The blue dyes derived from coal tar are very numerous, direct, basic, acid and mordant blues being known. The direct and basic dyes are very little used, but the acid and mordant dyes are extensively employed, as is indicated in the following recipes.
Dyeing with Direct Dyes. Pale Blue.--Prepare a dye-bath with 1/2 lb. Sulphon Cyanine and 10 lb. Glauber's salt. Enter the goods, and work at the boil for one hour, then lift, wash and dry.
Black Blue.--Prepare a dye-bath with 3 lb. Sulphon Cyanine, 5 lb. Glauber's salt, and 5 lb. acetate of ammonia; work at the boil for one hour. Sulphon cyanine works well with other dye-stuffs, and gives shades which are fast to milling.
Dyeing with Acid Dyes. Bright Blue.--Prepare a bath with 2 lb. borax and 1 lb. Alkali Blue B. Enter the wool at about 170° F., then heat to the boil, and work for half an hour; then lift, rinse lightly, and pass into a weak sour bath, with sulphuric acid to raise to the colour.
Soda may be used in place of borax, but the latter salt maintains the softness of the wool fibre better.
By using various brands of Alkali Blue (3 R to 7 B), various shades of blue from a reddish with the 3 R to a pure blue with the 6 B and 7 B brands may be dyed. The Alkali Blues are fairly fast to light.
Dark Blue.--Prepare a dye-bath with 2 lb. Serge Blue, 10 lb. Glauber's salt, and 2 lb. sulphuric acid, working at the boil for one hour. This is a very common way of dyeing blues on serges, cashmeres and worsted goods. In place of serge blue, what are known as Blackley blues, or Dewsbury blues, may be employed. These have a similar composition, but vary a little in the tint of blue they give.
Navy Blue.--Prepare a dye-bath with 2 lb. Induline A, 10 lb. Glauber's salt, and 2 lb. sulphuric acid, working at the boil for one hour.
The Indulines are very useful colouring matters for dyeing navy or dark blues on wool. They have the defect of being liable to give uneven shades. This may be remedied by omitting the acid when first making up the bath, entering the wool, working for half an hour to thoroughly impregnate the material with the dye-liquor, then adding the acid, and continuing the working for another half-hour. Or the wool may be treated to a weak chlorine bath before it is dyed, by first passing it through a weak hydrochloric acid bath and then through a bath of bleaching powder. By using acetic acid in place of sulphuric acid more even shades are obtained.
Blue.--Prepare a dye-bath with 1 lb. Acid Blue 1 V, 9 oz. Acid Violet 1 V, 10 lb. Glauber's salt and 2 lb. sulphuric acid, working at the boil for one hour.