Problems making casein paint
I've been experimenting with making casein paint using borax and casein powder. I've tried the Natural Pigments recipe and the Earth Pigments recipe (they are quite similar except the the Natural Pigments recipe uses a bit less borax and heats to a higher temperature).
The paint/binder produced is translucent with a yellowish color. It dries to a hard, brittle film and it seems to make an excellent paint.
However ... I need the paint not to be soluble in water ... or at least to be very water-resistant, and unfortunately this is not happening with my paint. It is almost as water-soluble as watercolor paint.
The literature says that casein paint is water insoluble when dry ... but mine is not, even after a few days.
Advice would be most welcome!!