MITRA Forum Question Details

​Honestly we are also at a bit of a loss here. PERHAPS this has to do with a priming layers that is absorbing your paints unevenly? Can you tell us more about the type of pre-primed canvas you are using? Or is this an acrylic dispersion ground you have applied yourself?

I see no reason to believe that stand oil is more likely to cause fatty acid exudations more than other unprocessed drying oils.

​Regarding Geneva paints and their composition....might be worth reading an earlier thread which you can find here.

​Yes this is a rather well known article.....unfortunately some of the early conclusions on many things to do with the analysis of binding media are now being revisited (characterization of drying oils being one such topic). So I would not be surprised if a) the authors of the particular study cited in paper retracted some of these conclusions and if b) another lab were test the same painting I am almost certain that a different conclusion would be reached. 
But the idea that stand oil may possess MORE free, mobile fatty acids vs. cold-pressed linseed is an interesting one....as far as more up-to-date info regarding the precise mechanisms involved with stand oil I found this article to be fairly thorough. However, we still lack the inability to successfully quantify many of these organic markers....of note is the fact that there is no mention of the PIGMENT(S) involved in this study in the WAAC article so I went straight to the source. Of equal interest in terms of blanching for this particular painting is that the pattern was also directly related to presence of red lake, which was either present in lower layers in the underlaying sketch or in visible paint layers. So that throws another monkey wrench into this study (pigments are the true "headache" for those trying to characterize binding media). What would be lovely to have is a nice study that characterizes and quantifies free fatty acids across a range of different drying oils (pigmented and unpigmented) using a number of different techniques....but I am still waiting for that dissertation to show up in my inbox from someone!