There is an article at naturalpigments.com by George O'Hanlon called „Painting for Posterity with Modern Oil Paints", about some aspects of oil painting. I'm posting a question about it here, because „Forum" section at naturalpigments.com hasn't been functioning for some time (or it seems that way - not possible to start a new topic) and also because George sometimes posts also here. I'd like to know his opinion – but of course everyone is welcomed to share their knowledge and experience.
Quoting from the article:
Fat-Over-Lean Rule
You are probably familiar with the fat-over-lean rule. What the fat-over-lean rule implies is flexible over less flexible paint layers. When you apply a more flexible layer on top of another, the final paint film will be more resilient and more resistant to cracking. Increasing flexibility is accomplished by adding more medium or oil, or lowering the pigment volume concentration of the paint with each succeeding paint layer.
However, this is typically difficult to achieve in practice. Most artists don't understand what constitutes fat or what is lean. It is impractical to measure the ratio of pigment and binder while painting. What I will tell you next may sound like heresy but you do not need the follow this rule if you use paint at its CPVC, which is applying paint straight from the tube, and paint thinly. On the other hand, working in thick paint layers and/or with lots of medium or oil added to paint requires one to observe the fat-over-lean rule.
I visit mitra forums from time to time and there already has been discussion about fat over lean, and so far, the conclusion was, that in fact every paint is formulated to be lean out of tube (i.e. made with just neccesary amount of oil, at CPVC or so).
The statement of my interest is : „(…) you do not need the follow this rule if you use paint at its CPVC, which is applying paint straight from the tube, and paint thinly." It is not clear, George was reffering to Rublev colors or any oil paint in general. And that makes me wonder; whether he meant paints based on various pigments in same oil, or in various oils as well.
You see, there are manufacturers like Williamsburg, Gamblin, Michael Harding and of course Natural pigments, who use linseed oil as a default binder for their entire line of oil paints and they also offer some pigments ground also in other oils like walnut or safflower. If one wants to use only linseed oil based paints, it is possible with these brands. But on the other hand there are many manufacturers who use different oils or oil blends for different types of pigments. One example I can mention is Blockx; they use linseed oil for iron oxides, natural earths, blacks and few other pigments (e.g. PY53, PY154, PY184) or blends (e.g. Paynes Gray, Indigo) and poppy oil for everything else, i.e. blues (organic and inorganic pigments), cadmiums, cobalts, organic reds, oranges and of course whites.
Now, let's say one wants to use Blockx oil paints to create grisaille underpainting using chromatic black (e.g. burnt umber and ultramarine) and flake (lead) white and then lay a glaze over it with transparent mars yellow and the painting will be done according to what George wrote, i.e. applying paint straight from the tube, and paint thinly.
Ultramarine and Flake white are in poppy oil, burnt umber is in linseed oil. Seems to me, that burnt umber is stronger than ultramarine, so more ultramarine will be necessary. Then, as grisaille needs to be bit lighter than a final painting would be in grayscale, relatively large proportion of white will be necessary; of course it can vary depending on particular part of painting, but my point is – this will result in paint layer consisting mostly from poppy oil as a binder. Let's say it'll be left to dry and cure for two weeks, and then the glaze based on Transparent mars yellow will follow; in case of this color, linseed oil i sused as a binder.
Therefore, it will be a paint layer with pure linseed oil as a binder over a paint layer with mostly poppy oil as a binder; is this alright? According to what I know and read so far, I'd say - not really... as oils like poppy and safflower should not be used in lower layers, because they form weaker layer. And yet, so far I haven't read any article or blog post about paint layers cracking in such situations.
I wonder, if it is really a problem, when one uses „weaker" oil like poppy underneath „stronger" oil like linseed. Whether it is only about oil, or also about pigment; lead white is known to make strong and flexible paint layer; is it possible that lead white in poppy oil will still dry into paint layer as strong as some other pigments in linseed oil?
What do you think about it?
