    Probably, it would be difficult to calculate the precise percentages that you are looking for. There are just too many variables. Each pigment has a different oil absorption requirement. This is the minimum to create a workable paint. However, manufacturers will likely have to include a bit more than this to make a paint that does not require onerously long milling as well as a paint that can be thinned without causing the issues you mention. Each manufacturer will do this to a different degree. The highest-grade paints with the least amount of stabilizers/fillers could probably be thinned to a different amount than those containing far more oil and are chock full of aluminum stearate. Student grade paints, a different amount. Very well made hand-made oils an even different amount. The short answer is no.  It is likely adequate to just never thin your oils more than a thin cream or whole milk consistency.

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    ​Hi Koo...there is a way to add images. If you can do so that would be very helpful!

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    When overly-thinned paint yields a dull, lackluster appearance, it's because the viscosity of the paint vehicle has broken down. When this happens, the envelopment of each pigment particle is lost, and along with it both binding power and the essential optical function of the oil.

    "And I've come across the idea that oms evaporates fully and thus doesn't alter the lean-ness of the paint once it's gone, is this true?"

    Kristin, I was thinking the same thing you mentioned in your reply to this question. In theory, if the thinned paint were applied to a completely impermeable material like glass, one would expect the oil-to-vehicle ratio ​to remain the same after all solvent has evaporated. Since a primed canvas is porous and absorbent, however, and because staining appears on the back of the canvas, it seems reasonable to assume that some of the vehicle has been taken up by the ground and support material.

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    ​Here are a couple of references to two of the oils mentioned:

    "Tung oil appears to dry in about two days in moist air, but the resulting film is always wrinkled or cracked and uneven. In dry air about fourteen to twenty-one days are required and a smooth, coherent film is obtained. In either case it takes twenty-one to thirty days for the full gain in weight (12.9 to 13.3 per cent). From this it appears that tung oil is really a slow-drying oil, and that the rapid rate of drying in moist air is not 'drying' in the usual sense (i.e. oxidation and polymerization), but a colloidal change in which moisture acts as a coagulant... It is as unsaturated as linseed oil, but has considerably more tendency to gelatinize or separate in the heterogeneous phase, so that films produced are frequently dull or mat. It also yellows badly and may cause skin diseases."

    "(Perilla Oil) dries quickly but gives a dried film which is somewhat marred by irregular markings and spots."

    - "Painting Materials: A Short Encyclopedia" by R.J. Gettens and G.L. Stout

    "Chinese Wood Oil (tung oil) cannot be employed despite varius favorable qualities, because it forms an untransparent film when it dries, and may also cause skin diseases. Furthermore, it yellows badly."

    -"The Materials of the Artist and their Use in Painting" by Max Doerner

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    Simply put, I would caution against this experimentation in one’s artwork. In general, these oils either create weak films, dry very slowly, or yellow too strongly, usually more than one at the same time. Ralph Mayer does discuss a number of these and enumerates their shortcomings. I sometimes find Mayer’s pronouncements a bit too conservative and sometimes slightly out of date but agree with him on these issues. Finally, why take the chances when alkali refined linseed oil is so cheap and available. If you do decide to experiment, do simple paintouts which would not be missed if they failed and please report your results back to us here.

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    ​A watercolor-like wash is not really recommended HOWEVER if you are applying fatter paint on top of ALL sections that possess this thin layer then you will likely be fine...you might try adding slightly less solvent and "thinning" out simply via manipulation of the brush. This may mitigate the strike-through that you are seeing on the reverse of the canvas. The latter tends to occur when the size and/or ground is not adequate and/or you are overly thinning your paint with diluent. OMS is completely appropriate to use for oil paint as long as you are not using certain additives such as natural resins or other materials that are not soluble in OMS.
    As for this question: "If this thinned layer leaves the ground with much tooth available for thicker paint to adhere to, would delamination problems persist." We are not sure what you mean by too much tooth. In general tooth implies that your ground is textured enough to adequately allow for adhesion of subsequent layers. 
    And this question: "And I've come across the idea that oms evaporates fully and thus doesn't alter the lean-ness of the paint once it's gone, is this true?" Solvents that leave no residue do not, in theory, alter the lean-ness of the paint layer. However, one could still potentially overly thin an oil paint layer to create an underbound surface to begin with.

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    ​Thanks Sarah these are all great suggestions....as a conservator I would support using any of these materials over board made from wood pulp.

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    ​Hi -

    Thanks for the clarification. Could you point to a link for the product you are looking at? And in terms of solid panels, would you consider aluminum composite panels, such as Dibond? They are very dimensionally stable and should have excellent long-term durability. In terms of lightweight paper-based alternatives - although I realize what you are thinking of is something different - if you have a good conservation or framing supply retailer you could look into things like the following:

    http://www.talasonline.com/Heritage-Corrugated

    http://www.masterpak-usa.com/cat_214_multiusebd.htm

    http://www.talasonline.com/Tycore-Hexamount-Panels

    Also, while there is some back and forth on whether Sintra (a closed cell rigid PVC panel)  raises any conservation concerns, you can still find many sources that recommend it for use in museum storage and case construction, and we have had good results using Sintra and Sintra-like panels with acrylics:

    http://www.conservation-wiki.com/wiki/Sintra

    http://www.sintrapvc.com/

    And finally, there are some forms of MDF that do not have formaldehyde and likewise have found some acceptance in conservation circles, such as Medex:

    http://www.hardwoodweb.com/architectural/docs/MedexSpecApril08.pdf

    But whether that or a similar product is available where you are is another matter.

    Hope some of these alternatives help.


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    ​Hi - There is really nothing redeeming about generic, brown, common industrial cardboard - if that is what you are referring to - other than being cheap, and a part of that inexpensive cost is based on not needing to produce a product with much longevity. It is invariably acidic and with a high lignin content. However 'cardboard' can also be a catchword with a broad reference, and the following document does as good a job as I have seen in describing what you would want to look for in a 'cardboard' that was acceptable for use:

    http://preservart.ccq.gouv.qc.ca/documents/carton_en.pdf

    And, as a rule, if the manufacturer is unwilling to speak to the content of their product at the most basic level I would recommend moving on to something you can have more confidence in.

    Also  - and I say this with all due respect - why on earth would you want to use something where you would consider going through all these steps

      • "saturated the cardboard with something (gelatin/methylcellulose/PVA/wall paint primer?), then
      • gave it three layers of gloss medium (first diluted 1:1), then
      • put on two layers of acrylic ground

        and then painted on it? I'm not sure if three layers of medium plus two layers of ground wouldn't be too excessive."

    rather than simply using something suitable for artwork at the start? Such as museum board or other types of thick, stiff boards made for artists? I ask because going through all the steps above just to try and make a commercial cardboard suitable seems like a lot of work and in the end any cost savings would be lost and you would still have something that is suspect.

    Putting all that aside, and assuming there is something intrinsic in this particular cardboard that compels you to use it, then I do think applying a 3 coats of acrylic medium followed by 2-3 coats of an acrylic gesso would act as a sufficient barrier to protect the painting from the substrate. I do not think that literally saturating the entire piece of cardboard is necessary and if you felt worried about its physical durability, then adhering it to something more rigid such as an archival foam board or an archival corrugated board like Coroplast might be something to look at.

    Do let us know what the needs are that you feel this cardboard meets as I am sure there might be a less problematic material we could suggest as a starting point.

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    Hi

    First a bit about cardboard. If it is standard cardboard the issue is not the cellulose but the lignin that is the issue. Low-grade wood pulp paper and board deteriorate and become yellow and brittle very quickly (think newspaper). I really first have to ask, why cardboard? If you are thinking the standard variety cardboard, I cannot really think of any great remedies for it deficits. Is it the corrugated surface topography? If so, that surface would likely be removed in this future hypothetical “relining” (actually that would be a transfer and it would require hundreds of hours meticulously removing the old cardboard under a microscope using a scalpel). The only way this separation could be made easier would be to have an easily reversible interlayer. Certainly, the board could be “encapsulated” in layers of more stable materials. Both of these options are possible, but this still begs the question, why cardboard? The only reasons I can think of are topography, weight, or economy and there are probably better materials to achieve these qualities if we understand your reasoning.  

    If you are interested in both the surface topography and the light weight, I would suggest that you use acid free blue board which is used for more archival purposes. If you really like the color of standard cardboard (although this does not seem to be the impetus for using it as you mention the willingness to apply acrylic gesso) I would coat the blue board with a couple of layers of acrylic dispersion paint of the appropriate color.  

    Could you give us the reasons for the choice and perhaps a more suitable answer can be formulated.

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    Hopefully someone who has tried this painting technique, step-by-step, will weigh in eventually....but unless I am mistaken none of the moderators have attempted this unique technique of painting....therefore it is difficult for us to give sound advice on what to do and what not to do. I do hope you will write back in and tell us how your experiments go...if problems arise we can go through the list of materials you decided to use as well as your technique...but hopefully none will!

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    To the OP

    You can certainly use industrial products in your artwork but you should realize that they were formulated for a very environment and expectation of longevity and may or maynot fulfill your requirements.

    This is from MITRA's FAQ section:

    Industrial materials made to withstand outdoor (and even indoor) conditions were formulated for very different purposes than traditional art materials. There are many choices that paint manufacturers make that affect the outcome of a given product and paints produced on an industrial scale often use additives that are relatively economical and/or are the easiest to incorporate into the paint formulations. These additives can aid in creating a more workable paint and helps the paint film to withstand severe weather conditions and extreme exposure to light; however, these additives (i.e. antifungalagents, wetting agents, rheology modifiers, dispersants, anti-freezingagents, driers, thickeners, de-foamers, small additions of toxic solvents, etc.) can potentially lead to problematic consequences when these paints are used to create fine art that is intended to last for decades and centuries rather than a short time in a very hostile environment (i.e. 7-15 years). Some of these additives are known to eventually migrate out of these commercial paints after a certain period of time, industrial products are not recommended as suitable materials for grounds, paint layers, and/or varnish coatings. Additional research is required to assess whether these additives can form potentially deleterious complexes with pigments, create a hazy film on the paint surface, impart brittleness, and/or create a paint film that is more sensitive to solvents. As little is presently known about how these materials will age over extended periods of time, industrial products are not recommended for use. If artists choose to use such products, they are encouraged to record the brand, material, and date of purchase (commercial manufacturers may change their formulation often without notifying the consumer) of the product on the back of the artwork.

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    That very slight acidity should not be an issue. Linen and cotton will get slightly more acidic over time and we should keep in mind that the pH of animal glue (which was for centuries the almost universal size for paintings) ranges in pH from 5.8 – 7.4 depending upon the source.

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    If you don't mind, I'm going to defer to the conservation specialists on whether very slight acidity of PVA could have a destructive effect. ​

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    Many of the rules, including Rule #6, is based on the book Simple Rules for Oil Painting by A. P. Laurie. I was a little confused by it too, but I beleive it refers to building the entire painting in one direction, either dark to light or light to dark, but not in both directions in the layers.

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    It's hard to "reverse-engineer" a technique as individual as this. That said, one point I took from this interview is that the squeegee is very significant, both in achieving the pictorial goal as well as in how the paint film is structured. I remember when I first observed how surprisingly thin the paint was on a Goya, compared to how textural it appeared in reproductions. Modern painters often, I think, don't understand how much subtractive work with a knife was done by earlier artists. If there are any real "lost secrets of the old masters", paint "mechanics" might be among them.

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    It's important to remember that some "rules" of ordering and layering may be based on the assumption that the artist will be using white passages in the first layers to pictorially communicate direct lighting. Not every artist will have that approach, even if it makes good sense in structural terms.

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    The “rules” for painting are only guidelines. Almost all works of the works of the past contain some deviation from rigid best practices. The key is to keep the deviations small. Dark grounds (like the dark red or brown grounds found Spanish and Italian paintings from the 16th c on) are less flexible than white lead and can create major contrast shifts when the superimposed oil paint becomes more transparent over time. This does not mean that all works created on these types of grounds have been disasters. They have all probably altered in contrast in some manner, though. Even the use of a very heavy application of white for highlights means that it will be the mid-tones that darken the most with increased transparency. So it best to use a stable white ground, but fully realize that there are many, many examples where great masters of paining did not.

    Umber and black have a very low pigment-volume-concentration (PVC) when mixed into a usable oil paint and are physically not the best options when used below stiffer and leaner upper layers. However, people have used umberfor underpainting both for its color but also because of its rapid drying due to its manganese component. This is less likely to cause major issues if used in conjunction with large amounts of a paint containing lead white. It is also not likely to cause problems if used as an outline to sketch in the composition. So while it is best practice to underpaint in more opaque high PVC colors, Rembrandt often did the complete opposite. We should realize that his works have altered some over time and, due to their universal esteem and value, are stored/housed in optimal conditions where they are monitored by conservators and other experts.

    Rather than reinvent the wheel, I do think that the guidelines in this article are a good place to start (although #6 is confusing, I believe that they mean light in lower layers and darker in the upper).

    https://www.naturalpigments.com/art-supply-education/simple-rules-oil-painting/

    Again, these should be thought of as general principles that you may need to deviate from in some manner but only in small ways and for specific effects.

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    ​Matthew may have some suggestions but I refer you back to the blog's statement here: "There is undoubtedly an element of chance in the results of this technique"....I think this technique really requires a lot of playing around and testing. I would not attempt to mess with the paint you are using unless you have had a few go's at trying to re-create this method. When you do please report back..we are interested to hear how it goes and might be able to help you troubleshoot.

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    ​If it's sold as wood glue, are you sure it's PVA? If Talens primer is available, I would just use that rather than taking a chance on "off-label" use of construction adhesive.

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    Matthew,

    I think that you covered it well. 

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    ​Thanks Matthew,

    You are a real asset to this forum

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    Tate Conservator Rachel Barker gave a great interview in 2011 on Richter's technique ​that explains some of this: http://www.tate.org.uk/context-comment/blogs/richters-paintings-how-did-he-make-them

    The preparation of his paint is briefly explained- it's apparently strained to remove any solid bits that would interfere with smooth application- but it sounds like it's assumed that the artist leverages knowledge of the drying properties of the colors themselves to avoid problems in layering.

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    The problem with a lot of ad-hoc, hardware store substitutes for bona fide art supplies is that they are formulated with different performance goals, and often include ingredients that would not normally be included in art materials.

    Are the "acrylic primers" you mention sold as architectural coatings, or are they sold as an art supply? ​Your description sounds like they are art supplies, and if so, they would probably be suitable for this purpose, though they probably won't block staining from a hardboard support.

    Of the other materials you mention, Boiled Linseed oil is, in my opinion, the first to tick off the list. Boiled Linseed OIl is not suitable for use in permanent painting because it's not alkali-refined, and because it includes a large amount of catalytic siccatives. You are correct in assuming acrylic would not perform well on top of boiled oil.

    Wallpaper paste is hygroscopic, and remains water-soluble after it dries (though if you've ever had to strip old wallpaper, you might find that hard to believe). When acrylic dispersion painting ground (gesso) is applied over a soluble size, often the result is a crazed priming layer. There are probably more issues the other Moderators can point out.

    Utility-grade PVA adhesive might be OK, but the type sold as a professional-grade art material typically retains neutral color and flexibility long-term, and is more resistant to damage from UV light exposure. If the glue you're considering is recommended safe for use in archival preservation or antique book repair, it might be a good option.


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    I will do the best I can to weigh in on these rather complicated questions:

    1. Yes labeling is and will likely remain vague at best. The specifications regarding media are seldomly ever derived from ACTUAL analytical results. In fact I would say that less than 75% of the time is this ever the case. Labels that state "egg and oil," egg with oil additions," etc., etc. are often just arbitrary assignments based on visual assessments made by a curator (and less commonly by a conservator).

    2. It is often impossible imo to make definitive conclusions regarding binding media based on visual assessment alone. One really needs to have the condition report of the painting in hand and ideally a very thorough analytical report. And even then it can be impossible to know what Botticelli and his workshop truly used. Botticelli's works in particular have likely been restored multiple times over. We could be looking at remnants of unoriginal varnish coatings (as you state) or even unoriginal oil glazes. Or maybe in some cases, we are looking at a passage that might be very well preserved. There are many factors to consider here… 

    3. It is no secret that Botticelli and his workshop pushed tempera to its absolute limit as a medium, producing paintings that rival contemporary works executed in oil that originated north of the Alps. So the Birth of Venus could very well be an example of true tempera grassa. Or the ground may have been carefully prepared in a unique manner. The fact that is in on canvas has and likely always will continue to intrigue. I am not aware of any references citing the traditional mounting of tempera canvas paintings on panel (for great references on the early use of canvas in painting check anything written by Caroline Villers). In fact this would be odd considering the fact that a major reason artists began turning to canvas was because fabric was less expensive than panel, so adding a panel on the back would not be cost effective. But I am not sure cost was an issue for Botticelli. One would have to go digging in the archives for that, in attempt to analyze any extant receipts or written exchanges between the commissioner and his workshop. If this painting has been analyzed recently the results have yet to be published. Yet even if cross-sections are obtained or samples are collected for destructive medium analysis (e.g. GC-MS) I doubt that all of our questions would be adequately answered. It would be wonderful to conduct a technical study of the painting with some top-of-the-line analytical techniques but often funding (as you have already pointed out) is the main hold-up. In Italy this is often the problem combined with a whirlwind of political hoops that one has to jump through in order to carry out a technical study of this magnitude on a painting that may as well be the country's unofficial "banner."

    4. The question about varnishes is tricky. For this particular painting I will go out on a limb and say that it would be impossible to characterize the original nature of the varnish b/c: a) I doubt much (if anything at all) still remains of the original varnish layer b) our instruments are barely able to accurately characterize some of these ancient varnish recipes (e.g. oil-resin) and c) if it was given a layer of egg "wash" at the end it would be difficult to distinguish such a layer from the thin layers of egg tempera paint. But I could be wrong about all of this….I would need to see cross-sections and to be able to examine the painting using all of the criteria I listed in No. 2. That being said there are rare cases where original varnish layers have been identified. If an original varnish is identified it is often very degraded and leaving it on the surface as is is usually not a desirable option from an aesthetic standpoint. What some conservators have opted to do is to leave a small area of the original varnish intact in a place that is not immediately noticeable such as on the outer edges of the composition, possibly hidden by the frame. But most of the time, tempera paintings from the Renaissance possess multiple layers of unoriginal varnish so the concept of removing them from the surface is not one that is hotly contested. I should state that for gold ground tempera paintings it was generally not typical for artists to varnish the surface of the gilded sections. Portions of tooling/incised work may have been given a tinted varnish but even that was not especially common. But today of course many gold ground paintings are completely covered with a varnish layer. Conservators today do take this into consideration when dealing with gold ground paintings. 
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    ​Honestly any up-to-date studies concerning the safety of artists would be in Monona Rossal's publications so I would look there if anywhere.

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    Great questions and I'm really happy you are trying to get more information when you see conflicting results. This is going to be a long answer for a complicated issue.

    You should always use the chemical ID associated with the product you are using, because manufacturers develop SDSs based on their product. This is especially true with things like petroleum distillates which can be any variety of mixtures and naphtha might be one of the best examples of a totally ambiguous term. 

    Having said that, manufacturers are not required to do their own testing and rely on available data to come up with their hazard warnings. In fact, Gamblin's SDS even says, "Specific toxicity tests have not been conducted on this mixture. In accordance with OSHA’s Hazard Communication Standard 1910.1200, this mixture is assumed to have the same health hazards as its significant components." Each manufacturer uses their own algorithm/system to come up with their warnings, so that may be why you see discrepancies between manufacturers depending on which H&S information they include. 

    The unfortunate reality is that health and safety data on MOST chemicals is pretty limited. Section 11 of the SDS will give more specific toxicological information if there is any. But you might see phrases like: "No components of this product above the declaration level of 0.1% have been identified by IARC, OSHA or NTP as carcinogenic." This doesn't mean it's not carcinogenic.There just isn't any data to say that it is. Information from the IARC (International Agency for Research on Cancer), the ACGIH (American Conference of Governmental Industrial Hygienists) and OSHA can give you a much better picture of the current understanding of chemical than the SDS might.

    There are also big differences between European and US standards with European standards tending to be more cautious (if that's the right word). The example you give of a 1B hazard means there is evidence to suggest that the material causes cancer in animals, but not humans. This doesn't mean it does not cause cancer in humans, there just aren't any studies to prove it.There are also no links to the studies that have resulted in that classification. Sources like Toxnet and Pubchem, which provide links to peer-reviewed sources, can be extremely helpful. Were animals fed the material? Was it rubbed on their skin?

    Why does that matter? Because it's important to understand HOW something is a carcinogen. Chemical health hazards are highly dependent on type, dose and route of exposure. Routes of exposure can be inhalation (breathing), absorption (through skin, eyes, etc) and ingestion (eating). How are you exposed to this chemical? If something is carcinogenic from eating it, then your art materials are lower risk because if you're washing your hands and not eating while working, then you're less likely to be ingesting it. However, if it is carcinogenic from breathing it, then you are more at risk standing over a painting, brushing it on and breathing the vapors.

    Asbestos is a good example. It's a well-known carcinogen--if you breathe it in. Mercury is another example. Organic mercury, the kind found in fish, is primarily a health concern when you ingest/eat it, while elemental mercury, the kind found in thermometers, is primarily a health concern if you breathe the vapor. 

    The bottom line is to always err on the side of caution. If there is lack of definitive evidence that something is safe, than always use the highest level of personal protection possible (ventilation, gloves, goggles, etc.). I personally would not be using this stuff with without proper ventilation or a respirator. It's pretty clear that petroleum distillates are central nervous system depressants and can make you nauseous and dizzy and that's enough for me to take precautions, even if it doesn't cause cancer. People safely use these chemicals all the time--they are low risk with proper precautions.

    Some good resources on artist material hazards are:

    Arts, Crafts and Theater Safety: http://www. artscraftstheatersafety.org/

    The Artist's Complete Health & Safety Guide (Book)

    Artist Beware, Updated and Revised: The Hazards in Working with All Art and Craft Materials and the Precautions Every Artist and Craftsperson Should Take (Book)

    Kerith Koss Schrager

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    The SDS will have been prepared by a toxicologist or other credentialed professional as an authoritative reference for health and safety concerns. At Utrecht, when we receive a question about the SDS that we can't answer, we either relay the query to the toxicologist or put the artist in direct contact. I think you should contact the manufacturer of whatever product concerns you and see if more information is available. 

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    ​First of all you should have a long talk with your husband :) This is a very tricky situation and unfortunately if you want to regain that even surface you will just have to remove the varnish from the entire painting. PLEASE realize that the advice we give here is only for you to try as anything you do at this point will risk biting into your paint. What you can do is wear gloves and use a lint-free cotton cloth (e.g. a clipping from a soft jersey T-shirt) that is slightly soaked in OMS. Try to carefully rub the surface in a small area. If you start picking up color then you will just have to wait a month or two longer and try again. If after some time passes and the OMS does not seem to be pulling anything up then you can try to use actual Mineral Spirits to reduce/remove the varnish, always checking to see if you pull up color. One thing: tread carefully where the painting was in contact with the couch as the varnish will be thinnest in this location. 

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    In this scenario, I do believe that the zero-formaldehyde wet-process hardboard is the better option, especially if it is braced for rigidity.

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    ​In any case you might find this previous thread of interest: https://www.artcons.udel.edu/mitra/forums/question?QID=149

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    ​Hi there....we need a bit more information before we can be of service here. First is this your painting? How extensive is the tear? Would you be able to share a photograph?

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    ​Not really in my opinion. Zinc has a unique hardness that, alas, is also part of its Achilles heel. From very early on zinc was used in coatings to lend a harder, and in commercial paints, more scrubbable, dirt resistant, and physically durable film. Particularly as an adjunct to Titanium White. But I am not aware of a comparable pigment that can fill the same roles. Alkyd medium can lend some film hardness, if adding a medium is an option for you. And of course, unless used alone, Titanium White in blends will be influenced by whatever you mix it with.

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    ​With anything that contains zinc white it is ALWAYS best to use a rigid support (with or without canvas attached) as this particular pigment is known increase the level of brittleness of the paint film over time.

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    The off gassing of UF glues is known to tan and embrittle animal glues like those sometimes used as a size or incorporated into genuine gesso or chalk glue grounds.

    There is also mention in the literature that it can also contribute to the degradation of some pigments. This one of the reasons why materials containing it are avoided in museum displays. I do not believe that the concern is necessarily about the structural failure that you are worried about. 

    It is difficult to know if your use of such materials would be a major problem but they should be avoided if possible. If you continue to use these substrates avoid the use of animal glues and make sure that your panel is well sized/sealed before applying your ground and paint layers

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    ​The form of zinc that is a concern is zinc oxide, because of its reactivity with fatty acids, but zinc in and by itself is not necessarily bad and you always need to be aware of its form and how it is occuring. For example, zinc sulfide is considered nonreactive and not associated with soap formation, while zinc is also used to modify other metallic crystals in order to create a specific color. The most common one you might be aware of is cadmium zinc sulfide, where the zinc is imbedded into the structure of the cadmium sulfide crystal to produce various shades of yellow. In the case of PBr33, the zinc is modifying the iron chromite and in the process produces various shade of brown but the resulting crystal is considered a stable formation and does not present the same issues as zinc oxide on its own.

    Hope that helps.

    Sarah Sands
    Senior Technical; Specialist
    Golden Artist Colors

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    Sizing reduces panel absorbency, preventing excess uptake of the paint/oil primer vehicle while providing a uniform surface for adhesion with the ground. Our recommendation at Utrecht has always been to size hardboard prior to oil priming, originally with RSG, currently with Acrylic Sizing or a similar synthetic product.  Although wood doesn't suffer the same destructive effects as canvas when oil paint is applied directly, that type of support does tend to wick away the paint vehicle, leaving a weak, underbound layer. We believe it's better to isolate the board to preserve the full strength of the paint and oil primer. 

    One reason some artists prefer not to size wood and hardboard before oil priming is because wet acrylic size swells the fibers and raises what some feel is an undesirable texture. I have heard some artists "seal" panels with alkyd painting medium prior to alkyd-priming, which sounds reasonable. I would not, however, advise using alkyd under our Oil Priming White.​

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    ​As you probably already read in our "Rigid Supports" document in the Resources section we generally do not recommend adhering completed paintings on canvas to rigid supports. This is partially because we have not tested every single art material out there using this procedure. However, it sounds like you are not painting use lots of texture/impasto (YES the heat press WOULD crush the impasto!) which helps you to avoid most problems that could come up using the materials you have listed. In short, we do not think your paintings will suffer down the road. As for sizing the rigid support first it couldn't hurt to do so. And if you do this with liquid BEVA the bond with the BEVA film will be even better.

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    ​As to the question of Oil Size, preparation is paramount when one considers the amount of time that goes into a gilded work, whether Frame or Icon, what is important is allowing the proper drying time for the materials; for example, the temperature and drying will always vary depending on the humidity in a room. I try to gild on low humidity days and specially in the summer the room should be in the low 70’s with very low humidity. If we are working with Oil size as to Water Gilding, I use Rolco or Kemp Burnish Sealer which is a primer/sealer as to Shellac and after 2 to 3 coats directly over the wood or real gesso, not latex, it really hides many imperfections in the wooden surface. The Burnish Sealer comes in a few colors (Red, Ochre & Gray), and after 24 hours I then apply my size. I use many different brands from Kurz-Hastings or Rolco Quick Size, this always depends on the size of the project and the working time needed, obviously a large project will require a greater working time. The wonderful quality of Burnish Sealer is the final product after the gilding and with minimal rubbing the burnished finish is quite nice and can receive a Casein Patina if desired and then a final Rolco Acrylic Top Coat or Ronan Clear Overcoat Varnish. Obviously I stated a few manufactures of various materials but all Gilding Suppliers have their individual companies they represent, so if you cannot get something from one company another’s product is just as good, for example I also use LeFranc & Bourgeois products from Charbonnel.
    Martin Kotler

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    ​Koo is ertainly correct about the fact that there mordants  that can be applied in an aqueous system. There generally dispersions based on acrylic resins which dry water resistant. I understand from your post on another formus that you were interested in sizings for oil mordants.

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    I understand from another forum that you are asking for a material to cut the absorbency of the gessoed panel before the application of a gilding oil mordant. I know many gilders who apply shellac and let it dry before applying oil mordants to absorbent surfaces. This is probably the most common practice today. The use of shellac in fine art does not go back that many centuries, though. I have also used applications of egg water and even glair to cut the absorbency of gesso and sections of egg tempera when I have added fine gilded details to an egg tempera reconstruction. I would bet that an initial “size” coat of oil mordant would also work but I would want to make sure that it thin enough that you worked quickly and make sure that you did not get textural overlaps. I would guess that shellac would be the most common material for this. We have contacted a few others who will likely have something to add.  

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    ​I had planned to add my own experience and thoughts on this but you two have it well covered. Thanks

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    ​Sarah makes a very important point about variations in pigment that can't be predicted by "recipe" alone. Even in paint manufacture where a proprietary formula is used, each batch of pigment is tested by hand by making what is essentially a small amount of paint.

    In addition to Sarah's advice to examine the paint body after it rests, I would add that it's not always good to try making the stiffest paste possible. The paint vehicle has an important optical function in bringing the color to its best advantage, something that only works when clusters are reduced and each particle is enveloped in oil. Some pigments can be used in fairly high proportion to vehicle (Dutch Boy White Lead was 88-89% pigment) but a dense  putty that releases from the slab is not only underbound, it also makes movement of the muller impossible.

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    ​As Matthew said, the feel on the slab is ultimately the best guide and part of the art of grinding your own paint is gaining experience through trial and error. I would caution against using oil absorption rates that you can find published. They invariably come as ranges which will not tell you about your specific pigment. And to be honest, how even oil absorption rates are calculated is weighing how much oil you need to add to 100 grams of pigment until it is a stiff spreadable paste. So, your right back to that sense of feel. And we would encourage you as well to read the article Matthew points to as it should put some of these issues in context and also point to a common misconception between oil absorption rates in terms of weight versus volume. Lastly, understand that paints can feel different after they are allowed to rest for a period after mulling as the oil will continue to wet out the pigment and the paint can sometimes stiffen or loosen up as a result.

    Anyway, making your own paint is a great way to learn and explore the nature of pigments. Keep accurate notes and if you can get a accurate digital scale it will be easier to know how you can repeat something  that you like.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    Also, I really like Martin's suggestion to explore screen printing mesh.

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    One additional suggestion: If oil paint sticks are the final choice of medium, replace the poppy oil used for wetting with a low-viscosity alkyd medium. Poppy oil is known to yield a less flexible film than linseed, and I think flexibility and tensile strength of the dry film will be important here.

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    Are you asking in reference to small-batch, handmade oil paints? If that is the case​, consistency on the slab is a very good indicator of optimal proportion. Just watch the product develop, and gradually add oil to the pigment until a nice, workable paste is achieved.  Regarding published ratios, Golden included average absorbency for common colors in a great "Just Paint" article last year: http://www.justpaint.org/volume-weight-and-pigment-to-oil-ratios/

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    1. Do you think one would be better than the other (pros/cons)? Honestly it sounds like you should go for working with silkscreen as you are after a bleed-through effect anyhow. I cannot see how one would be "better" than the other in terms of longevity, they are simply different but others may weigh in on this with additional info.

    2. Would artist polyester also handle extreme solvents?
    What do you mean by extreme? I cannot see why you would need something else other than mineral spirits. So yes you should be fine with that.

    3. Would oil work vs. ink on silkscreen?
    I do not see why not? As we have never tried this personally we would encourage you to experiment and please report back on your experience :)

    4. Silksreen would be difficult to staple onto a stretcher correct? No. In fact this is how it is often prepared when used in the traditional sense.

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    The silkscreen industry designs and uses a variety of Polyester materials according to the needed images to be screen printed or by the (Mesh) required for the printing. You might look into silkscreen polyester as a source as it is designed to last under extreme solvents; e.g. Xylene, Acetone, Mineral Spirits, etc. Just a thought

    Martin Kotler 

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    ​So to begin we do not think this has anything to do with the aluminum support or the materials/techniques you are using. It is indeed strange looking and still a bit impossible to diagnosis without examining the surface in person so we will do our best to try and give you some advice here...
    1) It could be fatty acid effluorescence but I am leaning towards not. The primary reason being that I have never seen FA effluorescence that appears in such distinct circular patterns. To deal with this problem one can use a soft brush and/or a bit of OMS to wipe the stuff away and certainly varnishing will help if that does not fix the problem.
    2) This might be some sort of additive from one of the packaging materials that got deposited on the painting (thinking along the lines of PVC or something?). It is harder to advise on how to deal with this as it will entirely depend on the additive. Have you tried taking OMS to the surface? What does it do? Varnishing may or may not help but you also might risk locking in whatever additive you are dealing with....which again may or may not be a big deal.
    3) This could be mold....hard to tell. You can look up instructions on how best to deal with mold on paintings in our Resources section (there is a mold abatement document). Even if it is not mold it cannot hurt to treat the surface as if it were affected by a mold outbreak. After that then yes I probably would seal the surface with varnish. 
    I am sorry we cannot offer a more definitive answer...please let us know if you find out anything.


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    ​​I agree with the answers already given by Kristin, Matt, & Brian and have nothing new to add regarding oil paint on on unsized fabric. But I do have one suggestion, which is to try painting on a lightweight metal screen and let the paint go through that. You do mention needing to wet the support to extend drying time. But keep in mind that the various brands of oil stick have different consistencies and different drying rates, so you may want to research that.

    Richard Frumess

    R&F Handmade Paints

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    ​Is there any way for you to post a picture of the problem?


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    I'm wondering if the discoloration was the result of a reaction between the white pigment and something in the packing materials. ​What sort of "foam" was used to wrap the artwork?

    Regarding the preparation of an aluminum panel for acrylic dispersion painting ground, I recall Gottsegen recommended finely graining the support with steel wool followed with a thorough cleaning with denatured alcohol, to ensure optimal adhesion. I don't remember any issue with discoloration from aluminum panel, however.

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    ​I have sent a note to R & F about this thread and hope to hear a response about some of the issues mentioned here. I have other comments about your latest post but will wait until we have heard from perople with expertise in oil sticks.

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    Sorry for the belated response. I was away for a couple of days. I will reach out to one of our moderators more experience with oil sticks to weigh in on this.

    As to my thoughts, I need to sort of separate my role as a conservator from that of a moderator here. As a conservator, I need to approach all paintings as the artist intended and honor their choice of materials as a component of their aesthetic and process. This is different from the goal here, which is to offer as much information about the options available to arm the artist with the knowledge to make informed decisions on their materials choice and methods beforehand.

     So with that stated, I have to agree with Matthew on all of the points that he raises. Supports generally perform best when they either possess inherent rigidity that is greater than that of all layers that will be added (you do need to take into account the aging properties of the added layers…will they become more brittle with time?) OR supports that are made rigid through the application(s) of size and/or ground layers.

    Your process sort of sidesteps these criteria. The open weave and extremely insubstantial nature of muslin is unlikely to adequately support the oil stick application as it ages. Your lack of ground means that the fabric is not made more rigid that in its untreated form.

    The above also ignores the issue of oil absorption into the cellulose fabric. We have written about this on MITRA in the past. There is some danger of this rotting the fabric overtime. The lack of oil staining may mitigate this potential problem but it does not mitigate the issues above.

    So, taking Matthews comments and these into account, it would probably be best to either use a artist polyester fabric if you continue to use oil sticks or to switch to acrylic dispersion paints if you want to continue to use muslin. Unfortunately, due to the way in which acrylic dispersion paint dries, they are unlikely to be made into a stick form.  

    To come back to my first point, we at MITRA hope that our users will take the current info about materials and processes into account to make your work as permanent as possible, but also understand that artists will sometimes deviate from best practices in pursuit of their vision. With this in mind, we also hope that we can offer alternate methods which may allow you to create the same effects but with more archival materials.

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    Regarding consumer products containing phenolic resin: it looks like it's still used in a few nautical oil-based varnishes ("spar varnish") ​including Pettit Easypoxy Hi-Build Varnish 2056

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    This may help. From "House Paints, 1900-1960: History and Use" By Harriet A. L. Standeven (2011 , isbn 978-1606060674) from the section "ARTISTIC USE OF COMMERCIAL PAINTS":

    There is thus far no evidence of artists using household paints based on phenol-formaldehyde resins, although the resin has been found on works of art. Phenol-formaldehyde was certainly used by Rothko for his Seagram murals... and was detected on the murals in the Tate's collection. Although the source of phenol-formaldehyde in this instance is unclear, it is likely to have originated from a printing ink. Phenol-formaldehyde was widely used for this application in the late 1950s, and the almost ubiquitous presence of lithol red (PR:49) on the Seagram murals (Carlyle et al. 2008), a pigment commonly used for printing, suggests Rothko may have obtained his materials from the printing industry.

    A second notable occurrence of the presence of phenol-formaldehyde is in the faked Vermeer paintings executed by Hans van Meegeren in the 1930s. In this instance, its detection provided incontrovertible proof that the paintings were indeed faked. In this instance, Van Meegeren chose phenol-formaldehyde, as it enabled him to re-create the visual effect of a cracked seventeenth-century paint film. He bought the resin as a thick solution in benzene or alcohol, which he diluted with the essential oils of lavender or lilac. He then pigmented the resin and heat-hardened the finished painting for four to six hours at temperatures of 120 to 130 degrees C to create the craquelure that is characteristic of aged paint (Breek and Froentjes 1975).​

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    Thanks for the additional detail. It sounds like you are selecting a light, po​rous fabric to deliberately induce strike-through of the paint. I would expect cotton muslin to become saturated with the oil paint vehicle, which can have a destructive effect on the fabric. There is a precedent for painting on thin muslin, in historical stage scenery backdrops, but obviously those would not have been expected to have survived into antique age (and I believe casein was often the medium used, for fast rate of drying and matte finish).

    Another issue with the application of oil paint (even in stick form) to an unprotected, absorbent support is that enough of the paint binder can be taken up by the support material to leave the paint layer under-bound. 

    In my opinion, the most significant challenge with the approach you describe is the vulnerability of the aging paint film on a support material that may not resist deformation from gravity and other forces that will cause the paint to move and flex. Canvas that is considered heavy enough for use as a painting support would not normally be thin and porous, because it needs to provide a flat plane with minimal movement. Based on these factors, I think this project would be better suited to acrylic paint, a medium that will maintain strength and flexibility for a long time. 

    I would be interested to hear from the Moderators who are qualified to speak to conservation issues- I would expect a thin, porous painting with color on the verso would present unique conservation challenges.

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    Without applying something to isolate the fabric from the paint, I don't think cotton muslin is a good choice for this approach, if durable results are the goal. Since polyester artist's canvas is not susceptible to the destructive effects of direct contact with drying oil, and since you mention you are already using both poly and muslin, synthetic seems the better choice. I would recommend using a bona fide artist's canvas rather than something from the fabric store, which may have surface treatments, unstable colorants and optical brighteners. 

    I would also be interested to know the planned display/installation method. Will the fabric be stretched, mounted to panel or suspended freely? That will be important as well.

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    ​Are you finding that you are getting oil stains around areas of paint? Or can you not tell because you are covering the entire canvas with oil paint?

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    ​Oh! Is the painting painted ON the tar paper? The tar paper being the substrate? Is there a ground at all?

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    ​Yes indeed Matthew...and thank you. I believe we do recommend to use gloss over matte in our document but if not thanks for stating that...I will check and amend it just in case we have neglected to include this.

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    In our line of acrylic dispersion gel mediums, gloss performs better than matte as an adhesive for mounting fabric to ​panel. I think this is probably the same with other brands. For prepping canvas to receive oil primer, while thinning a painting medium does work, there are low-viscosity acrylic mediums and ready-to-use acrylic sizings that can be applied full-strength without thinning. We offer one, I believe Golden has several, and there are probably others I haven't tried yet.

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    ​​We try to avoid promoting any one single brand but if you buy a higher quality acrylic dispersion medium from a notable brand (so not the cheaper stuff) you should be fine.
    And yes...the medium is different than gesso (which has fillers). There are instructions for how to attach fabric to a rigid support in our "Rigid Supports" document in the Resources section if you need more information.

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    That should work fine and create a rather stable painting substrate. You can follow the procedure outlined in our “Rigid Supports” downloadable pdf in our resources section; https://www.artcons.udel.edu/mitra/resources for the procedure. I would use acrylic dispersion gel medium if avoiding BEVA 371 rather than PVA dispersion so as to not add an additional resin to the composite.  The “gesso” in the Gessoboard is already bound in an acrylic dispersion so why add another material to complicate the situation.

    I would probably size the linen with a thinned fluid acrylic dispersion medium rather than animal glue to avoid the reactivity of the glue, to keep the materials list as short as possible, and prevent any diminished adhesion between the glue size and any acrylic dispersion that soaked through to the surface of the linen.

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    ​Well as you probably know we would not recommend using such a product if you are interested in long-term preservation of your work....but if you are well aware of this and are more interested in the aesthetic qualities of tar paper than we cannot argue against that :)
    While we do not have experience working with this material we would recommend trying BEVA 371 adhesive. Be sure to use protection when applying the stuff (e.g. respirator, ventilated space, etc.). And you may witness a slight shift in gloss/sheen of the paper after applying the adhesive so you might want to do some tests first.

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    ​Black oil contains lead so YES protection is highly recommended! Remember that inhalation of any type of fine, particulate material is possible when sanding/scraping and that a dust mask should be worn during this process. You can always use a damp rag at the end to clean off any residual "dust" that remains on the surface and dispose of that accordingly. If you are unsure of how to properly dispose of lead-contaminated material check out our Health and Safety document in the Resources section.

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    ​Koo, you are correct as to the relevence to plywood as well. We hope to hear from someone very well versed in these issues rather than postulating ourselves.

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    ​At this point we have an inquiry into a couple of our moderators who are more knowledgable about these products....so hang tight. There will be a detailed response come Monday.

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    Hi

    Good points and questions. There is evidence of the deterioration of urea-formaldehyde adhesives which release harmful vapors.

    First, you can purchase zero formaldehyde MDF. This quality is used for museum displays where issues of off gassing are paramount. Hardboards can also be purchased with no formaldehyde component.  I find neither MDF nor hardboard perfect due to other physical properties but that is another issue. I do not believe that the deterioration of PVA is a major concern but if you want to be extra careful, use a diluted high quality acrylic dispersion or even an acrylic solution (eg B-72 in acetone/ethanol) as a size. Others may have additional thoughts on this matter.

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    Most modern oil paints exhibit short pseudoplastic flow (described as short, buttery paint) due not only to the homogeneous particle size and shape of pigments, but also to additives typically used in these paints.

    Oil paints made from pigments of heterogenous particle size and size exhibit different types of viscoelastic flow. At Natural Pigments we have measured a wide variety of pant behavior, including viscoelastic; time-dependent viscosities, such as rheopectic (viscosity increases with duration of stress) and thixotropic (viscosity decreases with duration of stress); and non-Newtonian viscoelastic flows, such as shear thickening (dilatant) (viscosity increases with increased stress) and shear thinning (pseudoplastic) (viscosity decreases with increased stress). Chemical and physical interactions between pigments and drying oil gives rise to incredibly complex and often surprising behavior. Although additives are used in very small amounts in professional-grade oil paint—usually less than 2% by weight of the pigment—their effect on flow is dramatic since the additives are adsorbed to the surfaces of pigment particles.

    Bodied (partially polymerized) drying oils impart long flowing behavior to paint that is also described as “sticky” or “tacky”. This is due to the large molecular weight of polymers. Adding bodied oil to oil paint can often accomplish what you are seeking. Grinding barite (barium sulfate) in a blend of bodied oil and refined oil and then adding this mixture to your paint is also useful and also does not thin the paint.

    Basic lead carbonate (lead white) in drying oils with low or no free fatty acid creates long, ropey paint. Oils with free fatty acid, especially above an acid value of 4 or 5, create the opposite. We have found highly variable paint flow from lead white made according to the stack process or “old Dutch method”. These paints exhibit different flows depending on the particle size and crystalline forms of the pigment.

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    ​Also, Matthew, thaks for the tubing primer.

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    There is ample evidence that Dutch process stack lead white paint behaves in its very characteristic manner due to the diverse, heterogeneous morphology (as well as larger size) of the pigment particles as well as its chemical reactivity with the oil medium. I know of two (periodically, three) manufacturers who make old style lead white. It is interesting to experiment with these but you may certainly find a paint that affords you the tactile and physical effects you are looking for without resorting to such rarified materials; and I mean no disrespect to those materials, I have stockpiled a substantial stash of them just in case these manufactures stop production.

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    Thanks, Brian. http://images.utrechtart.com/Content/pdf/experts_archive/studiocraft/Long_Bodied_Oil_Paint.pdf

    Also, for artists reading this who don't yet know how to manually fill paint tubes, this is very useful when working in batches: http://images.utrechtart.com/Content/pdf/experts_archive/studiocraft/tubing_mixtures.pdf

    In addition to the widespread use of stabilizers/amendments,  I think the very small, uniform particle size of modern, precipitated pigments may also have something to do with the texture of today's factory-made whites, compared to what is seen on historical paintings. (Other Moderators will likely know more about this than I do.)

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    Matthew, you are welcome to post the link.

    As to the question. The answer really depends on what paint you are attempting to modify and exactly what handling properties you are searching for. Most commercially available paints have added enough modifier (aluminum stearate, castor wax, aluminum hydrate) to create a short buttery paint that is similar in feel across the paint range. When modifying these you need to add enough of the material (and likely extra oil) to surmount the action of the original modifier. Matthew’s suggestion may work for what you want. I have made handground lead white oil paint that was extremely ropey by admixing some barium sulfate and a bit of extra linseed oil into the paint while I was mulling it. The consistency was both dense and ropey at the same time.

    If it were me, I would probably mull up a number of additives in oil to a loose constancy and experiment with each of these by adding them to my white to determine which created a paint with the rheological properties that most closely resembled what I was searching for.

    Please report back and let us know what worked for you.

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    ​You might get close to the results you describe by adding 10% by volume marble dust and some stand oil to factory-made titanium white. Blend on a glass slab until homogeneous, work with a glass muller, then introduce  a small amount of stand oil with the knife. The resulting mixture will be long and ropy with distinct ribbons. (There is a PDF instructional on the Utrecht site with pictures. If the other Moderators don't object, I'll link it in a subsequent reply. There are no product links in the document.)

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    Moistening the acrylic ground before painting can help improve brush movement and reduce "breaking". It doesn't have to be sopping wet, just enough so the ground doesn't absorb all the water from the paint. 

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    ​Also. I know that you know this but it would be best to really try to minimize the use of retarder. A quick search of "retarder" on MITRA will reiterate some of the dangers of using too much retarder when painting with acrylic dispersion paints.

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    ​Thanks Matthew,

    We agree with your assessment.

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    Do you see some color lifting with unmodified paint, or just when you add retarder? Do some colors seem more prone to lifting than others? If you are not exceeding the recommended proportion of retarder by a huge amount, you may be able to ​improve things by adding acrylic medium and retarder at the same time, instead of retarder alone. In cases where paint seems to have formed a normal film but just feels tacky, your notion to top-coat with additional medium sounds to me like a good fix. If the paint stays very soft for a long time, however, it might be better to scrape it off and try again without so much retarder.

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    Of course this is a complicated question...and it depends on which solvent(s) we are talking about but in general, yes, solvents can and may affect the underlying acrylic layer. We do think that having the oil binder present on top and throughout will provide a sort of "buffer" but this would need to be tested to confirm our theory. Oil paint applied on top of a traditional gesso ground will, for example, drastically reduce the ground's sensitivity to water applied to the surface...but not completely. Anyhow one way you can mitigate potential problems in the future regarding this issue is to use varnish coatings that remain soluble in low aromatic mineral spirits which acrylic dispersion paints/grounds do not tend to be sensitive to (e.g. Regalrez, Golden MSA).

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    ​Thanks for the update Koo...

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    ​Hi there...yes it should be fine to use this fabric if you are mounting to a rigid support.

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    ​Yes this has been our experience with the film...very glad to hear it is working better!

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    While I do not know with absolutely certainty, I suspect that hydrogen sulfide (that rotten egg smell) evolves from by a liver of sulfur solution.  Hydrogen sulfide is a common ingredient in air pollution.  As an oxidizing agent, it is corrosive – which is why it tarnishes the silver in metalpoint drawings and darkens lead white pigments (now prohibited for artist's use).  Conservators see darkened lead white (lead carbonate converted into lead sulfide, usually resulting from exposure to air pollution or the VOCs emitted from plywood) pigments quite often in old master "heightened" drawings, in illuminated manuscripts, and, also, around the edges of the preparatory grounds for metalpoint drawings. However, oxidizing agents also attack the double bonds of cellulose, accelerating the symptoms of paper aging, such as brittleness and yellowing.  As a paper conservator, I cannot recommend the exposure of paper to hydrogen sulfide.  At the same time, we do not know how much exposure to hydrogen sulfide (how long, what concentration) is required before meaningful (greater or faster than "normal") degradation takes place. So a pragmatic approach would be to expose the drawing until you get the results you want and use a good quality, sufficiently sturdy, and toothy paper as the support for the preparatory ground.  

    As to why whiskey breath would accelerate tarnishing of silver, I cannot say – must have been something he ate!

    - Margaret Holbein Ellis

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    ​There is so much to think about, here. I don’t know whether Ag2O looks different that Ag2S, but I think that sulphur is never a good idea.  I wonder whether the Ag2S would be stable, or could continue to react, with atmospheric gases. I think that the sulphur would be bad for the paper, and may react with the acrylic, in either sheet or dispersion. Ultimately, I think that keeping thing as chemically simple as possible is always the best path to stability. If enhanced oxidation is really needed, I would be least uneasy with exposure to H202, since it brings only H and O, to the party, but it would have to be in a gaseous form, for my comfort, and I have no ideas whether this might work. Blowing on the image would bring it CO2 and any biologicals that might be expectorated, with the blows, and I would imagine that all would probably be a source of oxidation. 

    Hugh Phibbs

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    ​Hi Koo, I don't believe that short-term exposure to liver of sulphur (a varying mixture of potassium sulphides) would necessarily cause any detrimental effects to a paper-based support; in fact, liver of sulphur was used to tone black and white photographic prints around the turn of the 20th century.  Due to the fact that this substance is alkaline, I also don't think that short exposure would be problematic for an acrylic ground.  I'm not sure how it might affect a wood-based panel support - perhaps someone else could weigh in on that one. 

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    As a working oil painter and someone with an interest in colour theory and colour matching, I have a couple of suggestions. Firstly I should say that almost all my experience is with oil, not oil-based alkyds, so someone else might have to address colour changes in that context. If you are touching up sections of an oil painting, it helps to know which medium was used in the original painting – best to use that as a base, if you can. If you do not know, more general criteria might apply, e.g. higher gloss and smoothness might point to the use of bodied/ stand oil in the original medium. To start matching colour, I'd suggest first oiling out the section you are touching up, and a little bit beyond (see elsewhere on MITRA for more information on oiling out. Basically apply a very thin layer of oil with a fine brush, then wipe to make the layer even thinner – just the barest minimum to get a "wet" appearance). To match the colour itself, decide whether you want to use a more transparent or a more opaque palette – let the translucency of the existing section guide you. Often you might find darker passages are more translucent and lighter ones more opaque. To select the best paints from the palette for your match can indeed take much practice, but there is a more "robotic" method similar to an approach apparently previously taught by Frank Reilly at the Art Students League (and explained to me by Dr David Briggs). Essentially it approaches the target colour by first matching value, then hue and finally chroma:

    - Select two paints that "bracket" the target colour in hue (e.g. a blue-green can be bracketed by a blue and a green, an orange by a warm yellow and warm red, and so on)

    - Tint or shade both paints till they are both roughly the same value as the target colour (e.g. if you are matching a light blue-green you might have to add white to both the blue and the green till they both match the target in value). With shading you have to be careful; you can use typical carbon-based blacks to shade cool colours but might have to use (raw or burnt) umbers to shade e.g. yellows. Both tinting and shading can change hue significantly, so at this stage you might find that you need to change one or both of the bracketing pair and start again.

    - Next use the (tinted or shaded) bracketing colours of the same value as the target to create a mix that matches the hue of the target – start with the one already closest to the target in hue and add the other incrementally.

    - If the target has very high chroma and you have chosen that highest chroma paints for matching and still can't match it, you are out of luck – no match possible! However if the chroma of the target is lower, you next lower the chroma of your paint by mixing it with a neutral gray.

    - The neutral gray should be slightly higher value than the target, if only because adding it to your mix inevitably lowers the value somewhat. Add incremental amounts of the neutral gray to your mix until the colour match is very good. To mix a good neutral is a separate topic; some manufacturers offer a range of neutral grays at various Munsell values, else you can mix your own with any white, a typical bluish black and e.g. a small amount of burnt umber to counteract the bluishness of the black.

    - Some final very small adjustments might be necessary, e.g. correcting value by adding a small amount of white or correcting a drift in hue by adding small amount of the bracketing (equal value) paints.

     

    You can test the colour match along the way by holding a paint mixing knife up to the section you are in-painting, or painting onto e.g. a piece of non-absorbant paper and doing the same comparison by eye or – esp. as you start getting really close – by simply painting in! If the colour does not match well, you can wipe it away; one of the pleasures of oil painting. This works best on very smooth surfaces; on a textured surface there is more risk of the "wrong" mix getting stuck in "valleys", which you then need to remove with solvent etc  - just don't go there – rather stick with matching by eye some distance from the painting surface.

    Hope this helps!


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    I am happy to say that you can set aside your worries regarding loose weave canvas supports (also called "open" weave) IF you are mounting them to a rigid support. So paint away!

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    I cannot answer all of these points but will weigh in on what I can and send the others on to others. First as to terminology, my resources say one word: metalpoint. As to your question about the use of whiskey to speed up oxidation. I do not believe that this would have any real contribution. The ethanol portion would be reactive to the metal than plain water. I do not believe that any components in the oak casks associated with aging the Whiskey would reach the metal but I guess that perhaps the tannins could theoretically have a tiny effect, but I doubt it. Others may have opinions that are more concrete on this. I hope that some of our paper conservators and scientists can comment on your other points.

    BTW, you would probably have interest in this recent publication.

    https://www.archetype.co.uk/publication-details.php?id=239

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    ​Thanks for your insight Matthew!

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    ​Speaking in terms of what the artist might do in-studio to re-enter an in-progress or recently finished picture, the medium used in the initial work can have a significant influence on the degree of color change from wet paint to dry. A medium that helps preserve the wet appearance of colors makes it a lot easier to resume work on a dry layer. (Usually gloss mediums are better in this regard, especially ones that dry with a 'candy' finish.) Taking this approach can often eliminate the need to re-wet the picture ('oiling out').

    My recommendation for sharpening the skill of mixing and matching color would be study of the Munsell color system, with color chips. Use whatever type of paint you like to duplicate the chips, alone first, then juxtaposed against neutrals and contrasting colors. (If you really want to 'feel the burn', use gouache.) A few weeks of this and you'll be on your way to developing "perfect pitch" with color.

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    Honestly if you ask five conservators how they might retouch a painting you might easily get five different answers. However one thing will always remain the same: the colors/paints that trained conservators use are stable and readily reversible. So not only will our color palette most likely differ from an artists palette, our medium tends to differ as well. We choose paints that are chemically different from the original paint (e.g we might use urea aldehyde paints on an oil painting but NEVER oil paints on an oil painting)....and I am not sure you would WANT to touch up your painting with paints that are readily reversible! Should your painting need cleaning or even re-varnishing in the future, all of the "touched up" areas would be at risk of partial or complete removal. So we do not use oils or alkyd paints to retouch artworks b/c a) they will change in their appearance over time and b) they are not readily reversible.

    As for color matching....you have already cited one of the major challenges that conservators often face when dealing with retouching. And sadly there is no smoking gun here...it takes years of practice and patience to be able to balance hue, chroma, gloss/matte, and even texture. There have been some instances when conservators turn to science, using something like a colorimeter to obtain numerical data of a colored passage on a painting to help inform them when choosing a particular mixture of pigments. But unless you have one handy this is not especially feasible. There is a document on my academia page that you are more than welcome to take a look at. It lists the relevant optical properties for specific pigments that conservators often use for inpainting.

    I am sorry that we cannot be more helpful in this instance...but we will reach out to some of our color specialists on the board to see if they have any additional information that might be useful!


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    ​Great question....we have recently responded to two similar inquiries which we encourage you to read here and here. Let us know if you have additional questions after reading through these two threads...

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    ​Most of the Kilz water-borne products are made using styrenated acrylic copolymer, not 100% acrylic dispersion base. In architectural coatings, this is usually for sake of economy, as the generally better performing 100% acrylic is more costly. Also, house paints are made using plasticizers and coalescents that would not normally be used in artists' painting grounds. 

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    We have to be honest here and say that we have no idea if this is a material that would be considered permanent as a sealer/sizing coat. It may be great, but it is neither made, nor tested for this purpose. I would stick with GAC 100 or 400 to be safe. I would personally use GAC 400 on panels, as it is less gummy and more rigid.

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    ​While BEVA film can be a wonderful product, we have experienced "good and bad" moments with the stuff and are not always sure why this occurs (possibly each batch that is prepared is slightly different). We have found that BEVA film is most successful when used in multiples or together with liquid BEVA. I am including instructions that we have in our "Rigid Supports" document in the Resources section that you might find useful:

    Apply one to two even coats of dilute BEVA adhesive (thin cream consistency) to the panel after cleaning the surface and two coats to the reverse of the canvas (wear adequate protection as solvents are required). If you are using BEVA film it is better to use two sheets of film as opposed to one, although one sheet may be able to provide enough adhesion. Place the film with the BEVA-side facing the panel (or canvas if you are using two sheets) without removing the silicone-coated Mylar and apply heat evenly using an iron (BEVA adhesive requires a temperature of around 65.6 degrees Celsius to be re-activated). Weight down the surface until the BEVA has cooled and then carefully peel away the silicone-coated Mylar (NOTE: If you attempt to remove the Mylar too soon you will pull up the BEVA). If you are using two sheets, repeat this process with the other sheet of BEVA film when applying to the reverse of the canvas support (consider placing silicone-release paper/Mylar beneath the canvas when applying heat, silicone side facing up). Then position your canvas directly atop the BEVA film, place silicone-release paper/Mylar (silicone side facing down) atop the canvas, and apply heat. If you are using BEVA adhesive simply wait for the coats of BEVA to dry (in a well ventilated space) and repeat the aforementioned step. If you experience difficulties using BEVA film try applying a coat of adhesive to the back of the canvas or switch to the adhesive altogether.


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    ​Hi -

    Just a quick correction on something you said:

    "...regular Shellac can dissolve acrylic paint due to alkaline sensitivity to ammonia but Shellac BIN seems to be ok"Actually, as the following articles point out, it is actually the reverse that is true - with some acrylic products dissolving shellac-based ones due to shellac's alkaline sensitivity:

    Waterproof India Inks and Shellac-based Primers

    OPEN Acrylics, Shellac, and SID

    With acrylics, there is some alchohol sensitivity, so putting BIN on top of acrylics would likely bite into them some. But not because of any ammonia sensitivity - that you have a bit backwards.

    Hope that helps!

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    ​Hi -

    I passed your question onto Mike Townsend, who has done the most testing and application research on pours and cell formation on our technical team. Below is his reply:

    Poured paint applications are currently quite popular.  GOLDEN recently published a JustPaint.org article to help get artists off to a good start, located here: http://www.justpaint.org/understanding-the-techniques-of-pouring-acrylics/ . You should be able to use various paints and mediums for this technique, but there are some important factors at play when trying to achieve cellular patterns.

    Our main testing focus for creating cells has been to add isopropyl alcohol. Cell patterns are produced by blending low density-pigmented paints with low density additives (Isopropyl Alcohol) in the lower layers, which in turn push through paints with a higher density, forcing them apart. Alcohol wants to readily escape the paint mixture and it takes the paints it is mixed with for a ride to the pour surface. This is of course assuming the paints are thin enough to allow for the rapid movement but not so thin that the developing patterns break down before the paint is able to dry. While there are other forces at play here, this is the idea behind the process. If the isopropyl alcohol is an issue for your sensitivity to various solvents, you may need to try other forms of alcohol or another additive altogether. There are concerns that the use of silicone oil in a paint mixture can cause poor film-formation in the acrylics, and also poor intercoat adhesion for any paints, mediums or topcoats/varnishes applied over them. Therefore, we cannot endorse the use of silicone in artwork that you hope will last the test of time. Maybe it will be okay, maybe not. We just don't know. The same reasoning goes with the use of a torch to coax the patterns to develop. We don't know what it being released into the air, or if the heat is great enough to alter the film formation process. Heat and/or flame with highly flammable isopropyl alcohol is a very dangerous combination, so please do not do this.


    We hope that helps!

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    ​No...the use of RSG does not necessarily mean that a painting WILL crack. This is further mitigated when a canvas painting is adhered to a rigid support. When dealing with RSG the main culprit responsible for cracking is changes in the relative humidity and temperature. If you use RSG, either as a size or to adhere your canvas to a panel, and keep your artwork in a stable environment then there it is far less likely that cracking will occur. But adhesives such as acrylic and neutral-pH PVA adhesives will not respond to changes in the environment (well nowhere near as readily) which is why we advise using these materials as sizes. BEVA 371 also works well as an adhesive for adhering canvas to panels.

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    ​We would not advise going this route however we are also not 100% positive that it wouldnt be fine in the long run either (as long as you document what you choose to use on the back). One concern would be that in places where the acrylic has seeped through the canvas weave, the RSG might not adhere well to these areas. Conversely, the canvas could also become less absorbent overall, therefore making your RSG layer function more like a coating (which is more problematic) rather than a size layer.

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    ​​We are sorry that you have had some challenges with varnishing...believe me when I say we have all been there. We would not recommend trying to remove the varnishes at this point. It is actually fine to apply a varnish atop a matte varnish however you essentially are defeating the purpose behind applying the matte varnish to begin with. Generally speaking you are better off applying a gloss varnish first and then spraying a matte varnish on top later. In your situation we suspect you might have started to dissolve the matte varnish in some areas, creating an uneven surface and possibly those "sinking" areas that you have described. What do you mean exactly when you say that your painting "started to dilute a bit"? Were you pulling up paint? Were the paint layers starting to dissolve? In any case we recommend NOT removing your varnishes at this point but instead to try and apply a very even, thin application of matte varnish (spraying NOT brushing). We also encourage you to read our document on Varnishes which can be found in the Resources section for future varnish choices and decisions.

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    ​We are not sure what you are comfortable using but there is an excellent article on Golden's website here that may be of interest. There is some information on how to generate cells using isoproponal which you might recognize "scent-wise" in ordinary rubbing alcohol....so if you are able to withstand smelling rubbing alcohol you might try to use isoproponal in your work. We will also reach out to some of our colleagues who are better versed in cell creation than we are.

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    ​No, not all paintings will crack....all of the criteria you have listed is precisely what we advise so artists can try to avoid cracking from occuring. It is admittedly a hard thing to avoid but by following certain steps one can significantly diminish the chances of crack formation...however a couple things you did not list is a) complex stratigrapy and b) layer thickness. The more complicated the layering, the higher the probability to cracking will occur. Paintings that have thick layers continuous applied across the entire surface are also more likely to crack rather than paintings that contain isolated areas of impasto. This is not to say that artists should not paint thickly, it is simply an observable characteristic of thickly painted works.

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    ​To our knowledge MS2A varnish is no longer being manufactured. Conservators have been stockpiling this resin for sometime now since Linden Chemicals stopped producing the resin. We advise using Regalrez (Gamvar) or Golden MSA varnish if you are looking for stable proprietary varnishes.

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    Yes indeed and we agree with Mark Gottsegen's thoughts on this as well. While one can certainly use an acrylic medium and/or a pH-neutral PVA adhesive, BEVA is still probably your best bet as far as reversibility goes if you are going to adhere your painting to a rigid support. We have instructions on how to prepare your canvas in this manner in our Resources section in the "Rigid Supports" should you be interested.​

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    Well sorry to say that there is no ONE way to go about doing this...it depends entirely on the work of art, the exact acrylic emulsion, and the strength of the bond. All of these things have to be weighed carefully which is why trained conservators must do extensive testing each time to get a sense of what can be used that is safest for the artwork. Therefore our advice in this case is to simply consult with a trained conservator. They may be able to do the testing with you and then walk you through a potential treatment scenario that you can then carry out yourself. But without doing these tests and examining the paintings ourselves it is really impossible to give a "recipe" here...things could range from solvent-based to aqueous-based, getting very, very complicated (e.g. ph-balanced emulsions with chelators and buffering agents....well you get the idea).

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    I would not expect you (or others) to have ​experienced any issues with varnish removal...at least I certainly hope not at this stage! It is far too early in the lifetime of a painting to attempt to remove a varnish unless absolutely necessary. What may be problematic is varnish removal further down the road as I stated above. I suspect that Geneva does not add driers to their paints and probably adds just enough clove oil to create the desired effect (and therefore avoids the creation of unwanted "sticky" fillms)...but without additional testing it is hard to know what kinds of problems may occur during future varnish removal. Again I emphasize that the field of conservation would be well served to look further into such matters...one can find similar claims made by artists who are wetted to Maroger mediums...that they are stable and will withstand the test of time. However we know full well that such paint films remain soluble for many, many years and are sometimes impossible to safely clean (again, the problem of varnish removal comes up). I suspect it is much less of an issue with clove oil but I would still recommend recording the brand and/or material you use on the reverse so that future conservators will know to tread lightly (even though trained conservators ALWAYS read lightly ;) ). 

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    ​Actually we would LOVE it if someone in the conservation field were to conduct a study to look into concrete numbers regarding paint additives...so I will just leave this statement here for my conservation science colleagues to read (and hopefully someone will become inspired!). The information in our document is based on actual experience with cleaning works of art...both from our own experience and anecdotal evidence provided by other conservators. Every so often we will encounter a painting by an artist who is known to have used clove oil or a painting that lists clove oil on the reverse as an ingredient in the paint. Many of these paintings have proven impossible to safely clean, meaning the yellowed, degraded varnishes used to coat the surface cannot be removed without causing irreversible damage to the paint layer. Clove oil is an attractive additive BECAUSE it hinders drying...but adding too much can create a film that remains sticky and does not form a cohesive, healthy paint film, one that will remain sensitive to even the mildest of solvents. Most likely adding a drop or two to a substantial amount of medium is not the end of the world, but artists often add far more than is necessary in order to combat the drying processes. As with anything that is potentially problematic we simply request that you record your use of any materials/additives on the reverse of your painting so that your work of art can be properly cared for later on down the road. It may be possible in some cases to remove a degraded surface coating from your painting using aqueous methods, for example (should your painting require such a treatment...remember just because you might use a stable varnish does not mean that someone else will refrain from re-varnishing your painting later on down the road), something that a conservator would know to look into if they know that an artist used something like clove oil as a paint additive. 

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    ​To be perfectly clear from the begining, this procedure is not optimal, as you already mentioned.

    I think that the answer to your questions is yes. Just to be sure we are on the same page, I would not suggest sizing the hardboard panel with animal skin glue and then use acrylic dispersion medium for adhering canvas. This may cause problems as well and there would be possible incompatibility (or at least solubility and dry time problems and issues). In place of this you could size each size of the panel with the acrylic dispersion medium and then adhere the rsg sized primed and painted canvas to this panel using the acrylic dispersion medium. Done carefully, this should work fine, or certainly as well or better than the using rsg to glue the canvas.

    On the final though, varnish will likely slow down the penetration of moisture into the stratigraphy but it would not really stop it. If this were the case, the hygroscopic nature of animal glue would be not issue at all when used on panel paintings. A final word of caution, though. Care needs to be taken to restrict unrestrained movement of the canvas (weighing, etc) to prevent any subsequent shrinking during the process (this is why we always suggest adhering the canvas to panel before painting) to prevent damage to the ground and painted surface.

     

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    We are very happy that you find the site useful. It is true that the conservation field would like to persuade artists from using RSG because of all of the issues you are well aware of. I also understand the reluctance of some artists to abandon this material due to the qualities it imparts to stretched canvases.

    So let’s ignore those issues for the moment and focus on the suitability of using animal glue to adhere a finished painting to a rigid support. First, as you suggest, it is far preferable to adhere the canvas to the support before painting. You know this as well, so let’s move on. In the situation you outline, I would strongly suggest that you use an acrylic dispersion medium or gel in place of the RSG. It is less likely to cause issues in the canvas while drying and creates a far better bond. Animal glues are very strong and have great adhesiveness but are poor gap fillers. When gluing canvas to a rigid surface, it is generally far better to use an adhesive that good cohesion and fills the interstices of the reverse of the fabric rather than an adhesive that has amazing adhesive strength but is a poor gap filler. We do cover this subject to some degree in our RESOURCES section under Rigid Supports.

    When possible, it is preferable to avoid introducing moisture to a completed painting or one that contains an animal glue size. Water added at this point may cause uneven buckling. This is not always possible and is one of the reasons why it is best to completely prepare the canvas/panel substrate before painting. You could possibly use a thermoplastic heat-activated adhesive like BEVA 371 as well but that would depend on the surface texture of your painting and the degree of impasto. I also suggest that you allow the painting to dry for some time before even thinking about applying heat to the surface. Again, you can read more about this in our Rigid Supports PDF.

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    ​As far as ASTM (I being excellent, II being good, and so on) ratings go, yes, the binder and presumably the AMOUNT of binder matters. I include an excerpt from our "ASTM and Lightfastness" document in the Resources section here:

    It is important to note that the lightfastness of a particular pigment can differ with the vehicle used. For example, Vermilion has a lightfastness rating of I (excellent) when mixed in oils and acrylics. However, in a watercolor vehicle, it has a rating of III (fair). For this reason, one should check the lightfastness rating for both the specific manufacturer and the medium.
    PVA would probably be fine as well...but be sure it is a pH neutral PVA resin. And while no one (presumably) would be cleaning your works with a damp cloth, realize that paper conservators bathe prints and drawings all the time but ONLY after extensive testing is carried out on pigmented areas to determine stability. This is done routinely to rid the paper of yellowed/discolored material associated with acidic fractions that can form within the paper substrate as it ages, to diminish the appearance of tidelines should the work of art come into contact with moisture and/or a liquid substance, and then there is local application of moisture/aqueous cleaning agents that is done to remove mold growth or stains. If any color comes up during testing the work of art is essentially declared too fragile to clean and may not end up getting selected for an exhibition, etc, etc. But if the work is properly stored, framed, and notated on the reverse it should fare uch better in the future.

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    The stability of lean paints created by over-diluting aqueous binding media is tied to the absorbency of the support. As you state, the more “open” the network of fibers in the paper support, the better off you will be. One simple way to test whether or not your artwork might face problems in the future is to gently rub the surface of the painting using a soft cloth after it has dried. If a substantial amount of color comes up then the painting is indeed under-bound and there may be preservation issues.  However, if only a very minor amount of pigment comes up then you may be able to get away with your system as long as the piece is properly protected from abrasion (and during transportation and handling) so framing would be key here. One thing to note is the lightfastness of the pigments you are using. To a certain extent, the binder plays a protective role in slowing down or even inhibiting unwanted fading/color changes. Obviously, with the pigment-to-binder concentration at the level you are considering working at, there would be a minimal amount of binder. This can be an inherent problem with media like watercolors/gouache, which is why many museums display these works at subdued light levels. So again, looking into UV-protective glazing might be worthwhile here.

    As far as varnishing goes, this is really an aesthetic decision. Varnishing a lean paint film like one you suggest would create a relatively matte, undersaturated color effect. Varnishing would drastically darken and saturate such paint. This effect would be rather permanent as well as it is difficult to completely remove varnish from a very matte “thirsty” surface. A thin spay fixative may create less of a color change. Unfortunately, we cannot endorse many of the proprietary fixiatives available, as we do not know precisely which resins they use. I do think that B-72 is a good resin for this purpose. The availability of B-72 in a spray can in discussed in this MITRA thread:

    https://www.artcons.udel.edu/mitra/forums/question?QID=200

    It is possible that fixatives offered by Krylon or other brands are fine (they probably consist of acrylics that are stable for the most part). No matter what you choose, please record your painting methods and materials choices somewhere on the reverse of the piece, or the frame, so future owners and conservators are aware that it was the artist’s decision to varnish the work, NOT a dealer or someone else down the road.


    Kristin deGhetaldi and

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    ​​​So first to address the notion of a "sealer"....I guess what you mean by GAC 100 not really being a sealer is that it will produce a slightly porous film. Additionally, being water-based GAC 100 may contribute to the warping of thin panel substrates. If I were leaning towards using a water-borne size, I would likely go with a couple of coats of GAC 400 applied to both the front and the back (I believe this is detailed in full on Golden's website). It is also true that a solvent-born size (such as this particular shellac primer you mention) is far less likely to cause warping of the panel. Resins dissolved in solvent tend to create a more continuous, non-porous film than do dispersions such as GAC 100. However, in practice this is probably not a huge issue as you will ultimately be applying an acrylic ground atop whatever size you choose. In general it is best to treat the front and back of your panel in a similar way in order to avoid short-term warping.If I were interested in looking into a non-aqueous sizing material to use on a panel I would explore using solvent-borne acrylics such as Paraloid B-72 dissolved directly into ethanol/acetone and apply in one or two layers. The reason for this is that even bleached Shellac does show less than desirable long-term aging properties, despite some opinions to the contrary. Again, in practice this is probably less of an issue if the shellac is used as a size as compared to a surface coating.
    We are slightl confused about the mention of ammonia...the last time we checked (albeit some time ago) the BIN was a pigmented shellac dissolved in ethanol. Perhaps we are not up to speed on this...I tend to think of ammonia being present in dispersions and emulsions. 
    As for the size/thickness of your panel....the thicker the better of course but you will absolutely need some form of bracing on the back. Please refer to our "Rigid Supports" document in the Resources section for additional info on panels and possibly the "Adhesives and Sizes" document as well.

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    Probably we should avoid the phrase “forced drying” in this context, and reserve that for paints that either dry by evaporation, or in the case of oil paint, the addition of catalytic metal driers. As you know, oil paints dry by oxidation. In this scenario, the light, and consequent heat, may slightly speed up the oxidation rate (due to the fact that higher temperatures will increase reaction rates) as well as the action of UV light accelerating aging. If taken to extremes, the speed of reactions will be increased more at the surface of the paint than below the surface. This does occur naturally in oil paint films because of the greater availability of oxygen at the surface, but, in theory, you are only exacerbating this with prolonged exposure to heat and unfiltered light.

    The effect in reality is probably minimal beyond perhaps jump starting oxidation reactions. I do think that most of the impact of sun is to bleaching out some of the components that contribute to yellowing. Prolonged light exposure should be avoided for obvious reasons including the Increasing fading of sensitive pigments.

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    ​We recently had a very similar query come in regarding this topic (one that dates back to the time of Jan van Eyck in fact). We recommend reading our response on the other thread which you can find here and let us know if you have any additional questions.

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    ​Well if not for number 3 we might be able to offer some tips regarding the other issues. It is of course possible to paint without solvent....it just takes some getting used to. As far as driers go, unless you are using solvents and getting paint (with solvent) on your hands, there is very, VERY little chance that such materials would transfer through the skin. Same with oil paints containing lead, cadmium, cobalt, etc. Of course you can always wear gloves. But it sounds like acrylic is something that helps you to ease your worries so there is no problem with that. Many of us have already stated above our concerns about painting over a layer that is rich in retarded so as long as you are aware of the risks I would just encourage you to record your materials and techique on the back of your painting for future reference.

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    ​The last User comment (with time stamp 2017-04-10 23:55:32) would be George O'Hanlon from Natural Pigments...
    But I would say "Yes," anodized aluminum is likely fine but we really cant say for sure without doing more testing. 

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    ​Are you avoiding using oils for any particular reason? Perhaps for health concerns?

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    ​It really depends on how "yellow" your painting is and (as you stated) the presence of any pigments that are fugitive. We do not recommend exposure to direct sunlight only indirect/diffuse and preferrably near or close to a window. We would advise checking on the painting one day at a time and to not continue to expose the surface any longer than is necessary.

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    ​Based on Matthew and Sarah's comments above as well as my own understanding of retarders I would be inclined not to lay down an initial layer of retarder and/or add too much retarder in general. I think they have already outlined some of these issues but I would reiterate that even if a layer of retarder is below an acrylic layer with an appropriate amount of retarder, the lower layer could very well effect the integrity of ANY of the films above it....if the retarder has nothing to "retard" then any subsequent layers on top may have a hard life in the future. But perhaps this is what you are going for? You can certainly experiment but I would consider what folks have stated here....if you do decide to go that route it would be great to record your technique/materials on the back of the painting, not just for future preservation but for yourself as well, to help keep a record in case future problems should arise (or even if everything works out). 

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    ​These are all very good questions...in the sense that they are unanswerable from the point of view of a conservator simply because not enough time has transpired for us to say one way or the other. This is why we tend to lean towards the more "conservative" suggestion of adhering a canvas down first JUST in case there are issues later on down the road. But there very well may not be any problems...in either case do consider recording whatever you choose to do on the back of your panels.
    The point of the primer coat is to promote better adhesion...but if tests demonstrate that certain methods are working fine without a primer (I recall that earlier tests using true gesso, meaning animal skin glue, did not pan out and lead to cracking and delamination) then the primer coat may not be necessary for certain layering systems and/or certain types of aluminum substrates. Hopefully some of our other moderators will weigh in on this...I will also try to reach out to some objects conservators who may be able to shed some light as well.

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    Hi

    I was born in Michigan and remained there until college so I am well aware of the crazy weather including temp and humidity fluctuations that the state endures. I mention this because this is clearly what caused the relatively temporary planar distortion you observed in your canvas. The most likely culprit here is the huge variation in relative humidity that the canvas experiences. First, is the painting on an exterior facing wall? If so move it to an interior wall. You would be surprised how much of a difference this can make, even in a weatherized house. Moisture will still transfer through the wall and, consequently, the painting. No matter what, installing a backing board on the painting to help mitigate the effects of the transference of moisture through the walls. Please visit our document entitle “Storage, Exhibition, and Handling Tips” in our RESOURCES section.

     

    As this is an acrylic dispersion painting, which are generally quite flexible, I would not personally put your work through such a drastic procedure as you suggest. I would probably try what I indicated and see if it reacts differently next year. If the same thing occurs or you really just want to “nip this in the bud” we do have instructions on how to marouflage, the term for what you suggest, in the RESOURCES section under “Rigid Supports”.

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    Just wanted to concur with Matthew Kinsey, from Utrecht, about the distinction between a retarder and an extender/medium, ​an issue I really did not address earlier. As Matthew pointed out, putting an excessive amount of Retarder into a paint film - with our products, we recommend no more that 15% Retarder - can result in a persistently sticky, water-sensitive film. Assuming that you do not have that problem, and the film feels fully dry to the touch, we would still recommend testing for water-sensitivity just to be safe. Especially if you suspect that you went well beyond the maximum recommendations of the various brands. To do this, as mentioned before, just use a wetted cotton swab and rub slightly, looking for color lift. If nothing comes up, you are likely fine. If you get staining, then carefully applying a light coating of an acrylic medium of some sort should seal it in. If you get excessive color lift, or have a powdery surface, then you might need to first consolidate and lock down the surface with a light spray of something similar to our Archival Varnish aerosol, and then follow with an acrylic once allowed to dry for 24hr.

    Hope that helps  -

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    The main concern with painting on ACM panels is always adhesion. You want to ensure the surface is prepped in such a way that you do not encounter scaling, flaking, delamination, etc. down the road. In the meantime we have sent your query out to some who are more knowledgable in this area who may be able to weigh in with their expertise.

    So anodized aluminum surfaces can really range in the sense of composition (e.g. is the aluminum sheet itself an alloy as opposed to pure aluminum? You might want to avoid any zinc-containg alloys for example), pore size, and the method used to seal the pores after the anodizing process has been completed. So it is really hard to say whether one particular brand/type is better than another without doing a number of tests.

    In principle we feel it that painting on these surfaces would not pose too many risks if the surface is properly prepared. For surfaces that possess polyester coatings (an alternative to anodizing that industry uses to counteract potential corrosion) we recommend degreasing, lightly scuffing the surface to provide tooth, and then applying subsequent layers of primer and paint. We are unsure at this point if lightly sanding the surface of anodized aluminum would be necessary or even a good idea (just as with polyester coatings you do not want to abrade TOO heavily as you risk removing this protective layer entirely). This may very well depend on the thickness of the anodizing layer. But you could certainly ask your manufacturer whether using a 320 grit sandpaper (which is what we recommend for polyester coated ACM…you may need to use a finer or coarser grit depending) would ever get you close to the bare aluminum underneath for a particular brand of anodized aluminum. As for painting directly onto the surface without sanding, again this would require additional tests for any given brand. If the manufacturer states that it is alright and you chose to forego performing any tests yourself then things might work out fine….if not then the manufacturer should not be surprised when they receive an unfortunate phone call from you.

    Even though we tend to advise folks to steer clear of most industrial products, sometimes there are certain instances when one actually SHOULD turn to industrial products to ensure the longevity of their work and with ACM this can certainly be the case. DTM Bonding Primer by Sherwin Williams has been tested and found to be a suitable primer for ACM, a primer that can then be covered with a layer of acrylic gesso (followed by acrylic or oil paints).

    For piece of mind you can always adhere a canvas to the support first before applying any size/primer, ground, paint, etc. That way should there be any issues in the future the canvas support can be safely removed from the problematic ACM panel and simply re-adhered to another rigid support. There are instructions and additional information relating to this process as well other aspects of ACM that can be found in our "Rigid Supports" document in the Resources section. 

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    ​First, it's important to understand the difference between "retarder" and "extender". Acrylic mediums that are sold as "extenders" contain the same polymer dispersion base as acrylic colors, so adding a lot of medium doesn't result in a weaker film. Alternately, most retarders for acrylic paint are not acrylic mediums; they are mixtures of propylene glycol, water and gelling agents. Glycols act as coalescents in acrylics, moderating the rate as which the film forms and achieves full integrity. Adding extra glycol and water-gel keeps paint wet longer, which is advantageous when painting outdoors on a hot, dry day, or when more suave blending is desired. Since retarders don't usually contain any acrylic dispersion base, they don't reinforce film strength the way acrylic mediums do, so use of the minimum effective amount is recommended. Excessive use of retarder (with our product, more than 25% by volume) can result in a porous film that stays sticky for a long time, and which permanently becomes tacky in warm display/storage conditions. Professional-grade artists' acrylics can be thinned with quite a lot of water and still achieve a durable film, but I have seen really watery, thin applications that don't adhere well. Thinning with a lot of plain water also temporarily lightens mixtures, making it hard to judge the final appearance from palette to canvas. Low-viscosity mediums (e.g. Acrylic Sizing and some of the GAC mediums) added to thinned paint can boost adhesive power, plus help reduce the difference in appearance between wet and dry colors.

    Matthew Kinsey Utrecht Art Supplies

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    Hi -

    Similar to Brian's reply we would want to understand what you mean by "over extended" in terms of water. This is especially true as this is an area that is likely in our top 5 misunderstandings, at least in regard to our acrylics and likely other professional brands. In terms of Golden acrylics, our standard Heavy Body and Fluid acrylics can easily be thinned by up to 1:1 with water while still producing a very durable film. And in fact in many tests on Plexiglass - a very nonabsorbent surface - we still had good adhesion at ratios of 1:2 and 1:3 paint to water ratios. So acrylics can take a lot of thinning and still be fine. And then too a lot depends on the conditions of application. For example, dilute a tablespoon of acrylic paint in a gallon of water, then let evaporate, and you will find that you still end up with a fine acrylic film at the bottom of the bucket! The reason being that the initial dilution is still quite contained in area.

    As for your concerns, if worried you went too far in thinning, one quick test would be to rub an area lightly with a wetted Q-tip and see if there is color lift or an obvious powdery surface. If yes, or if just wanting to play it safe, you can carefully apply a layer of an acrylic medium over the surface and that will fully consolidate and lock in the area and allow you to freely apply more acrylics or oil paints on top. In the case of oils, however, we would recommend something like our Fluid Matte Medium as a form of 'clear gesso' that will provide adequate tooth and adhesion for oils.

    And if misunderstanding your concerns somehow, or you have further questions, just let us know.

    Hope this helps!

    Sarah Sands

    Senior Technical Specialist

    Golden Artist Colors 


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    We are sending this question to a few of our moderators who are more directly involved in acrylic dispersion media but I will attempt to provide a preliminary response. First, I do need to ask what you mean by too much extender. Are you adding additional clear acrylic dispersion medium to the paint? If that is the case, you are not really diminishing the binder and the paint film should remain resilient. If you mean adding a dry powder like chalk or additional pigments to the paint, you are in essence raising the pigment load and weakening the binding strength.

     

    First, to my mind, I think that we need to separate the issues of acrylic dispersion paints that are thinned with too much water with that of adding too much retarder. The first is a physical alteration while the second is also chemical. I cannot really comment on the latter and we will have to wait for someone with greater expertise in this area.

     

    I do think that applying a thin dilute layer of acrylic medium over the underbound paint could help to stabilize the layer. Generally, applying a fatter paint layer over an overly lean layer does not always solve the problem, this is certainly true of oil paint, but even in that circumstance there are times when it is helpful. To be clear, though, one should never apply straight oil over a layer of oil paint unless this area will receive subsequent layers of pigmented paint (see our “Varnishes” document in our RESOURCES section for more information about “Oiling out”). The use of clear surface applications of medium is far safer in acrylic dispersion paints where the yellowing of the binder is relatively insignificant.

     

    The answer to “b” is likely similar but I will leave this to those more experienced in acrylic dispersion paints. Probably the medium heavy application of additional acrylic dispersion paints would work. The efficacy of the superimposition of oil paint would depend upon the degree of stability of the lower acrylic dispersion paint layers. Likely, a lean acrylic underlayer would function similarly to a lean acrylic ground and the results would be satisfactory. An extremely underbound layer, however, may be so thirsty for medium, or so friable, that either the top layer of paint is drained of its binder or the adhesion to the lower layers is compromised. Again, others may be able to provide a more precise answer.

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    To our knowledge there are no images out there floating around that demonstrate "oil rotting on canvas"...although some of our conservation colleagues that work with archaeological or ancient textiles may have some evidence/information that we are not privy to in the paintings world. But with fabrics of significant age it can be hard to pinpoint one factor and one factor alone that might have accelerated certain degradation processes....this is why we still feel it is a topic that is up for debate when it comes to traditional easel paintings.
    As for the presence of fillers/pigments you will still have the same chemistry at play. Painting directly on top of an unsized and unprimed canvas will still involve some sinking of the oil medium directly into the overabsorbent canvas beneath. You would also risk creating an underbound paint layer to boot. But as to whether these reactions would happen to the same degree it is hard to say...it likely depends on the pigment-binder ratio and what type of pigments/fillers are present. Hope this is somewhat helpful!

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    First it is always a good idea to size. But obviously this is a choice left up to the artist. Directly relating to the earlier query posted here, we have actually been discussing the topic of "oil rotting canvas" recently and truth be told this topic remains one that requires further study. Such concerns can be traced back among artists for hundreds of years. Yet at the same time there are many, many examples of unsized paper (so made with cotton and/or linen fibers) that printmakers used as primary supports for oil-based prints (intaglio, lithography, etc.) that are hundreds of years old and in spectacular condition. HOWEVER there are certainly concerns regarding the chemistry involved with oil as it ages and degrades over time and the adverse affect that it can have on cellulosic fibers.

     

    This excerpt taken from the Chemical Principles of Textile Conservation (pg 117) may be of some interest:

    "When applied to a textile without a size, the liquid oil binding medium may penetrate into the fibers and impregnate the textile around the painted pattern. During network formation the oil film may shrink. The staining and shrinkage can damage both the appearance and structure of the underlying fabric; fibers can be damaged by the hardness and deterioration of the oil film. The presence of the peroxide crosslink in the film can result in chain scission of the carbon chains. The peroxide crosslink is a weak one, hence it readily undergoes ruptures caused by environmental heat or light. When the peroxide crosslink breaks the carbon to carbon bond located in the alpha position to the peroxide crosslink may also break. The resulting radicals may quickly undergo oxidation. […] The increasing acidity of the deteriorated oil layer may cause not only further fragmentation of the oil network but also hydrolyic breakdown of fibers, when it is in contact with cellulose, such as unsized paper, canvas, or barkcloth."

    As for your image it does not appear to us that the areas designated with arrows are due to staining from the oil medium; however, it can be difficult to make these determinations from photographs alone. For the moment we still recommend applying a quality size and ground to your canvas before applying subsequent layers of oil paint.

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    ​​First let me just say I am so sorry that this happened to your painting. And unfortunately there is really no way to effectively remove/reduce such cracks without performing a more extreme procedure, namely adhering your canvas to a solid support (like ACM for example). As for applying acrylic medium/sizing to the reverse I would worry about potential planar deformations that might occur due to uneven application at this point since it is already stretched...have you actually started painting yet?

    Applying acrylic to the reverse may mitigate potential staining and/or damaging affects caused by the penetration of oil further down the road...that one is hard to say for sure but you risk causing the entire canvas to shrink and may even introduce uneven planar deformations. This may not be evident at first but it certainly might later on. If you MUST apply acrylic size, I would advise taking it off the stretcher completely but try to keep the canvas taught and planar throughout the process (so that would be a pain as well). If you do not you will likely end up with pronounced cracks corresponding to the outline of the stretcher bars as it will be difficult to get in between the stretcher and the canvas to apply the size evenly. 

    In the future consider making a backing board for your painting before you size and apply the ground layers. This will help to avoid any damage that might occur due to impact with foreign objects (it is an almost inevitable thing in studios). We have instructions on how to do so in our "Storage, Exhibition, and Handling Tips" document located in the Resource section should you need further information.

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    It is a bit difficult to tell what is going on from the image (but thanks very much for including one for clarification!)...is there any possible way for you to take a picture of the reverse in the same area that is displaying signs of this "dimpling" effect?​

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    Kevin and Sarah

    Sarah makes some very valuable points and I have no disagreement with them at all. She is spot-on when pointing out the benefit of removing the effect of changes in environment on the substrate. I do not want to make too big of a deal on this, but I do have some concerns about the pre-primed polyester canvases that I have examined.

    I will try to clarify my general feelings about polyester, especially very thin pre-primed fabrics, as a substrate for oil paint, and especially oil paint that is applied in any degree of impasto. Yes, the size and ground contribute much of the required stiffness for the painting. If we take this to the extreme, the same could be said of applying size and ground onto onionskin paper. A heavy application of size and ground would make this system “suitable” for oil painting. At a certain point, I begin to ask what the support brings to the table? Would it not be better to just have a thick slab of acrylic dispersion ground and forgo the overly flexible fabric all together? Yes, the polyester fabric does provide some “very minimal” texture but could this not be added to the surface of the acrylic substrate? I am intentionally exaggerating here to make a point, but I do think that it is a point worth considering. I also have similar concerns about all thin, flexible fabric supports and especially the very insubstantial, thin pre-primed fabrics ubiquitously sold in craft and fine art stores alike. 

    As to the available pre-primed polyester fabrics. Those that I have examined (and I likely have not seen them all) have been extremely thin and very flexible, almost elastic. To me, this does not equal the required degree of stiffness of support to make them suitable for oil painting of any appreciable thickness.

    Back to the Kevin’s original plan. As it is written, I see a very flexible substrate, if the canvas you are speaking of is in any way similar to what I have examined, with a layer of oil paint applied to it (in this system, the lead white ground will simply function as a preliminary application of quite lean oil paint). No doubt, lead white is very flexible but this gives me pause. On your finished painting the lead white ground and all subsequent oil layers with become more brittle with age and will be sitting on a potentially extremely flexible support (again, if the polyester canvas is similar to others that I have seen). I am not sure if we can say that the polyester’s lack of response to environmental changes justifies this situation. I personally err on the cautious side of thi for the moment.

    Now I do not want to tell you that you should not follow your proposed plan. It may turn out that the system you mention will work perfectly fine for your work. I simply have the above reservations. Additionally, I do want to give the impression that I am extolling the virtues of linen and cotton in general. The use of a heavy polyester canvas with less inherent flexibility (or one with a substantial size and ground layer, which provides a good degree of stiffness). This may really be a profound improvement for those who want to continue to use flexible, lightweight supports but want to diminish the effects of changes in humidity on the preservations of their oil paintings.  

    So those are my thoughts. I really welcome additional dialog on this issue. I am also very happy to change my mind on this if the research indicates it.

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    ​Just to share a potential workaround that, while not perfect, might be less problematic in some ways.

    When wanting to preserve some old newspaper clippings I found that doing a high quality scan and then getting them digitally printed (using something like Epson Ultrachrome of K3 pigmented inks) on archival artists' paper made for digital prints, gave a fairly good simulation of the original that at least visually, from some inches away, looked like the real thing. So while it does involve extra steps, and you are still faced with the less than perfect lightfastness of even the pigmented inks used today, overall this might be a more durable stand-in for use in collages. At the same time, depending on your philosophical stance on collage, it does mean not working with the actual original, more common materials - which might be problematic. But keep in mind that artists like Joseph Cornell was often quite comfortable with simulacrums of older things, with the visual end result being the most critical.

    Anyway, just another thought to share.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors



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    Seeing the evocation of "Dare to Be First" staring at me at the bottom of the Forum page, let me take up that challenge while waitting to hear Brian's thoughts as well.

    Given that cotton canvas, or really any textile, is already far more flexible than any oil paint film, especially as those films age, I think there are potential, positive tradeoffs in terms of the polyester canvas being less reactive to environmental changes. Also, like with canvas, the ultimate stiffness and flexibility of the support - and really the materials that will serve as the carrier of the painting overall - will be any sizing and ground that you use.  In your case we would think that initial coats of acrylic gesso followed by 1-2 coats of an oil ground, should provide a stiffness likely not far off from a similar treatment on  something like portrait linen. At the same time I have not looked deeply into what are the longer terms issues - if any - with polyester canvas experiencing creep or loss of strength. And one would still be confronted with canvas of any form never being the ideal substrate, so some risk will continue to be locked in regardless.On a final note, the late Ross Merrill, past Chief Conservator at the National Gallery of Art, was fond of using Sunbrella fabric as a support for his own paintings, which is a more substantial acrylic textile most commonly seen used for exterior awnings. See the following as one point of reference:

    http://cool.conservation-us.org/byform/mailing-lists/cdl/1999/0522.html

    So another option to look at that might be inerently less flexible and more durable, even, than polyester. but again, we have no direct testing of our own to go on.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    ​We recommend rolling the painting paint layer FACING OUT on a wide diameter tube (such as a sonotube....at least 10-12 inches in diameter). Glassine is really only suitable for short-term storage so it would be preferable (and safer) to use something like soft Tyvek or even volara. You can then cover the whole thing with Mylar for extra protection from the elements. Hope this helps!

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    Hi, our response would be along the same lines as those from Matthew Kinsey, from Utrecht.  In general water based materials are prone to the stabilization of foam, and in formulation defoamers are incorporated to reduce this issue as much as possible while not causing other surface defects. 

    As far as prevention, it really comes down to technique. Foam rollers - in an ironic twist on their names - are notorious for foam generation, as their pores force air into paint with each compression.  A fine nap roller will reduce this greatly, but in general we recommend trying to avoid rolling altogether if wanting a relaiablly foam free surface. Sprayting will always be the gold standard in this area, and while we realize that would represent an investment and learning curve, if wanting a perfect surface, that is by far the way to go.

    Hope this helps.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    ​Lefranc & Bourgeois recommends Flashe vinyl colors for use under oils and acrylics, so I agree that it should not be a problem used underneath acrylic colors. Regarding whether the two should be mixed: I think the result would be inferior to 100% acrylic paint, in terms of film strength and long-term durability. Vinyl emulsion was largely replaced in house paints by 100% acrylic and acrylic/styrene copolymer dispersions because the latter are more durable (e.g. less permeable to moisture, less vulnerable to UV light exposure). I would expect results in mixed paint to vary depending on pigment content, since some colors that may be present in vinyl paint can induce curdling in acrylics. Some crazing may also occur when layering acrylics over PVA products, because PVA can swell from subsequent wet applications.

    Matthew Kinsey
    Utretcht Art Supplies

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    ​While there are food-grade defoamers available to consumers that are similar to those used in the paint industry, I hesitate to recommend them since the analogous materials for paints can affect adhesion and film integrity when added in incorrect amounts. Before modifying the paint/primer, I would test different rollers. Manufacturers of architectural/house paints give guidelines for the best type of roller to use for diluted paints so bubbles don't form, so I think it makes sense to try this first. 

    Matthew Kinsey
    Utretcht Art Supplies

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    ​In short: it can't hurt. But no, sadly it will not completely halt the chemical degradation mechanisms that contribute to the build up of acidic components in these types of low-quality papers over time. There is a related forum discussin on a similar subject that you may find of interest here.

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    Either a high-quality acrylic dispersion gel medium or a pH neutral PVA adhesive would be good options.

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    ​Very good question...we have sent this on to some of our Health and Safety experts as well as our scientists on the Moderating Board so hopefully they will be able to weigh in with some useful information. I am inclined to say that you probably do not have much to worry about...you are using good practices to deal with proper waste disposal and as long as you have a devoted can for these purposes it should be alright. You might ultimately decide to ditch the can after a year or so however (at the same waste disposal facility) just to be extra cautious.

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    ​​Very good questions...our first inclination is that there really should not be too many issues with layering acrylic paints over these types of "vinyl" paints which are often more matte and/or opaque as you state above (acrylic polymers actually contain vinyl groups). As for your second question (inter-mixing) we really cannot say and have sent along your question to others on our moderating board that will likely be able to share some insight on this matter.

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    ​I understand the need for economy and the added benefit of keeping waste from landfills when saving paint for subsequent sessions, but it is also important to use relatively fresh paint. This is not like watercolor or encaustic where we can jusr resisolve the paint again and again. There are the issues that you mention including skins and dried bits getting into the paint. These is also the importance of having the paint go through its drying curve after it is aoplied to the surfeace rather than much of this occuring before it is ebven on the canvas. Ralph Mayer stated this well in his influential tome. We have moved on from some of his opinions but I think that his advise is best observed on this issue.

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    Honestly there are pros and cons to several "paint-saving" methods that have been circulating online. It is really a matter of considering the type and quality of oil paints you are using and what you can feasibly do within the confines of your studio/working space. Obviously if your paints already contain driers (as is the case with some brands and certainly with many alkyds), many of these "tricks" will not have a significant impact. But I will do my best to list some of the pros and cons one might  consider below:

    1. Freezing your palette – Ideally you do not want to store your paints in the same freezer as food! I realize this may sound obvious but there will always be some cases where folks do not have the luxury of having a freezer devoted solely to paint. If one is forced to use the same freezer for paint and food, your palette truly needs to be in a sealed container (e.g. tupperware) of some kind to avoid contaminating your palette (and contaminating your food!). As for condensation, I assume you are talking about the formation of the annoying water droplets on the surface of your paint/palette when you remove it from the freezer and it begins to reach room temperature. Unfortunately this is somewhat unavoidable but you can always place it in front of a fan while it slowly warms up to drive off the accumulation of moisture.

    2. Submerging your palette under water – Many people do this over night to avoid having their paints dry out. One benefit is that you eliminate the presence of air altogether, therefore slowing some of the oxidation processes that can contribute to the drying of oils. However, if your paints happen to contain certain additives (e.g. surfactants) or possess a high clay content (e.g. earth pigments like yellow ochre), prolonged contact with water might cause some issues. Certain additives might be drawn out of the paint, giving it a different consistency, appearance, or altering it in some other manner. When your paints contain a significant proportion of clay, the opposite effect can happen, with the paints tending to absorb water and behaving more like an emulsified mixture rather than simple oil paint (and perhaps leaving small, microscopic voids after drying).

    3. The clove oil strategy – We are actually somewhat skeptical as to whether placing a rag infused with any essential oil alongside your paint and then covering up the palette would actually have a significant impact at all. And honestly if it does this means that these oils are directly effecting the paint, likely in a manner that is not desirable if you are concerned about paint longevity and sensitivity. While the proportion of essential oil would likely be on the negligible side in this instance, additions of essential oils to oil paint can render a paint film more sensitive to solvents (should it need to be brush varnished again in the future or cleaned) and may even contribute to drying problems. We would suggest leaning more towards the other two strategies if you do opt to exercise some method of "paint-saving," taking into account the precautions we listed above.
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    ​Thanks so much Sarah for your insight on this...so this appears to be a separation of the finer pigments from the mica flakes, creating an optical green effect. Very interesting!

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    ​Hi! The Bronze is indeed one of the few Iridescents where we add a pigment in along with the mica-based Iridescents (the other two include Iridescent Bright Gold, which has Nickle Azo Gold and Quinacridone Red, and Iridescent Silver, which has Carbon Black). Because of that you can definitely get separation, especially in a wet and very fluid condition, where the pigment has time to settle out. We even call a little attention to this in its description on our website

    http://www.goldenpaints.com/products/colors/iridescent-colors/heavy-body-iridescent-colors/iridescent-bronze--fine

    where we mention that "it also creates a verdigris effect when used as a wash." So while you stumbled on this by accident, it is also something that others have used on purpose and to beautiful effect.

    We hope this helps but if you have other questions please feel free to ask.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    ​​Our experts at Golden will weigh in soon...but my first question has to do with your palette....what are you painting on? From the photo it looks to be a piece of white marble/ceramic...or perhaps a very white piece of paper? In any case, my theory is that you are witnessing the formation of some type of green copper carbonate around the periphery of your copper-containing metallic mica paint.....This could certainly happen if your substrated is something like smooth marble or even a buffered peice of tissue/blotter paper. BUT it is my understanding that these particular mica paints do not contain copper....so it is confusing to me as well....hopefully Golden will have some insight into this phenomenon.

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    Not necessarily....it really depends on your technique and how "resilient"​ your sublayers are. A fine grit sandpaper should be fine. I am copying this excerpt from our "Mediums and Additives for Painting" document located in the resources section that might be of interest: 
    It is inadvisable to paint a fresh oil painting over an abandoned work in oil as the surface may a) contain a buildup or surface dirt/grime b) contain a layer of protective varnish on the surface and/or c) not provide sufficient “tooth” or absorbency, leading to potential delamination or flaking. In addition, oil films gradually become more transparent as they age which will result in the underlying composition showing through in certain areas. If it is not possible to obtain a new support and start afresh, artists should consider removing any varnish coatings and scraping/sanding down layers of paint (exercising appropriate health and safety precautions) before applying fresh applications of oil paint. It is possible to gently sand the surface of oil/alkyd paint layers. Remember that inhalation of any type of fine, particulate material (particularly if hazardous pigments are present) is not recommended and that a dust mask should be worn during sanding. It is best to avoid and sanding or scraping of grounds containing lead or other toxic pigments. Once you are finished sanding the ground, wipe down the ground using a cloth dampened with odorless mineral spirits to absorb any remaining loose pigments/particles (be sure to properly and properly dispose of the cloth).

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    So sorry. We seemed to have missed your final comment on this. I do not think that a drill-based sander would be maneuverable enough to work for this without causing major damage.

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    There is no problem with doing this...you simply will need to eventually size and prime the exposed canvas (the side you will be painting on) in a manner that is similar to the backside. There is actually evidence of some painters in the past who have done this and there appears to be no negative consequences (the Pre-Raphaelites for example). The only downside is that you will have to wrestle with stretching pre-primed linen which can be a bit of a challenge at times...

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    ​Yes we are aware of the confusing terminology :) hopefully we have been able to provide you with some useful info to help you proceed...

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    ​Yes my apologies...the GEL medium would be better (thicker consistency).

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    ​The gelled form of acrylic dispersion medium is preferable as it fills any voids and can create a better bond. You could use a fluid medium as well, but I would go with the gel.

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    ​You CAN use Jade (PVA) but then again you adding yet another material into the mix if you are already working with acrylic gesso anyhow. Your bond will likely be more chemically "successful" if you use acrylic gel medium but you can certainly test a sacrificial piece of paper and try it out (after sanding the gesso a bit).

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    ​Actually these materials can be reversed (although not easily...and it takes having a Masters degree in conservation to know how to do it properly!)...Just to give you some possible scenarios as to WHY it may need to be reversed:

    1) The Birch ply support becomes compromised and develops splits/warping/cracks, etc. and risks imparting damage to the oil on paper.

    2) If the particular type of acrylic gesso is one of poor quality (there are many, many, brands out there these days) it may have an adverse effect on the oil on paper (although this is less likely to occur with a layer of good quality acrylic gel medium in between).

    As per your second question...yes we mean for you to use the fluid acrylic gel medium....the kind you can add to acrylic paints. I would avoid using matte although it would likely work as well...matte mediums tend to be bulked with fumed silica and have a toothy surface when they set...this would make for a less successful bond with your paper substrate.

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    ​Your first question: Yes this is what we mean by sizing/priming the paper.
    Second: It would likely be fine to use your primed birch panels...were these purchased pre-primed or did you prime them yourself? You might make a note of this on the back of the panel (including any of the other materials you are using) as this would help to inform future conservators should your oil on paper need to be removed. You should consider lightly sanding the acrylic gesso to get a smoother surface, then apply a layer of acrylic gel medium to cut the absorbency. Wait for this to dry and apply another layer of gel medium before adhering your paper substrate (following the same directions as above).

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    ​Hi Jeremy...I have forwarded your request along to our IT point person. In short we would love to have this type of feature associated with our forum and perhaps there is a way to do it. So stay tuned.

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    ​If you are interested in learning more about how to prepare your own backing board, instructions can be found in our Resources section in the "Storage, Exhibition, and Handling Tips" document.

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    This practice is almost uniformly condemned today. It is less of an issue of the fibers needing to breath. The more important reasons are twofold. The application of materials to the reverse of the canvas can create brittleness in the case of Japan size. This may also rot the canvas overtime.

    Additionally, whenever you adhere something to a portion, as opposed to the complete, verso of the canvas you will eventually see that impression of that material telegraph through to the surface resulting in a topographical bulge in the shape of the applique that can be seen on the front of the painting. You have probably seen patch shaped bulges visible on the surface of poorly restored paintings. I have also seen this happen with gallery labels that were stuck on the backs of exhibited paintings. This is all just the result of the inevitable natural alignment of physical forces that occur when a smaller objects is attached to a larger and flexible object. The same does not happen with lined paintings but that has its own issues.

    The tinfoil idea would not be terrible as long as no adhesive was used. Today, we generally just attach a rigid, vented backing board (eg Fomecore or acid free blueboard) to the reverse of the stretcher. This does almost everything positive that the earlier procedures did without any of the negatives. BTW the small vents left in the backingboard prevent the creation of a micro-environment which may occur in very humid environments.

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    I do believe that what you want to achieve is doable. First, if I had my way I would suggest a heavier weight, cotton rag paper to begin with but the 140 lb. will likely work. The heavier the paper, the more rigid the primary support. The wooden secondary support will help to offset this.

    I do not think that this is overly complicated.   You should make some tests first to determine if the adhesive will stain or change the appearance of the paper substrate. Make sure to test any adhesives that you intend on using on a scrap piece of the same rag paper that is sized or coated (eg with an acrylic dispersion “gesso” ground if you used one). The wooden panel should be well sized, I would probably use an acrylic solution like B-72 in acetone (or a spray like Lascaux) or an acrylic dispersion gel medium. Let this completely dry before moving on. One could also use a PVA dispersion size. I would then adhere the paper support to the panel with an acrylic dispersion gel medium if that passed your initial test. Care must be taken to make sure that the paper does not wrinkle or developer a fold when you are pressing it to the panel. You should gently press the paper to the panel starting from the center towards the edges. You may even use a brayer as a last step as long as this is done very gently. Remove excess adhesive that has oozed out around the edges of the paper. I would cover the face of the painted paper with a blotter and weigh down the whole for a day or so to eliminate the chances of buckling or warping.  

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    Again, you are not completely wrong about the contradiction. Adding larger and larger amounts of fast drying alkyd mediums to subsequent oil paint layers does mean that the top layers would dry faster than the lower layers. In practice, this is a matter of degree. Small incremental differences will probably not cause a major problem in terms of drying differences and the added flexibility of the later layers would conform to the preferred practice of more flexible on top of less flexible.

    Alkyd mediums have been in use for a relatively good length of time and the practice of judicious additions these to traditional oil paint does not seem to have caused problems.

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    You are correct about the conundrum. It is generally best to have lower layers dry faster than upper layers and to have upper layer more flexible and generally fatter than those below them.

    I would suggest that when adding medium to a paint, as opposed to underpainting with pre-made alkyd paints which contain a minimum of binder, you only use it in the final paint layers. In ala prima paintings this may be the first layer and in more complex paint layering it may be the 7th or later layer. This also means that you should really let the lower layers dry well before applying the final layers. You should also refrain from using poor drying and weak film forming paints in the lower layers unless they are a part of a mixture containing better film forming paints (ie ivory black should have a good amount of white added to it when used in lower paint layers)

    Does this clear things up at all?

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    Koo,

    In retrospect, I think that my answer was far less than satisfactory. I will correspond with some individuals more familiar with the chemistry of gum Arabic and give you a more precise answer.

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    ​Koo,

    I really only mentioned the solubility issue for completeness. The amount of gum Arabic is likely very small in proportion to the egg in actual practice. Yes, egg yolk is an emulsion containing proteins and oils (as well as many other components including lecithin as an emulsifier). The egg yolk film becomes water resistant rather quickly and more so overtime. Gum Arabic is more brittle than egg at least initially. I am less sure about the precise aspects of the long-term aging of gum Arabic but I doubt that it becomes drastically more brittle overtime. Again, the small percentage of the gum that would be in the final egg tempera paint would probably not greatly change the relative brittleness. Again, this is all just mentioned for full disclosure.

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    ​Thanks again Koo.

    I do want to point out that egg tempera made from watercolor and egg yolk will be ever so slightly more water sensitive than pure egg tempera. This is unlikely to be a major issue, though.

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    ​Soaking newspaper will likely just result in accidentally making paper pulp....something I doubt you want to use in your collage. If you are painting in acrylics you could opt to coat the newspaper in a clear acrylic gel medium and then adhere to your panel/canvas...that would honestly be one of the better ways you can "encapsulate" some of the inherent acidity of the paper. As you can see from other comments posted earlier newspaper is made from poor quality paper to begin with as it's intended lifespan and period of use is not super long.

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    ​Koo, as always. Thanks for the informative post.

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    ​The following is some information from one of our moderators Hugh Phibbs...it should be noted that while you can certainly use these products, there are a few things that conservators are still unsure about as more research is really needed to confirm whether these products achieve what they purportedly accomplish. As Hugh points out, adding additional chemicals may help but they may also interact in an unforeseen manner with any additional paints, coatings, inks, etc. that you choose to use in your collage. It is possible that simply protecting them from the air by covering them with a varnish of some sort and/or by placing your collage in an appropriately prepared enclosed frame. Here are some of his thoughts: 

    The idea of lowering the pH of ligneous paper has gotten a great deal of attention, in the last fifty years and has inspired Wei ‘To and Bookkeeper, both of which include solvents and alkaline buffering. I have always advised against this idea, for a number of reasons. Insuring that the alkaline  material gets to the interior of the item is hard to accomplish. Soaking the item can work, but too often they are sprayed on and the item may get an uneven coating, meaning that it is likely to age unevenly. Another problem is the reaction of the acidic oil in the ink, with the alkaline component and the creation of soaps. Ultimately, the questions of reaction with all the non-cellulose components of the artifact, bother me a great deal, since the problems are likely to continue, after the alkaline component has been exhausted and salts and soaps remain in the artifact. The approach that interests me is reduction of oxidants and I have seen very old news print that is still in good condition, when it has been kept from the air. 

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    ​Hi -

    We have added a listing of the pigment densities used in our colors on our website, which you can now find here:

    GOLDEN Artist Colors Pigment Density

    or access it through the Application Section of our Technical Info page:

    GOLDEN Technical Info

    Let me also add a few words in terms of why we chose to share Pigment Density rather than Paint Density.  In pours and other applications where pigments can either settle or float in different ways, it is really the pigment density at work more than the density of the paint overall. And then, of course, paint density quickly changes the moment one adds any water or medium, or even from evaporation of water whhile sitting out. Pigment density by contrast stays constant. 

    It is also important to note that even pigment density will only predict behavior so far. For example, there is the impact of particle shape (especially with mica-based ones) and the fact that simply dropping paints into a medium, or even thinning them down with water beforehand, will not mean the pigment will be stripped of the various components we use to keep them in suspension. So you are almost never truly dealing with the pigment as an isolated pure solid. That said, this info might still be useful as a place to start and a guide to explorations.

    Lastly, if you ever do need paint density, it is the easiest of things to calculate - simply weight a 1 oz. container, tare the scale, fill with paint, weigh again - and presto! While only as accurate as your scale and container, it will serve quite well to sort out paints into their major groupings.

    Hope that helps!

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

     

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    I have used a few suppliers of panels with real chalk glue grounds for one-three day workshops that I give and have found them quite affordable. A quick Google search should yield a few suppliers to choose from. Make sure to include genuine, real, or true in your search.

    I cannot recommend painting egg tempera on canvas covered with acrylic gesso. Egg tempera becomes increasingly brittle over time and it should really only be used on a rigid support. However, tubed egg tempera paints are always egg-oil emulsions to my knowledge. These may be slightly more flexible than pure egg tempera. One would really need to preform tests for adhesion and cracking. Even if the tests were positive, I would only suggest painting your tempera very thinly and in a few layers to minimizes brittleness and cracking,

    Acrylic dispersions grounds are generally just not absorbent enough to ensure the adhesion of egg tempera paint. Of course, not all acrylic grounds are the same and you could experiment but I do not have good hope. As above, the egg-oil emulsions in the tubes may fare a bit better, but I doubt it.

    As to purchased panels outside of the boutique genuine glue-chalk grounds, I would you should test some of the better. I would test some of the clayboards as opposed to the panels covered with acrylic “gesso”. I know that some of the suppliers suggest that these acrylic gessoboards are suitable as an egg tempera substrate but this has not been my experience when used with traditional, historical egg tempera techniques. As above, however, you should test to see if any of these fare better with the tubed egg-oil tubed paints.

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    ​Yes unfortunately this is an issue that will continue to plague those who paint in oils/alkyds until more research can be performed. FYI if you enter "zinc" in our search field you will earlier threads where folks have expressed the same concerns. I am sad to state that in conversing with some paint manufacturers recently, percentages of zinc even below 15% in oil paints are showing an increase in brittleness and a propensity for cracking. If you do choose to use paints with zinc in them it is best to stick with rigid supports. I will paste one of my previous responses from one below:"

    But certainly issues have been observed even when zinc white is mixed together in small quantities with titanium or lead (studies performed by Marion Mecklenburg, published in 2008). However, I am also one to state that in conservation we are very prone to basing everything on one single study, which from a scientific standpoint is not always the best approach. This is mostly due to the fact that we have limited resources (meaning funding) as a field. Studies focusing on zinc white need to be repeated in order to truly confirm some of these findings (not that I disagree with them outright by any means). That being said there are really no "best painting practices" alternatives at the moment...until the paint industry and/or conservators and scientists are able and/or willing to perform additional tests we will simply have to wait. For the moment a good rule of thumb regarding zinc white is the less you use the better....but if that is not a good solution you can also simply record your use of zinc white and other materials on the reverse of your painting. This will give future conservators the information they will need when addressing how best to care for your painting should future issues arise (and if your painting is professionally executed and well cared for there may not be any issues!)."

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    ​Very interesting problem....first I would have to state that it is not advisable to use glue/oil/chalk emulsion grounds on flexible supports simply due to the fact that they tend to be too brittle and therefore are prone to developing cracks (a problem that you are already encountering). I am also not sure what "Linseed oil varnish" is....could you perhaps clarify? Does this oil contain a natural resin like dammar or mastic? If so that would certainly make the emulsion ground even more brittle (natural resins are not recommended for use in ground/priming layers due to their inherent brittleness). If you do choose to continue experimenting with these types of grounds on canvas you might look up some recipes that can be found in Kurt Wehlte's book or Max Deorner's text (both references are listed in the downloadable pdf called "Artists' Manuals" that can be found in our Resources section). I myself played around with a recipe from Deorner's text that applied to a reconstruction of a painting by Arthur Dove (again this can be found in our Resources section) on canvas:

    Max Doerner's "Half chalk Ground" or "Tempera Ground":

    "An equal measure of chalk and an equal measure of zinc white are combined with an equal measure of the glue-water mixture (same proportions as used for the sizing layer, 70g:1 liter).  All three components are thoroughly mixed to which 1/3 amount of boiled linseed oil is added.  After this has dried, apply further coats."

    Mind you zinc white is now known to cause potential problems when mixed with drying oils (can cause chalking, brittleness, delamination, etc.) so you might use titanium white instead and/or up the amount of chalk. If you do decide to continue using glue/oil emulsion grounds on canvas please consider possibly mounting your canvas to a rigid support and recording your materials on the reverse of the painting. Both will help promote the longevity of your work!

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    Unfortunately, I cannot give you an authoritative answer but I have asked one of our other moderators to comment.

    In the meantime, here is my unofficial estimation of what is going on. Most likely, this denatured alcohol is 86% ethanol and 8% of another non-consumable solvent (methanol in England but there are other options) which is used as the denaturing component. The aim here is not to make a poor shellac solvent (really the only general use today of denatured alcohol is for shellac and alcohol burners), but to render the solvent unable to be used as an intoxicant. The remainder is likely water.

    I have personally dissolved everything from stick, seed, orange, garnet, and dewaxed blonde shellac in hardware store brand denatured ethanols without problems or precipitation. Shellac is not completely soluble in ethanol of too low a proof resulting in in a turbid, white semi-solution. You can witness the same effect by adding water to a dissolved solution of shellac. The resin will precipitate out of solution when the proportion of ethanol drops too low.

    Baade, Brian

    2017-02-25 20:25:17

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    ​The only rationale that i can see for that advice is either to providve a thicker size layer, or more likely, to minimize the amount of water applied to the panel. It does not seem really necessary to vary the proportion in either scenario. The first could be better accomplished by additional layers and the second would only very slightly reduce the water component. There are reasons to use different strengths of glue for different purposes, but I do not think that this situation calls for it.

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    Yes that sounds about right to me...if you are an "aggressive" worker by nature you might want to be a bit cognizant of that...likewise if you are someone who does not do a whole lot of manual labor (and therefore might need to be a bit more aggressive when sanding)....
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    ​Great question...it really comes down to whether your are interested in Western vs. Eastern techniques as pigments, inks, etc. can be very different (but also similar) not to mentioned specialized. We can advise on some opportunities offered regarding a few topics. Both Natural Pigments and Kremer Pigmente offer courses every now and then that focus on paint making and pigments. Historic RittenhouseTown (Philadelphia) and North Bennet (Boston) offer courses/lectures on papermaking, calligraphy, and bookbinding. Papermaking courses that focus on Eastern techniques are more specialized and often require travel to China, Korea, and Japan (but not always). But as far as immersive "experiences" go, I believe this really requires some lengthy searching online...there may be some courses offered through various college/university programs but again this may involve sending emails to specific fine art departments. At the University of Delaware we do have some courses on these subjects and in some cases students are encouraged to explore their own interests, whether it be reconstructing historic techniques like Fayum painting or organic dye extraction and preparation. There may be some ​courses you might be interested in listed on AIC's wiki here​.​ Hopefully others will weigh in with some helpful suggestions as your interests seem to span a broad range of topics.

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    As long as you put on enough size and ground to adequately cover and coat the fibers sticking up you should be alright. It is preferable not to have a tone of fibers sticking up from the surface but if you coat them sufficiently with sizing and priming it is really no big deal...you really want to diminish that sheen to ensure adequate adhesion.
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    Update: Brian Baade has located a pdf online (their "Synthetic Resins and Varnishes Sheet") from Lascaux that states that their pre-made "Lascaux Fixativ" is 2% B-72 in solution. Whether or not that percentage has changed since the time that this information was put up online is unknown but if it has it probably has not changed drastically.
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    Hi Koo, we see nothing wrong with any of the options you mention. Tests have shown B-72 to be one of the more stable synthetic resins which is why it is a popular material in conservation...but no there is no way at this point to know the ratio of resin to solvent in many of these proprietary sprays at this point but we will double check on that.
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    ​There are always issues with fixatives, especially when used excessively. Too much will greatly darken the media you are spraying it on. Way too much will even make the paper more transparent. You have used them successfully so that does not appear to be an issue. The main issue I would worry about is potential yellowing. Yellowing is probably not a major concern with a very thin application but I would still prefer using a fixative that is composed of a non-yellowing resin. B-72 is a very stable acrylic resin that is not inordinately glossy making it a really good choice for a spray fixative. The problem here is that most manufacturers do not disclose which resin they use. I do know that the product Lascaux Fixative Spray is B-72 in a spray can. I am sure that there are others as well but it is difficult to know for sure. I hope to have a number of the common materials used in art making analyzed in a lab when we secure the funding to enlarge MITRA. I am sure that there are other perfectly serviceable fixatives, but as a conservator this is what I would recommend. I hope that others will respond here with their experiences and favorites.

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    Tyvek is a great material to use for packing, shipping, and storage purposes but the important thing to note here is that it is a very flexible material...while we do not see any potential issues happening between the Tyvek support itself and the acrylic paint here are some things to consider if you are choosing to paint on Tyvek if you want to promote the long-term preservation of your works:
    1) Environmental fluctuations may cause ground and paint layers to expand and/or contract while not affecting the Tyvek support

    2) Accidental creases and planar deformations (should they occur) are often impossible to rectify.

    3) The Tyvek should be mounted on, or positioned against, a solid substrate, framed behind glass/glazing, and stored or displayed in a stable environment.

    4) Tyvek is available in a range of different surfaces with some being more slick while others have a bit of tooth. Try to steer towards the latter, as the surface will provide more mechanical tooth for the paint to adhere to thereby avoiding the potential for flaking and delamination in the future.

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    That should be fine.
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    Aluminum hydroxide or "alumina" has been used as a thickener and stabilizer in oil paint for very long time. It, like aluminum stearat,e creates a gel when dispersed in oil. A very small amount added to an oil paint helps to keep the oil from separating from the pigment, this has been seen as useful, especially for very heavy pigments that want to fall out of the mixture. An excess (beyond what is required to aid is stability) has always been seen as an adulterant. If you buy those really cheap 200 ml tubes of oil paint that sell for 10$ irrespective of the pigment, you are basically getting a tube of aluminum strearate or aluminum hydroxide gelled oil with enough pigment to provide color. This is why student grade paints have a much lower tinting strength than professional grade paints. Aluminum hydroxide is also the primary material in a tube of alizarin crimson or rose matter (this is the substrate that the dye is coordinated onto). Paint these paints out and you will see that their films are rather rubbery and insubstantial. The medium that you mention would is somewhat similar to those touted quite a bit lately composed of a thickened oil and calcite, although I would personally really prefer the calcite/oil mixture as it forms a firmer film with oil than does alumina. I have a tube of a similar medium made by a US company that is 20 years old or so. The residual medium around the tube opening is just as brown as that seen at the opening of an old bottle of drying oil. Additionally, none of these low refractive index fillers (aluminum salts, calcium fillers) mask the yellowing of the oil in the way that many pigments can. I would treat this medium and those like it as if they were slightly leaner painting mediums and limit the proportion so that you create a solid paint film that does not inordinately yellow.
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    Yes it is likely fine to apply a second coat within 24-48 hours, depending on the relative humidity of your working environment of course.
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    Hi Koo In my opinion, the framing and glazing of recent temperas is mostly to protect from physical damage. There are some interesting issues that do result, such as a build of of fatty acid efflorescence on the inside of the glass. In general, placing a work inside of an environmental envelope like a frame with glazing and a backing board will slow down the change in temperature and relative humidity experience by a painting. However, with canvas paintings that live in a humid environment, we suggest that the backing board be vented to allow air flow and to avoid creating a micro environment which may trap moisture and contribute to mold growth. Whether to vent or not vent a backing board may be less of an issue than with canvas paintings due to the panel support, but I am not positive. At the other extreme, museums that lend Old Master tempera paintings routinely have them sealed into a airtight frame/glazing package, sometimes with special materials that regulate relative humidity. This is mostly done to maintain a "safe and stable" environment during travel to minimize expansion and contraction of the panel due to changes in the environment which could cause possible damage. This is, of course, the extreme and an unlikely scenario for a practicing artist. We have sent an email to Dr. Stoner, again, to get her opinion as she is very experienced with framed contemporary egg tempera paintings. Depending on her answer, I may be able to reach out to preventive conservation, framing and exhibition experts for further clarification.
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    I am not sure that the answer is going to be any more exacting than that given on Mark Gottsegen's AMIEN. I do need to ask first, what medium? Anything containing a soft resin should be avoided but if used should be only added in extremely small amounts to minimize paint solubility. The medium recipe would greatly influence how much should be added. A medium containing large amounts of solvent could be added in larger proportions than that containing only oil. Alkyd mediums contain solvents and come in different viscosities. Mixtures of oil and calcite are inherently leaner and could be added in slightly larger amounts. Yellowing and potential wrinkling are related to superfluous oily components. Your procedure does seem like it would minimize the physical amount of glaze on the surface. Certainly the thinner the layer the better and this would go a good way to mitigating negative effects. Minimizing oil is also very important and the crux of your question. I am not sure that you could put an exact percentage on this. There are too many factors. Really, one should use just enough medium to allow one to create the effect one is attempting while also using mechanical means to help thinly distribute the paint. You sound like you are doing this and while I do not know your medium recipe, you appear to be using a sound method. Sorry I could not add anything more precise.
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    ​​Hi - I am sure we can generate that data you need. And just so you know, you can always reach out directly to us at Golden for any of these types of needs. Just in case you felt information like this was not available.

    So, hang in there.....am currently at the College Art Association meeting, where tomorrow I will be moderating a panel discussion on MITRA, so it might take me a few days to format things into a document.

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

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    I am sure you are purchasing and using good quality archival mat boards but it might be worthwhile for you to read over our section regarding archival paper products in our "Flexible Supports" document that can be found in the Resources section. I am assuming you are first toning the surface with the acrylic paint? As far as the gold leaf is concerned you really want to avoid potential formation of corrosion down the line if you are using anything other than 22-24K. If your alloy contains copper and your artwork gets exposed to humid environments or even direct contact with water (lets hope that doesn't happen), the paper-acrylic-size layer beneath your gold will likely react with any copper that is present and could eventually lead to the formation of corrosion products and even flaking. While this could still potentially happen with 22 and 23K, it is less likely to be a problem in the long run.
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    As far as making a PVA dispersion ground this would likely be far more trouble than you would want to undertake, not to mention making such a ground is very difficult to do successfully on one's own. Casein grounds, if used on rigid supports, are fine. You can size the panel just as you might with a traditional RSG ground (actually sizing with a dilute layer of PVA would likely be fine as well). Give it a try and see if you like it...otherwise I would follow Sarah Sand's advice regarding selection and use of good quality acrylic dispersion grounds.
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    It may by OK to speed up the drying of size layers using a fan, although they dry pretty quickly on their own so I am not sure why this is necessary. These are generally very thin in consistency and less likely to have the surface set while underlayers remain fluid and moveable. Even with this I could see the potential for trapping water beneath a coalesced surface film. It is probably OK to apply a second coat of size or even a water born ground after the size feels dry to the touch. I would wait a day before applying an oil or alkyd ground. One should never try to speed up the drying of a ground. This is especially true of natural glue grounds and true gesso which can crack badly if this is attempted. Even with acrylic dispersion grounds, you may get a situation where the surface has dried but the primer beneath is still somewhat fluid.
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    The panels you have already prepped are likely fine....just record that on that back of your painting should any unforeseen issues arise (e.g. note that no sizing was used only priming....). As for the ones you have "over" sanded, you will simply need to add more layers of sizing and priming than you normally would in order to evenly coat everything (again making a note of things on the reverse).
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    Great to get your response and glad you had a chance to read the articles. As to your sense of my wording being 'curious', let me share a few thoughts that may help explain my perspective. One thing to realize is that the first link goes to a presentation from 2010 that looked specifically at 4 paintings done within a very tight timeframe when his approach to canvas preparation was changing and it is true that you get a bit of overlap and combination of approaches. But the middle period I was thinking of came from the much longer stretch of time covered in the second article, which is mostly a summation of a paper Ana presented at the 2012 AIC Conference. That was a presentation I happened to be at and remember the impression it made on me, but unfortunately there is no complete, publicly available copy of that paper I can link to. That said, let me quote from the summary:

    "He painted consistently on unsized cotton duck but his choice of preparatory materials fluctuated over time. Between 1968 and 1973 he used white acrylic gesso and toned it with diluted acrylic.  In some cases he added alkyd.  From 1973 to 1978 he transitioned from white to clear preparatory layers, presumably in order to maintain the raw canvas color and achieve transparencies in his paint layers.  Scientific analysis suggested the clear material was synthetic and consistent with Rhoplex AC-33. This was more or less confirmed by photographic evidence of showing large jugs labeled as Rhoplex located in the artist’s studio.  By 1979 Diebenkorn had returned to using acrylic gesso almost exclusively.​"​

    There is also this Abstract from the Preprints for that year’s AIC Conference as well: http://www.conservation-us.org/docs/default-source/periodicals/psg-postprints-2012-vol25.pdf  (page 29)

    "The analytical work revealed changes in the artist’s materials during the time span of the series. For example, analysis of paintings from 1974 to1979 suggests that Diebenkorn started incorporating clear synthetic preparatory layers in addition to pigmented gessos. This clear layer was confirmed to be Rhoplex AC-33, which was readily available during the time in which the paintings were executed. Cross- sectional and microscopic examination of the paintings also indicated that Diebenkorn prepared a few of his own grounds by mixing clear acrylics with white pigments. Furthermore, by 1979 through the end of the series, analysis suggests that he favored pigmented commercial acrylic gessos almost exclusively. 

    Condition issues in this series were also documented, and a database was created to chronologically track material changes in the paintings and visible areas of instability. Correlations between his choice of painting materials and the general condition of the paintings were noted. In general, paintings that contain layers of brittle alkyd and oil paints over clear synthetic preparatory layers exhibit more severe cracking than those that do not exhibit this layering structure. This observation is illustrated in the database. Pre-1974 paintings tend to be in better condition than some of the mid-series paintings, where unconventional layering structure is observed. Also, when the artist started using commercial pigmented acrylic grounds around 1979, the number of paintings affected by surface cracks diminishes. Painted areas that consist of multiple layers also generally fare worse than areas without heavy layering and reworking."

    So there really was a period when acrylic gesso was essentially phased out and Rhoplex AC-33 took over as the primary sizing material, and that overall the works from this middle period are the ones in much worse shape.​​ Some of the confusion about my wording might be caused by the fact that the works in the 2010 study are from a tight cross section of time during that latter transitional period (1977-79)​ where he is moving from the use of Rhoplex back to just acrylic gesso. So it would not be surprising, I think, to find acrylic gesso being applied directly on top of the Rhoplex in Ocean Park 111 (1978), while the two paintings mentioned as being in good shape (115 & 125 from 1979-80) were commercially primed with acrylic gesso alone and had no Rhoplex at all. 

    Anyway, I ultimately agree with your point, in terms of the main culprit, namely the thick layer of AC-33 with its softness and mobility combined with the brittleness of the commercial alkyds. And really my overarching point is simply that commercial products can bring with them unintended  issues, and that Diebenkorn's use not only of the unadulterated industrial resin AC-33, but also of alkyd housepaints, led to real problems that he clearly did not anticipate.

    I agree that by painting on rigid supports folding and flexibility testing is likely not needed - although even wood supports do expand and contract. And yes, aim for commercial materials of the highest quality if you decide to go there, with price often being a good guide, although keep in mind the story I related in the second post where an artist was using one of the absolute best quality housepaints as a ground, but some of that percieved 'higher quality' for the company and their regular customer was the touted stain and dirt resistance, which led to the adhesion problems. Just realize that commercial paint companies are aiming for a different market with different expectations of service life and longevity, and that even a basic acrylic paint is a balancing act of some 15 ingredients and chemicals that can all cause their own issues. 

    One last thought - if going commercial for a primer, have you thought about Zinsser's B-I-N, a pigmented white shellac? I ask not because I think it escapes all the issues and problems, but it has the distinct advantage of being a much more simple and basic paint with fewer moving parts and unknowns.​

    Sands, Sarah​

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    ​We have some information about this in our "Rigid Supports" document that can be found in the resources section that I will include below. As for sanding too much, it is not the end of the world to have a few fibers sticking up here and there...try to lightly sand those areas down if you can because they can cause skips and breaks in the sizing/ground layer(s) during application. As for health and safety precautions you should always wear an appropriate face mask and goggles when you sand anything. You can find additional information on this topic in our "Health and Safety" document in the resources section. If you do go with a belt sander just be careful that you do not over sand as it is very easy to do so rather than sanding by hand (you will have more control with the latter even though it is more arduous). 

    "Degrease the surface with denatured alcohol before applying layers of size, ground, and/or paint. Without this preparation, ground layers may not adhere to the smooth side of these supports because of surface resides such as paraffin wax that may be left during the manufacturing process. • Gently sand the face of the panel with fine sandpaper (e.g. 220 grit) to provide a slight mechanical tooth but be careful to not overly roughen the surface and unevenly expose the wood fibers. This can lead to irregular swelling of the substrate (particularly when water-based sizes, sealants and/or priming/ground are applied).​"

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    This is covered a bit in our "Rigid Supports" document that is located in the resources section so I will copy an