Casein can be used to give sculptures an extremely attractive finish. The casein is deposited by steeping the finished sculpture or cast in skimmed milk.
Only skimmed milk can be used for the process.
The sculpture must be steeped in the skimmed milk for some time so that the casein deposits on the surface of the cast.
To avoid using a large quantity of skimmed milk it is good idea to put the object first in a plastic bag, and then fill the bag with milk. After an hour or so the cast is removed and allowed to dry completely. Finishing works with casein is a traditional method although little used today the final polish can be achieved by rubbing French chalk into the surface to give a higher lustre. Casein finished plaster, it has been said, resembles bone. It is well worth trying this finish on some of your work. In this case the Skimmed milk has been applied by brush to buff/white fired terracotta clay.
Casein is the main protein in milk. When removed from milk as a curd, it is widely used in manufacturing as well as in food products such as cheese. Skimmed milk curdled with hydrochloric or sulphuric acid produces “acid" casein than becomes a colloid with excellent binding properties when it is dissolved in water containing an alkali and then dried. Mixed with lime or formaldehyde, it is used to make water-resistant glues, binders in paints, and tough, clear protective coatings for leathers, textiles, lithographic stones, and paper.
Rennet-curded casein, treated with formaldehyde, forms a plastic that is primarily used to make buttons and imitation gemstones