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I have read many times where people have made statements about the durability of paint films. Statements such as linseed oil produces the most durable oil paint film, or that slower drying paints tend to form softer weaker films, or that additives like clove oil, resins or other additives can make a less durable paint film.
My question, is what does that actually mean in practice? Are differences in durability in a paint film measurable by a microscope, or other chemical or other scanning tests? Are differences only apparent in bending tests, or do they relate to delamination in real world paintings.
Does a 'less durable' paint film mean it is more likely to delaminate, or that it will withstand less stress and strain? Will a painting done in linseed oil on dibond last longer before cracking than the same painting if done in say safflower oil? Or is there no appreciable difference?
I realise these are impossible questions, but I hope you can feel my frustrations about the lack of answers regarding what a 'less durable' paint film actually means..
Move this whole section up, swapping places with the section above it.
I am going to let those who are involved in the paint
industry provide a more concrete answer but I would like to point out that paint
film durability involves more than bending, shearing, and delamination. There is
also brittleness, resistance to UV deterioration, resistance to physical
abrasion, and solvent/chemical sensitivity.
Thank you Brian,
Actually doesn't your explanation of all the different attributes suggest that 'durable' is too simple a word to describe the differences between paint films?
When the word "durable" is used relating to oil paint vehicles, in my opinion it means that the material forms a film that retains strength, flexibility and adhesive power indefinitely. "Durable" also means that works of art made using that material can be displayed, stored and maintained with ordinary care.
A good oil painting vehicle derives strength from molecular bonds in fatty acids that make up the material. The bonds that lend strength can also affect neutrality of color, but fortunately, we have options like poppy, safflower and walnut oil which, while not the equal of linseed, are still suitable for permanent art.
The comparative advantages of different vegetable oils as paint vehicles have been studied for a long time. Paint chemists do understand the mechanisms behind the forming of films, how those mechanisms are affected by catalytic driers and anti-oxidant retarders, and can make objective judgements based on that science. (I'm not a paint chemist myself, btw.)
Your frustration is understandable and I don't know that I have any clear, singular set of definitions that will resolve things. I think a lot of the problems occur when one moves from very targeted, focused research, where terms and test parameters can be defined, to broader statements that we all fall into the habit of using as a form of shorthand. Just to give a couple quick examples. If you had some paint and asked us to test its durability, that could refer to so many things we would need to know what you were concerned about before beginning. Flexibility? Weather and heat resistance? Solvent sensitivity? Mar resistance? Gloss retention? Surface hardness? And then under what conditions, for how long, after what amount of time, applied in such and such a way, and on and on. Or take when someone says something is non-yellowing. In truth, everything yellows – the question is always how much over what period of time and under what conditions. But because it can get tiring to spell out all those caveats, at some point we all fall into the trap of saying this or that material is "non-yellowing", even though that is invariably not true except within a narrow set of parameters and qualifications.
In terms of your specific questions, durability can be tested in the lab if the specific properties are well defined. So we can definitely compare how much a paint film will stretch or bend, how solvent resistant it is, or how hard or soft the surface becomes. I think the problem you are pointing to, however, is when we then make the leap from those test results out to specific outcomes in paintings. And that is definitely up for argument and debate. At a recent conservation conference I attended, a well-regarded researcher challenged the importance of certain test results by reminding people that cast paint films are not paintings. And that is indeed true. On the other hand, we need to make choices; as imperfect as the results might be, you still need to place your bets on something. So, you weigh the evidence as best you can, based on the research, and choose what you think has the best shot of lasting. Because that invariable leaves a bit of uncertainty, some people are tempted to eschew everything modern and stick only with "time tested" materials or techniques. But that has its own pitfalls and what we know about the past keeps changing. Also, keep in mind that at some point all of those past materials and techniques were NOT time tested – the artists then, as now, were taking leaps of faith using the best knowledge they had to make educated guesses about permanence.
On the third set of questions, durability and adhesion are different things. Or at least I think of them that way. A paint film has cohesive and adhesive properties – cohesive referring to its internal properties, its inner strength or what holds it together, while the adhesive speaking to the strength of the bonds it forms with another material. So you can definitely have a durable paint film that delaminates. And a film that cracks might still be well adhered to the underlying layer. Stress-strain of a cast paint film is only a measure of that material's individual physical properties, so in a way speaks to cohesive forces and durability in isolation. But researchers that look at paintings as a complex laminate, or sandwich of differing layers with differing attributes – such as Marion Mecklenburg - have shown that these individual properties impact and interact with each other in complex ways and that these can be modeled and used as a way to understand specific defects seen in actual cases. But even here there are debates and unsettled questions. That continual mess in the muddle of it all.
Okay, I will leave it there. As you can see, no clean answers. I wish there were.
Thank you all for your help. Especially Sarah for writing that comprehensive and useful Essay :)
I can imagine that the timescale involved is what makes it harder to test these things as well. Let's paint a pigment in a certain percentage of linseed oil on Dibond, now do the same with the oil being Safflower, or Walnut. Ok, now let's see how long it takes to crack. Hmm. decades, centuries did you say?
Well I end up getting tied up in knots worring about archival concerns.