MITRA Forum Question Details

​This is very complicated and it is not as simple as is often stated. I promise to post a reply in the next couple of days. I also want to have a few other experts weigh in.

​Here is the 1st response from Robert Gamblin.

So I wanted to check that the 6 claims I am about to make in my article on creating permanent paintings are accurate. These are the very short summaries.

• A rigid support is better than a flexible surface

In general I think yes, though we all know that many stretched canvases age marvelously well,  rigid supports will move less than flexible whether it be in response to changes in atmospheric moisture, movement during moving the painting from place to place, and insures that the back of the painting is protected.

• Alla Prima is better than layers

The universe of ways of making a painting are so varied that one can’t make this statement with confidence.  e.g. what if the alla prima paint is like so many colors from the tube today, nearly under bound, which leads to a less flexible paint film than one with a good amount of binder.  

To make this statement also tends to suggest that a way of making a painting is superior to another. When what is primary is that the artist realize his/her/they vision.  In order to do that, for some it will be an alla prima painting, and for another it will be 40 thin layers of glaze in an alkyd medium of one transparent color, etc. ad infinitum.   I see our job as helping artists to realize their vision and not to make a painting with the fewest cracks.

• A thin layer is better than a thick layer

It depends, first, what is a thick layer?  What is a thin layer?  What is used to make the layer thin? A material that will make the layer more flexible, or more brittle?  Does the thick layer have anything else in it?  

• Use oil paint with fewer ingredients

History does seem to suggest that simpler is better. 

• Add few or no mediums

Again it depends, my belief is that oil colors today are much more loaded than they were in previous periods, by definition this means that 

from-the-tube oil colors are less flexible than in previous periods, BUT an enormous amount of painting mediums are made, purchased and used today, this addition of medium to the tube color most likely puts the oil/pigment ratio of what goes on the surface today similar to all other periods.  

Paint has to come off the brush in just the way the artist wants, color is either made to do that specifically for the artist or as today, the artist adjusts the viscosity themselves. 

• Varnish after 6-12 months

Not a bad idea, but if the painting is going out the door a few weeks after it has dried, and the artist will never see the painting again, I think one can varnish with the new synthetic resin varnishes we have today without fear….that means varnish thinly, as one should anyway.  

Notes by Robert Gamblin

Otis, Oregon 12/18/21

These types of answers are often written in such a way as to be ambiguous at best. A rigid support is better that a fabric support…unless that rigid support is a sheet of iron vs a linen canvas well sized and covered with a high-quality acrylic dispersion ground or a lead white oil ground. This is the exaggeration of the discrepancy but not really to a great degree.

I do not sign on to the notion that ALL rigid supports are superior.  I have major issues with hardboards and MDF, not because of their responses to humidity, but mainly as to how they respond to physical impacts. As a conservator, it is extremely difficult to deal with a panting on hardboard that has been impacted on a corner. The expansion of fibers is almost impossible to rectify. However, this problem can be made less of an issue if the work is framed by a medium less likely to become deformed if it is struck on the corner. Hardwood framing would go a long way to remedy this problem.

This is such a huge topic that I am not even going to attempt to be comprehensive here. There are so many issues that contribute to the visual perception of condition within the museum sector.  1. Canvas paintings are easier to restore and make look undamaged. 2. Panel paintings in the UK and US were generally taken from relatively stable RH environments and brought to places where the RH varied vastly over the day, weeks, and years. Often varying as much as 50 % in a day. This caused real damage. 3. Most panel paintings brought to these regions were thinned to about 1 cm and had a cradle attached to the reverse. This has turned out to be disastrous, causing massive damage over time. I am not interested in going through the entire history of the travesty of panel painting conservation here but please understand that the issue is more complicated than one would think.

When I write about rigid supports, I expect a relatively innert support that does not greatly expand or contract with changes in temperature and RH. I also hope for a material that has sufficient “tooth” or a least an affinity, for any subsequent layer or ground so that there is not a source of possible later delamination. I would prefer a textured inter-layer to adhere to the substrate, or sized substrate if necessary, so as to allow for a physical grip to the substrate. This layer is not necessary if one chooses the optimal substrate and ground.  I would then like an appropriate ground.  This could range from a high-quality acrylic dispersion ground to a lead white oil ground depending on your needs. There is a lot of wiggle room afforded by the above.

There is so much more to discuss about these subjects, and I have only hit on the bare minimum of the possible answers.

​​​As the egg tempera moderator, I feel compelled to note that, while the paintings examined ranged from 150-650 years old (which would place some in the late 1300s, when the majority of panel paintings were egg tempera), the only medium specifically named is oil.  I'm curious – among the oldest paintings studied, were any egg tempera?

Of course, oil painting is much more popular with and its issues more relevant to modern day painters; contemporary egg tempera painters are a teeny tiny fraction of working artists.  This is in part (perhaps largely) due to the demands of making paint from scratch (initially a challenge, but becomes less so with experience), as well as other unique properties of egg tempera.  However I also believe it's because tempera is so often neglected in discussions/writings about mediums; consequently few people even know of its existence, or that many beloved late gothic & early Renaissance paintings are mostly egg temperas, never mind the medium's unique characteristics.  Among the millions of oil painters out there, I can guarantee (having had them as students) there are some (many?) waiting to discover a medium that better suits them - such as egg tempera – if only there was more discussion of it.

So, it may be nitpicking, but it think it could be helpful when asking about “best practices" to specify clearly which medium one is trying to figure out best practices for (instead of presuming by default that the medium is oil).   Perhaps it would be helpful, in your article, to write something along the lines of, “I want to check 6 claims on creating permanent oil paintings".   

Apologies if this sounds persnickety. I am content (in fact, I like) egg tempera's small orbit.  However I see many presumptions/facts about oil transposed to egg tempera that aren't true or helpful to understanding egg tempera, precisely because statements that seem to be about painting generally are actually about a specific medium.    

I affirm Marc and Brian's comment on the incredible complexity of this topic. I've received many emails from tempera artist (some well-established) where something has gone wrong with a painting, asking for a diagnosis.  But there are so very many variables that go into the creation and subsequent existence of a painting that, without knowing every detail, it's hard (impossible?) to say what went wrong.  Generally, the more complex a system, the more that can go wrong, and the harder problems are to properly diagnose - yet this generalization isn't helpful or correct for every situation, as Marc and Brian note.   

Still, I appreciate the questioner's goal of clarifying best practices, to the extent possible.

Koo Schadler

Rigid supports are preferable to canvas unless the size is so large that weight becomes a consideration.  Then canvas mounted to a strainer

with a backing board is a good alternative.

Multilayer paintings show no greater inherent vice than alla prima when reviewing conservation records if the painting is executed in stages with no questionable materials or techniques.  However, applying intermediate varnish layers or violating fat over lean and using disputable mediums is shown to create a bulk of the problems.  This also calls to question why do artists feel the need to oil out a surface before adding another layer of paint. 

Thin layers are safer due to the way oil paint initiates the drying process.  Thick layers trap paint deep inside that take a long time to cross link.

Simple is better.

Mediums:  All things in moderation.  However, many techniques demand thin paint that does not match the viscosity of the paint that comes straight out of the tube.  Also mediums need to be carefully selected.  Encouraging use of mediums does not include the use of Maroger  medium.

My gut agrees with the varnishing statement of not having to wait 6-12 months but it is not supported by the physics of the way drying oils actually behave in the real world.  Thick paints is very slow to dry.  It would be worth setting up a test to see if measurable thick paint is not harmed by applying a thin synthetic varnish layer a few weeks after thick paint is dry to the touch. Will it wrinkle or not?

Respectfully,

Michael Skalka

Chair ASTM Do1.57

​​​Hi Julie,

Yes, I know you put oil in the title of the post, and I didn't mean to nickpick the post.  I've just read many articles, invariably centered around oil, that don't clearly distinquish the medium being discussed.  So I wanted to clarify that when you mention "permanent paintings", as you do a couple of times, it would be helfpul in an article to say "permanent oil paintings" - as you actually do in​ the full title of the article, noted in your last post.

I agree that people don't necessarily presume the word "painting" refers to "oil"; what I meant to say is that I see writers discuss principles specific to oil painting, yet don't clearly specify the medium is oil - so less expereinced readers sometimes presume those principles apply to painting generally, including egg tempera. This happens a lot with students and online forums.  Again, if I sound chippy about this, I don't mean to; many mediums are not well understand...but there is just so much misinformation about tempera and much of the confusion derives from oil characteristics transposed to tempera.  ​You have experience and can distinguish between the two mediums, but many people can't.  So I'm glad to read your clear and specific title.   

Thanks for the discussion.  Koo