Recipe: Casein: Lime-Casein according to Wehlte

Step 1: The fresh curd (5 parts by volume) (also called cottage cheese or pot cheese) is first squeezed in a cloth to remove the excess whey (water and soluble proteins).

Step 2: The resulting crumbly mass is put into a mortar with the slaked lime (5. part by volume). In practice the quantities are never actually weighed, for the proportion need not be exact, unlike with neutral lime-casein. The lime should have a buttery consistency as it comes from the lime pit in which it had been stored.

Step 3: Curd and lime are ground together thoroughly with a pestle. To make certain that the mixtures will not go lumpy, the curd can be ground beforehand.

Step 4: Within the short span of one minute, the hydrolyzation process will be complete. The result is a viscous liquid. It the consistency is slack, the curd contained too much water. Instead of a mortar, one may use a small porcelain, plastic, or enamel dish and a bulbous, wooden stirrer: curd and lime can even be mixed on a color-grinding slab or an ordinary glass plate by carefully working them through with a spatula. The latter method has the disadvantage that casein glue tends to run off the flat plate at the moment of hydrolyzation.

Step 5: Another phenomenon should be mentioned here that can prove irksome with casein. Thick, concentrated casein glue starts to gel, sometimes in as little as one hour after preparation. This makes it useless, since it cannot be liquefied again, neither by warming nor by renewed grinding with a small amount of water. This unpleasant characteristic can be obviated by grinding the colors at once and diluting the remaining medium with water.

Step 6: Diluted casein and casein-pigment mixtures do not gel. All casein paints and even some casein tempera colors are, however, subject to another phenomenon: certain pigments are highly thixotropic. Thixotropy is a curious occurrence found in colloids. It turns normally bound paint in tins into a thick jelly overnight. Even small additions of water would turn this paint into a thin liquid without body.

Step 7: If, on the other hand, thixotropic paint is simply stirred without adding water, it immediately regains it original consistency. Sometimes it is enough to tap the side of the tin, or to knock it on the table a few times, to counteract thixotropy.