5.3. How to Make Wood-filling

Usually the animal glue is used for the wood-filling material. The glue is crudely made gelatin. The glue has a small amount of impurities and the impurities produces size harder.

However, the glue smells bad and needs devoting time to dissolving in water. Using the powder cooking gelatin instead of glue is possible. The powder cooking gelatin is odorless and dissolving is very easy: just add the powder cooking gelatin in hot water after soak it in a little water in a few minutes.

Dissolve the glue in hot water and add alum; adding chrome alum produces a harder sizing. Do not boil this colloidal solution: the main component of the gelatin is protein and the gelatin loses the property of coagulating at over 80°C (176°F).

The gelatin which coagulated with alum once is not water-soluble. This solution is called "size", and used for sizing and restoration of the old paintings.

Do not make too thick size: if the size is too thick, it does not soak into the plywood. Too thick size would coagulate on the surface of the plywood board and be peeled off by roller when an ink is painted on the printing plate with a roller.

It is possible to use casein instead of the glue. However, it needs ammonia solution for dissolving powdered casein into liquid. It means it smells terrible like the toilet.

The printing plate applied casein is on the market in Japan but the size is still small for the works of professional artists.