MITRA Forum Question Details

Sorry for the late response. Richeson recommends casein as an underpainting for oils, and instructs that it can be used over acrylic dispersion painting ground (gesso). They caution against applying casein over any ground containing oil, so that would also include alkyd and traditional "oil gesso" formulas. I think the proposed thin underpainting would be a sound approach, avoiding impasto and broad, thick applications. Ampersand recommends a rigid (panel) support for casein, so I would follow that advice and avoid using stretched canvas, even with thin applications.

http://www.richesonart.com/products/paints/richesoncasein/richcaseinfaq.html​

https://ampersandart.com/casein.php

I am afraid that rather than having the benefits of both mediums, mixtures like this generally end up having the deficits of both and lack the virtues of either. Certainly very small amount of oil can be, and are, added to casein emulsions. A representative from Richeson mentioned that they add small amounts of oil to their Shiva Casein paints during our materials session at CAA this February. This is probably only added as a plasticizer and for tube stability. Casein is a very brittle binder and a tiny amount would probably lessen this to a small extent. I would still not recommend painting casein paints on canvas.

There are technical reasons not to add oil in substantial amounts to casein. Casein containing large amounts of oil are known to yellow strongly. Mayer strongly cautions against this. It is certainly true that mixing oil paint with casein paint is not really creating an emulsion unless the two were vigorously mixed and mulled and even then a proper emulsion is probably not created. You would likely create a paint that had swirls of very brittle casein between or surrounding bands of very flexible (at least initially) oil paint. That is a perfect recipe for cracking and paint delamination. Additionally, it is really not technically possible to create a paint that really straddles the emulsion inversion point and allows for alternating between water and organic solvents. These mixtures are physically far more complicated than this. This subject was brought up many times by scientists at the recent tempera conference hosted by the Dorner Institute in Munich.

Coincidentally, the mixtures that you mention actually remind me of the “mixed technique” popularized by Max Doerner where egg tempera/oil/resin emulsions were painted into oil glazes. These were very successful at creating effects that were hard to accomplish by other means but unfortunately resulted in paintings that were prone to cracking and delamination, excessive yellowing, and solvent solubility.