Processing
Step 1: 40 g casein powder (#63200), let soak for approx. 12 hours in 125 ml cold water; 16 g crystalline borax (#64000) dissolved in 125 ml hot water. The casein is usually prepared in a large porcelain mortar with a pestle, but any enamelled or plastic bowl will do.
Step 2: While the casein is soaking, the bowl is kept covered with a thick, wet cloth folded several times, which prevents the formation of a dry top layer. No unsoaked granules should remain on the edge of the bowl. It is best to leave it overnight to make sure that the casein absorbs as much water as possible.
Step 3: The hot borax solution is stirred into the granular, pulpy casein and stirred again after a few minutes. It is then left standing.
Step 4: Within 1 - 2 hours one may observe that the viscous, yellowish, translucent mass no longer contains recognizable casein granules, a sign that the hydrolyzation is complete. Nevertheless, it is sometimes left standing up to a full day in order to make the casein medium even more viscous.
Step 5: If casein medium is to be kept for several days or weeks, it must be preserved with a desinfectant. It is advisable to prepare only small amounts of casein and not keep it for long periods.
Step 6: As an additive for size paint it is recommended to dilute the prepared medium with water to a total volume of 1 litre, thus obtaining a concentration of 4% casein in the size paint. 1 litre of casein paint is sufficient to paint about 10 m2 of a smooth and non-absorptive ground.
Note
Borax casein lasts longer when it is hygienically prepared, i.e. using boiled water and clean containers. Borax casein can then be stored for half a year, sometimes even longer, without adding preservation agents.
We assume no liability for the processing instructions described above. In any case, we recommend the production and evaluation of sample surfaces.
