Casein paints are coatings for walls and ceilings which contain pure natural milk protein (Casein) as a binding agent. Even since the times of ancient Egypt paints made of milk and pigments were produced and used. Similar paints have been mentioned in old Hebrew documents. Mural paintings in the Sistine Chapel (Secco technique) have been made durable using similar traditional paint.
Later on curd cheese has been used instead of milk, it contains three times more casein (about 12 %). Due to the usage of milk and curd cheese these colours always had to be applied when they were still fresh. They could only be kept a few hours to a few days. Modern casein paints are produced in powder form and contain dried casein. This extends the shelf life to a couple of years. Preservatives became unnecessary, thus reducing transport weight, packaging waste and keeping transportation costs to a minimum.
A recent trend is the usage of casein, based on vegetable protein binder. Vegetable casein derives from protein producing plants like peas, lupines, beans or other leguminous plants. Milk casein is obtained by treating fresh milk with acid or rennet flocculating the protein, so that it can be filtered, dried and pulverised. The protein actually keeps its food quality. Casein alone cannot be used as a binder, it lacks sufficient adhesive force. It will not change into an adhesive before alkalis have been added, which break the protein down. Suitable agents are potash, soda, bicarbonate (baking powder), salts of hartshorn, borax or lime hydrate.
In contrast to most other colour binders the appearance of pigments and filling materials are not altered by casein; hence pigments will shine in their unique typical brilliance. Ecologically, Casein paint is absolutely harmless throughout the whole product cycle (production, use and disposal). Paint residue can even be composted.