Originally Posted by Harold Roth
You are right--it sure is darn hard to find any research or historical info on casein. Have you used casein + oil paints regularly? Or have you noticed how they last? I am real tempted to play with this combo more. Do you think I could still call it "oil paints"? Or would it have to be "mixed media"?
Cannot say I have used it regularly, the samples I made on paper some years ago are currently in storage. When I get back to get that box from their storage location I will see about how they have done. Last check before storing, the layer looked as good as when I painted the sample (a mixture of ultramarine blue and transparent oxide yellow oil paint). The resulting gray paint was in excellent shape and still flexed fine with the paper, though I did not try folding it through the sample (not trying to break my sample yet). The sample was thinly applied, not a heavy impasto at all, which is recommended to avoid for Casein or oil on a flexible surface such as paper.
I would still call it oil paint, as oil painters add all sorts of mediums to their artwork very frequently. Sometimes they add alkyd, wax, resins, varnish, spirits of various types, chalk, egg, or any number of other additives. So long as it looks like oil when finished, it largely doesn’t make too much of a difference. The matte quality of Casein does have a very different look than most oil though. The major thing to remember is that Casein is more brittle and less flexible than oil, so if mixing it in with your oil, do it in the earlier layers and be sure to add less in later layers. Flexible > inflexible.
Nadia_gnar, you are welcome for the link, big thanks go out to Ms McKee for sharing her findings in a nice condensed form for us.
Trond, that was my finding as well. It was when I noticed the oil in the Shiva line of paint that I started researching the compatibility of the mediums.