This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
The solution of stannous chloride necessary for the preparation of gold purple is produced by dissolving pure tin in pure hydrochloric acid (free from iron), in such a manner that some of the tin remains undissolved, and evaporating the solution, into which a piece of tin is laid, to crystallization.
Recipe for Pale Purple.—Dissolve 2 parts by weight of tin in boiling aqua regia, evaporate the solution at a moderate heat until it becomes solid, dissolve in distilled water and add 2 parts by weight of a solution of stannous chloride (specific gravity 1.7) dilute with 9,856 parts by weight of water, stir into the liquid a solution of gold chloride prepared from 0.5 parts by weight of gold and containing no excess of acid (the latter being brought about by evaporating the solution of gold chloride to dryness and heating for some time to about 320° P.). This liquid is dimmed by the admixture of 50 parts by weight of liquid ammonia which eliminates the purple. The latter is quickly filtered off, washed out and while still moist rubbed up with the glass paste. This consists of enamel of lead 20 parts by weight; quartzose sand, 1 part by weight; red lead, 2 parts by weight; and calcined borax, 1 part by weight, with silver carbonate, 3 parts by weight.
Recipe for Dark Gold Purple.— Gold solution of 0.5 parts by weight of gold, solution of stannous chloride (specific gravity 1.7) 7.5 parts by weight; thin with 9,856 parts by weight of water, separate the purple by a few drops of sulphuric acid, wash out the purple and mix same with enamel of lead 10 parts by weight and silver carbonate, 0.5 parts by weight.
Recipe for Pink Purple.—Gold solution of 1 part by weight of gold; solution of 50 parts by weight of alum in 19,712 parts by weight of water; add 1.5 parts by weight of stannous chloride solution (specific gravity 1.7) and enough ammonia until no more precipitate is formed; mix the washed out precipitate, while still moist, with 70 parts by weight of enamel of lead and 2.5 parts by weight of silver carbonate. According to the composition of the purple various reds are obtained in fusing it on; the latter may still be brightened up by a suitable increase of the flux.
Take verdigris, 50 parts by weight and very strong vinegar, 100 parts by weight. Dissolve the verdigris in the vinegar, rub the pieces with it well, heat them and dip them in liquid ammonia diluted with water. Repeat the operation if the desired shade does not appear the first time. Rinse with clean water and dry.
Gilt objects are improved by boiling in the following solution: Saltpeter, 2 parts by weight; cooking salt, 1 part by weight; alum, 1 part by weight; water, 24 parts by weight; hydrochloric acid, 1 part by weight (1.12 specific gravity). In order to impart a rich appearance to gilt articles, the following paste is applied: Alum, 3 parts by weight; saltpeter, 2 parts by weight; zinc vitriol, 1 part by weight; cooking salt, 1 part by weight; made into a paste with water. Next, heat until black, on a hot iron plate, wash with water, scratch with vinegar and dry after washing.