MITRA Forum Question Details

​Thanks for your replies.  I take your point, George, about  needing to know ingredients for a more carefuly controlled Test Panel 4, so I'll use the Rublev Fluid Medium (VAE) as a base.  And I'll add barite to my list of additives. 

Brian, last year I had good success tarnishing a drawing by laying the panel face down over a tray of liver of sulphur - it seemed to work very well, very quickly.  So I'm going to repeat the experiment, using a slightly more contained set up, and then do the same with garlic and onions.   

My testing is far from technically refined - I don't have training how to do so, my time is limited (I'm supposed to be painting, after all!), and I rarely have enough time to do repeat trials - so results are far from conclusive.  Nonetheless, it's fun and instructive to play and better understand these old and/or less common mediums. 

Pewter (mostly tin and anitmony, I believe) draws beautifully, if you can find a rod (I lucked out with a pewtersmith friend). I've found bismuth, zinc and bronze points, and just ordered a lump of antimony too.  

Koo

Hi Koo,

Thanks for pointing me to this forum. I've done a lot of the tests you're involved with, and can answer some of your questions.

Test Panel 1: Surprisingly, gold is a soft metal but draws light, and silver draws darker. Pewter makes a nice dark mark, as will bismuth. (a) Generally the thicker the ground the darker the mark; with that said, some aqueous grounds like RSG and Gouache will chip if there are too many coats. I've found a sweet spot with three coats of well-cured casein, sanded with 800-grit to increase smoothness. (b) By age do you mean tarnish? Materials in the ground can also affect the cast of metals, such as gold appearing more amber on zinc white than on titanium. Other than tarnish, there is the chance that metals will react with the groud - magnesium for instance utterly disappeared from Golden Silverpoint Drawing ground; it just evaporated. By comparison, magnesium remained visible, but lightened substantially when applied to white casein. Other than that, the ground and paper constituents can affect tarnish both in degree and rapidity. Sulfite papers can hasten tarnish, as can other substrates, like TerraSkin.

Test Panel 2: Also try different shaped points! Fine, blunt, etc. If you know a metalsmith order a bismuth ingot and have it cast into a rod. It has a low melting point. Zinc is available as wire from Amazon (or call me, I can share).

Test Panel 3: Add egg yolk to your liquid prep, lots of sulfur in egg. Also: humidity increases tarnish. Watch out for Liver of Sulfur - it can raise the pH of paper and make it yellow.

Test Panel 4: All good fillers, but I have found, over the years, that a pure Zinc Oxide and binder ground works best; no fillers needed. I think abrasives like bone ash benefit from a half hour of mulling in the mortar and pestle; they can be uneven in their particulate makeup.

Tom Mazzullo

​Brian, I agree - casein has always for me hastened tarnish over more inert binders like RSG. Some commercial caseins also have a lot of linseed oil as a preservative which necessitates a long cure time; I wonder if the off-gassing is mitigated by open-air curing of a week or more before use. One would need some gnarly equipment to measure things like that, would be fun to know.

Hello All,

I appreciate everyone's comments.  Thanks to Tom Mazzullo, an experienced metalpoint artist, for writing in -  your expertise is appreciated, Tom.

I concluded several experiments and have results to share.  To clarify, I'm not scientifically trained & can't say variables were perfectly controlled or results replicable.  Still, there are things to note.  Pardon the considerable text!  I did edit but there were 4 tests and a lot to describe.  Brian, feel free to edit if it's inappropriate to mention specific products.  New questions from me appear in bold. All comments welcome. 

TEST PANEL 1 - Grounds

I tested 17 grounds (3 animal glue, 2 casein, 1 gouache, 9 synthetic polymers, plike and terraskin papers) by marking each with 12 metal nibs (hardness Mohs 1.5 to 4).  My criteria for a good ground were: (1) Capable of being smoothed (sandable), so nib doesn't skip and mark making is consistent; (2) capable of creating relatively dark marks.

- All grounds performed well enough to recommend, although some were clearly better than others.

- I preferred a solid support and multi-layered ground that can be sanded and allows for working the surface during the drawing process.  As Tom noted, multi-layered grounds were prone to chipping.  I think working on a rigid support (I used MDF) and good surface preparations (wiping panel with alcohol, then roughing up surface before application of ground) can help to counter this.   

            Any thoughts on how to discourage chipping?

- I tried 9 polymer-based grounds.  The more polymer in a ground = less prone to chipping but more difficult to sand, and less hard/resistant surface = less dark marks.   The more pigment/filler in a ground = more prone to chippingbut easier to sand, and harder/more resistant surface = darker marks.   It was a tradeoff. 

-  Gouache & Casein were good grounds but difficult to develop a sufficiently thick coating to sand to ideal smoothness.  I don't like the feel of paper fibers coming through (but some artists may).  Pelikan Plaka casein did allow for multiple layers, but final surface didn't feel sufficiently resistant; however I cured it for only 2 days before drawing.

           Tom, when you say you draw on "well-cured" casein, how long is your cure time?  Does the casein become noticeably harder, more resistant?  I couldn't find ingredients for Pelikan Casein – does it contains oil?  Why is oil added to casein?

- I too saw the effect mentioned by Tom and Brian:  The color of a metal point is visibly (sometimes dramatically) affected (appears more or less colorful) depending on the ground to which it's applied.  I suppose there are too many variables to say precisely why this is so, but it's an important consideration for metalpoint artists.

- Black Gesso was sandable and takes metalpoint very well. Metal nibs on black ground yield more distinctly colored marks reflective of the metal.

- If an artists wants to later color a drawing, an insoluble (synthetic polymer-based) ground may be preferred so that applications of watercolor, gouache or egg tempera won't rewet and disturb the underlying ground and metalpoint marks.   

            Any thoughts on the challenge of coloring a drawing using water-based paints atop water-soluble (animal glue or gouache) grounds? How long does casein need to cure to be insoluble to water?

TEST PANEL 2 - Different Metals

To a single ground I applied different metals: lead, lead-tin, tin, bismuth, antimony, pewter, zinc, pure silver, sterling silver, argentium silver, gold (22K, 18K, 14K), aluminum, bronze, copper, yellow brass, red brass, nickel, platinum.

I used fine and blunt points, thin wires and thick rods, rough chunks of metal (i.e. a block of antimony ordered from China for $2).  The variety was extensive and fun.    

- Metals with Mohs 2 hardness or less aren't easily worked with a fine point, the tip too readily bends. You either need a fat stylus that can stand up to pressure or, if using a fine stylus, have to continually re-straightening the tip of soft metals. 

- Some metals aren't readily available as wire or rod; you have to find a smith willing to melt and shape the metal for you (as I did for pewter and bismuth).  

            Thanks, Tom, for your generous offer to share resources.  I found everything I initially planned for.  I haven't yet tried magnesium; is it worthwhile?  Any other metal possibilities?

TEST PANEL 3 - Abrasive Additives 

I added 20% of each additive (listed below) to a polymer-based gesso; sanded smooth; then drew with 5 nibs (pewter, gold, silver copper, brass).  Additives were: Marble Dust, Gypsum, Silica, Glass Powder, Bone Ash, Barite, Talc, Pumice, Titanium White, Zinc White, Large micron size historical pigments (Green Earth, Yellow Ocher, Diptasio, Lazurite, Malachite).

- All additives increased abrasion to some degree (a little to a lot) resulting in darker (to varying degrees) marks.  

-  Adding too much of an abrasive (above approx. 20%) made ground more vulnerable to chipping. 

- Large micron-sized, historical pigments had the least effect, a barely perceptible change in darkness.  They made the surface rough and irregular = less consistent marks.  Overall historical pigments were not agood strategy to improve mark making.

- Best results (darkest marks) obtained with Silica and Pumice. Given their high Mohs hardness (7 and 6 respectively) seems hardness of additive more effective than particle size in abrading metal nibs.  Bone ash, titanium and zinc also worked well to enhance marks.

- Silica and pumice also notably enhanced metal colors (a beautiful effect).  When silica or pumice was added to a ground, the distinct colors of gold, copper and brass nibs were much more apparent, almost an iridescdent quality.   Pumice created the most pronounced effect.  

            Why did silica & pumice bring out the color of metal nibs?  Given their hardness, more metal is abraded, but titanium white and glass also are very hard and, while they made darker marks, they didn't make more colorful marks.  Any ideas?  Perhaps something to do with the structure of silica and pumice, how light is scattered?  

- I figured talc and gypsum, given their Mohs number (lower than most metal nibs), would not increase darkness of marks; but they did, albeit minimally.  Don't understand why so I'd like to replicate this test, to be sure. 

TEST PANEL 4 - Tarnish Test Panels

I tested 7 grounds (Plike paper, Rublev Tempera Ground, Artboards Ground, Pelikan Casein, Gouache, Rublev Silverpoint Ground, Black Gesso).  Each ground was marked with 8 metal nibs (Bismuth, Zinc, 14 K Gold, 24 K Gold, Pure Silver, Sterling Silver, Brass, Copper).

I made seven identical panels, with Panel 1 a Control panel (not exposed to tarnishing substance).  Other panels subjected to six tarnishing environments (Panel 2 = Cardboard box [not airtight] with open jar of liver of sulphur; Panel 3 = Sealed glass container with open jar of liver of sulphur; Panel 4 = Sealed glass container with liver of sulphur at bottom, test panel directly over sulphur; Panel 5 = Sealed glass container with chopped onion; Panel 6 = Sealed glass container with chopped garlic; Panel 7 = Sealed glass container with open jar of apple cider vinegar.)  Panels were scanned after 24, 48 and 72 hours of exposure to tarnishing environment.  

- Small changes created very different results.  For example, garlic fumes turned bismuth on Rublev Silverpoint Ground (but no other ground) an orangey color, whereas onion fumes did not.   With so many  variables, results are hard to summarize. 

- All environments sped up tarnishing to varying degrees.  Panel 4 (directly over Liver of Sulphur) and Panel 7 (apple cider vinegar) tarnished fastest.

- All environments more or less degraded marks after 72 hours.  Panel 7 (apple cider vinegar) completely erased zinc after 48 hours, and erased bismuth, brass and copper on some grounds in 72 hours.  Direct exposure to Liver of Sulphur erased some metals in72 hours.  

            I thought a layer of tarnish protects the underlying metal from further corrosion.  If so, why do some metalpoint marks disappear after too much exposure to a tarnishing environment?   Is it because a metal mark is so thin there is only a degraded tarnish layer, which falls apart?  Or is the ground (and hence it's ability to hold onto metal particles) being degraded? Or both?  What literally happens to metal marks that vanish? I realize these are complicated questions that perhaps can't be answered; I'm just looking to better understand metals, tarnishing, corrosion.   

- Some grounds held onto to marks better (Artboards Gesso, Gouache, Rublev Silverpoint Ground, Rublev Tempera Ground).  Pelikan casein lost the most marks.  

- Some metals seemed more vulnerable to corrosion and disappearing; Zinc and 24K gold in particular.

- As Tom and Brian have already noted, degree of tarnishing and coloration of a metal varied (sometimes greatly) depending on ground.  One example: Artboards Gesso and Rublev Silverpoint Grounds visibly brought out blue in zinc, other grounds did not. There were many such  diferences among the various grounds and metals.  

            Tom mentioned humidity speeds up tarnishing.  Why is this so?  More exposure to oxygen (which, from what I understand, is the primary agent of tarnishing)? 

            Regarding adding egg yolk (sulphur) to liquid prep to increase tarnishing – Tom, do you mean mix yolk directly into a ground?  Are there considerations to adding egg yolk to various binders (animal glue, casein, gum arabic, synthetic polymers)?

Brian, I know MITRA isn't a promotional site, so please edit if it's not appropriate to mention that Tom Mazzullo and Susan Schwalb's have a newly published metalpoint book. I'm looking forward to reading it, which hopefully will make a dent in my many questions.  Thanks for everyone's input and help.

Koo

Any thoughts on how to discourage chipping?

I've found that with aqueous paints, applying the subsequent layer while the previous layer is still evaporating (cool to the touch) allows the layers to bond more fully, and chipping is reduced. Applying a new layer over a dry underlayer for some reason sometimes causes the top layer to flake off, even if the underlayer is sanded. I apply two layers, the second layer goes on while the first is still damp but not obviously wet. This is tricky because with too-vigorous application of the new layer, the underlayer can dissolve. In each subsequent layer for that reason I add a little more water to the prep for smoother flow. I sand the top layer after the casein is dry and has had time to cure.

Tom, when you say you draw on "well-cured" casein, how long is your cure time?  Does the casein become noticeably harder, more resistant?  I couldn't find ingredients for Pelikan Casein – does it contains oil?  Why is oil added to casein?

Minimum 24 hours, ideally a week. It depends on the casein – Plaka: 24 hours (or dried in a warm turned-off oven!); Shiva: 48 hours or more, Homemade (emulsion and pigment): 24 - 48 hours or more; Wrights of Lymm: a week; Sinopia: weeks (Sinopia has more linseed oil than it needs).

Casein becomes harder and more waterproof after curing; meaning it dents with a blind stylus when it is only a day dry, and can be removed with vigorous wiping with water (handy).

I have no idea what precisely Pelikan Plaka contains, but all commercial casein contains some preservative, usually linseed oil to create an emulsion. Without oil casein has a shelf life of a few days at most because it is made from milk protein turned into a type of glue with an alkali reaction. You can make casein yourself with cottage cheese and borax! It will spoil in a few days and your house will smell terrible even longer.

Any thoughts on the challenge of coloring a drawing using water-based paints atop water-soluble (animal glue or gouache) grounds? How long does casein need to cure to be insoluble to water?

I think with a light touch watercolor over soluble grounds is do-able. If you scrub like Homer you'll dissolve the ground eventually. I would rather use pastel applied to a soft-hair brush for coloring an RSG or Gouache ground. 

Casein is a different animal – after curing a week you can be assured that a well-worked application of aqueous paint over a drawing on casein prep will leave the ground intact. I have done drawings with metalpoint on medium-toned casein ground then applied Chinese White over the drawing for a chiaroscuro effect, only to regret adding the highlights; I then completely removed the Chinese white by scrubbing it away with a soft brush dipped in clean water, then blotting. Neither the drawing nor the ground was not disturbed. Chapter 5 in our book may answer some of these issues, it's all about mixed media!

Thanks, Tom, for your generous offer to share resources.  I found everything I initially planned for.  I haven't yet tried magnesium; is it worthwhile?  Any other metal possibilities?

Magnesium is highly reactive, and completely disappeared from a gesso ground within days of application. It did better on RSG/Zinc white (more inert?) ground, but faded substantially. Avoid it for anything but a gimmick.

I have been using Palladium extensively for soft shadows. It is a very light-drawing metal and retains its luster when compared to silver, creating an interesting warm/cool effect. I also got hooked on Argentium Sterling silver because it is wonderfully soft. Argentium is an alloy of silver with Germanium, designed to resist tarnish, and the combination of Argentium and Palladium is nice, the lusters are very compatible.

Why did silica & pumice bring out the color of metal nibs?  Given their hardness, more metal is abraded, but titanium white and glass also are very hard and, while they made darker marks, they didn't make more colorful marks.  Any ideas?  Perhaps something to do with the structure of silica and pumice, how light is scattered?

Perhaps. I think that pigments are reactive with metals, but silica and pumice are more inert. Like the difference between making tomato sauce in an enamel vs. plain cast iron pot: the pan affects the flavor. For example, Zinc Oxide white  tends to allow gold to look characteristically ochre, but Titanium Dioxide white for some reason robs gold of its luster. Similar things happen when metalpoint preps have copper-based pigments added, such as Phthalocyanine blues and greens.

I thought a layer of tarnish protects the underlying metal from further corrosion.  If so, why do some metalpoint marks disappear after too much exposure to a tarnishing environment?   Is it because a metal mark is so thin there is only a degraded tarnish layer, which falls apart?  Or is the ground (and hence it's ability to hold onto metal particles) being degraded? Or both?  What literally happens to metal marks that vanish? I realize these are complicated questions that perhaps can't be answered; I'm just looking to better understand metals, tarnishing, corrosion. 

It does for sure on a large metal object like a spoon, but many things affect these atom-thin metal marks in our drawings. Paper quality, ground composition, air quality. Metal is reactive, and dissolves in a caustic environment. I think the metal literally becomes part of the atmosphere, reacting with ions in the air, becoming a new compound and being carried away by airflow. Under normal care, I doubt the ground is giving way. The drawing process presses metal into the ground, and it should stay there unless abraded. I would love to hear a chemist talk about silver sulfide, reactivity of copper in sterling silver alloy, etc.

Tom mentioned humidity speeds up tarnishing.  Why is this so?  More exposure to oxygen (which, from what I understand, is the primary agent of tarnishing)?

The air is denser, and its particulate composition would be too. Come to Denver. Thin, clean air and no tarnish on silverpoints unless one monkeys with the ground. And not oxygen for silver - sulfur! Silver sulfide is the primary tarnish compound we would see. Oxidation is a bit of a misnomer for tarnish.

Regarding adding egg yolk (sulphur) to liquid prep to increase tarnishing – Tom, do you mean mix yolk directly into a ground?  Are there considerations to adding egg yolk to various binders (animal glue, casein, gum arabic, synthetic polymers)?

I do. A squeeze of half an eyedropper into two ounces of liquid prep will aid in tarnish, as well as create a more solid, hard, smooth surface for drawing. The only consideration is that adding too much yolk can destabilize the ground, causing it to flake. Too much also creates a glossy ground. A little does the trick. I wouldn't add it to acrylic emulsion though. Or maybe I would. That's something I have to test.

Best, Tom M.

Now I understand about commerically produced casein; it's like commerical egg tempera in that a bit of oil must be added to make the ET tube-able, whereas egg tempera from scratch doesn't need oil (but lasts for only a day, or a few, if refrigerated - and when it goes bad, may smell even worse than old casein).  

Thanks for the Palladium recommendation, I will give it a try.  I see Rio Grande offers it in wire form - any other suppliers you'd suggest?

I too would love to hear a chemist talk about silver sulfide, reactivity of copper in sterling silver alloy, etc (hint to any chemists who might be listening). 

And don't tell the conservators, but I've done the oven trick myself (we are very bad, I know).  You've shared a ton of very useful, esoteric information - thanks a million Tom. 

Koo

​I need to correct: in my third answer, above, I write, "Neither the drawing nor the ground was not disturbed", I meant to say, "Neither the drawing nor the ground was disturbed". 

I'm glad to know an oven isn't reprehensible, as the point truly is to make durable paintings.  To be clear (rather than glib) I always heat the oven to the desired temp, then turn it off (given how easy it is to get distracted) before I put in artwork.  

It seems copper, zinc, brass, many alloys are reactive with ammonia if moisture is present, so good to know that ammonia may be added to casein.  It seems there are oodles of variables, many of which may be unknown/ unaccounted for, that can affect tarnishing.

Koo

​My experience with casein has been that the most stable artist casein paints are made with borax, giving them a longer shelf life than those paints made with ammonium carbonate. Is this the ammonia that's being discussed? The idea of adding ammonia to casein paint to improve it's shelf life is new to me. Is there a source for reading about commercially-made artist's caseins having ammonia as an additive? I do know that linseed oil is used in casein paint both as a preservative and to make a waterproof emulsion.