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MITRA Forum Question Details

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  • Spots on Oil PaintingApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2018-11-28 12:33:33 ... Most recent comment 2018-12-31 16:02:26
    Oil Paint Solvents and Thinners

    ​Anyone know what these spots could be that are showing up on my oil painitng? I normally stain the canvas, but this time I opted to paint right on the white gesso. I did just clean my paint brushes, so worried maybe they werent all the way dry? I am using Geneva Oil paints and I used some Neo Megilp to cover the sky area. I can blend these out but then they show back up the next day. Any advice on how to remedy this is much appreciated! One picture is a close up of the problem area, the other is the whole painting, thought I find these mostly on the left side I have spoted a few in the lighter areas to the right. Screen Shot 2018-11-28 at 12.30.41 PM.png

    Screen Shot 2018-11-28 at 12.30.56 PM.png

Answers and Comments

  • EditDeleteModerator Answer

    ​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?

    Kristin deGhetaldi
    2018-11-28 22:37:34
  • ApproveRejectUn-ApproveUser Comment

    Could it be efflorescence? Geneva paints contain a ton of stand oil.


    2018-12-30 13:16:44
  • EditDeleteModerator Answer

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

    Brian Baade
    2018-12-30 17:46:45
  • EditDeleteModerator Answer

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

    Kristin deGhetaldi
    2018-12-30 17:51:58
  • ApproveRejectUn-ApproveUser Comment

    ​Via the WAAC Newsletter (Volume 20, No. 1):

    "Linseed stand oils contain higher levels of free fatty acids because of thermally induced triglyceride cleavage. Koller and Burmester deduced that a stand oil had been used in the extensively efflorescing areas on a painting by Serge Poliakoff because of the presence of the high amount of free fatty acids and isomerized linoleic acids found in the paint film." 

    (Koller, J., Burmester, A. Cleaning, Retouching and Coatings, Technology and Practice for Easel Paintings and Polychrome Sculpture, Preprints of the Contributions to the Brussels Congress, 3-7 Sept. 1990, Int. Inst. for Con., London, 1990, pp. 138-143.)

    And yeah--I'm wary of Geneva paints because of the clove oil, too. 

    2018-12-31 11:36:47
  • EditDeleteModerator Answer

    ​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 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!

    Kristin deGhetaldi
    2018-12-31 16:02:26
  • ApproveRejectUn-ApproveUser Comment

    ​Just to close the loop on this. Jessica had to replace the canvas:

    Someone else had a similar problem and suggested that it was due to a fault with the manufactorers gesso on the canvas.

    2019-01-05 04:01:42

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