This paint is suitable for absorbent surfaces. It can be oiled or waxed so it can be wiped clean.
Sift Casein into water and soak 12 hours or overnight. Add hot water to Borax, stirring until dissolved. Stir this mixture into the casein and allow it to sit for at least one hour, possibly longer, until the Casein particles have all absorbed. You should have a yellow, translucent mixture. Heat this mixture to 140 ºF using a double boiler then allow it to cool. It will become syrup-like and can then be mixed with pigments.
Pre-wet your pigments with water and add the casein syrup to the pigments until you have the right proportions. This will depend on the pigment used and color desired. Be sure to do the recommended testing to be sure the casein/pigment ratio is correct. If it powders, add more binder. If it cracks, add more pigment. Thin this paint with water for use.