This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
The hats should be at first strongly galled by boiling a long time in a decoction of galls with a little logwood so that the dye may penetrate into their substance; after which a proper quantity of vitriol and decoction of logwood, with a little verdigris, are added, and the hats kept in this mixture for a considerable time. They are afterwards put into a fresh liquor of logwood, galls, vitriol, and verdigris, and, when the hats are costly, or of a hair which with difficulty takes the dye, the same process is repeated a third time. For obtaining the most perfect color, the hair or wool is dyed blue before it is formed into hats.
The ordinary bath for dyeing hats, employed by London manufacturers, consists, for 12 dozen, of 144 pounds of logwood; 12 pounds of green sulphate of iron or copperas; 74 pounds verdigris. The logwood having been introduced into the copper and digested for some time, the copperas and verdigris are added in successive quantities, and in the above proportions, along with every successive 2 or 3 dozen of hats suspended upon the dripping machine. Each set of hats, after being exposed to the bath with occasional airings during 40 minutes, is taken off the pegs, and laid out upon the ground to be more completely blackened by the peroxydizement of the iron with the atmospheric oxygen. In 3 or 4 hours the dyeing is completed. When fully dyed, the hats are well washed in running water.
Straw hats or bonnets may be dyed black by boiling them 3 or 4 hours in a strong liquor of logwood, adding a little copperas occasionally. Let the bonnets remain in the liquor all night; then take out to dry in the air. If the black is not satisfactory, dye again after drying. Rub inside and out with a sponge moistened in fine oil; then block.
Red Dye.—Boil ground brazil wood in a lye of potash, and boil your straw hats in it.
Blue Dye.—Take a sufficient quantity of potash lye, 1 pound of litmus or lacmus, ground; make a decoction and then put in the straw, and boil it.
Felt hats are dyed by repeated immersion, drawing and dipping in a hot watery solution of logwood, 38 parts; green vitriol, 3 parts; verdigris, 2 parts; repeat the immersions and drawing with exposure to the air 13 or 14 times, or
until the color suits, each step in the process lasting from 10 to 15 minutes. Aniline colors may be advantageously used instead of the above. For a stiffening, dissolve borax, 10 parts; carbonate of potash, 3 parts, in hot water; then add shellac, 50 parts, and boil until all is dissolved; apply with a sponge or a brush, or by immersing the hat when it is cold, and dip at once in very dilute sulphuric or acetic acid to neutralize the alkali and fix the shellac. Felt hats can be bleached by the use of sulphuric acid gas.