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artasart
10-25-2012, 05:28 PM
Hi all,
I am doing some projects (painting on wood) using emulsions where accelerating the yellowing of linseed oil due to the presence of casein would be beneficial. Can anyone tell me why casein yellows linseed oil? I know that yellowing is usually something to be avoided but in my case, if I could understand a bit better what causes it, my project will be rendered more beautiful by causing more of it!
Thanks for your comments. I'll also post this question to the oil painting experts.
Cheers,
Art

Mayberry
10-25-2012, 10:01 PM
This article might be of interest: http://www.sydneywoodturners.com.au/site/articles/finishing/oils.html

It sounds like it has to do with ammonia in the casein. I don't know if it makes a difference if the casein is made with borax instead.

AmyH
10-25-2012, 10:37 PM
I have never heard of such a thing. Where did you hear that casein yellows linseed oil?

dbclemons
10-30-2012, 10:38 AM
Casein may yellow, depending on how it's made, and linseed may yellow on its own, but the two mixed together will not affect each other.

I've been making my own casein paints and mediums for a long time and have not had any yellowing problems. I typically make my casein with borax, but ammonia or other alkalies should not cause any yellowing. Some casein can be made with formaldehyde or other additives that can cause color changes over time.