This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
This is done by varnishing them with a solution of shellac, after the following manner: Make a solution of shellac, 1,000 parts; alcohol, 90 per cent to 95 per cent, 1,000 parts; boric acid, 50 parts; castor oil, 50 parts. The shellac is first dissolved in the alcohol and the acid and oil added afterwards. For the first coating use 1 part of the solution cut with from 1 to 2 parts of alcohol, according to the porosity of the wood—the more porous the less necessity for cutting. When the first coat is absorbed and dried in, repeat the application, if the wood is very porous, with the diluted shellac, but if of hard, dense wood, the final coating may be now put on, using the solution without addition of alcohol. If desired, the solution may be colored with any of the alcohol soluble aniline colors. The shel lac solution, by the way, may be applied to the outside of chests, etc., and finished off after the fashion of "French polish."
When used this way, a prior application of 2 coats of linseed oil is advisable.