Casein is the protein component of milk, and it makes great paint. Casein paint lasts indefinitely, is excellent on many surfaces, isn’t prone to fungal growth, and leftover paint can be safely composted. Casein paint is prepared from the curds of nonfat milk (fats inhibit drying time). These are also known as quark, and are available in gourmet grocery stores, but they’re easy to make yourself. Or you can purchase concentrated casein powder from a natural paint supplier. (To use casein powder instead of quark, just follow the label’s instructions.)
Casein paint must be mixed to specific proportions to prevent cracking, peeling and dusting off. It’s important to allow each coat to dry completely, because the paint will become more and more opaque as it dries. Avoid the temptation to apply extra-thick coats!
In order to become an adhesive binder, casein must be combined with an alkali such as lime. (You can use borax instead, but lime-casein paint is much more water resistant.)
Yields about 1 quart
1 gallon nonfat milk
2 1/2 ounces “Type S” lime (dry powder available at hardware stores)
2 1/2 cups water
Natural earth pigment (more or less depending on desired color)
6 cups filler (usually whiting)
After mixing your paint, test it on a small area of your surface and let it dry completely. If it doesn’t spread easily, add some water. If it dusts, add more binder. If it’s too thin, add more filler. If the color isn’t rich enough, add more crushed pigment.
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