Scientific American 1, 4.7.1863
Dyeing Mixed Goods Black. - Cloth made of mixture of cotton and wool or flax and wool has become very common, and in order to obtain black goods of this composition, the practice formerly pursued was to dye the cotton warp first, then the wool of the filling or weft afterwards. It is very difficult to dye fabrics composed of mixed vegetable and animal fibers. They are so different in their nature that different processes are generally required to dye them the same color. Difficulties having been experienced in dyeing mixed cloth black by the old mode of coloring the cotton first, and a superior and more convenient mode has been desired. This is secured by coloring the wool in the piece of cloth first, and the cotton afterwards. The wool is prepared by boiling it first in a mordant of the bichromate of potash, then in a bath of a decoction of logwood, in the usual way now practiced of dyeing black on wool. After the cloth is washed it is steeped for about six hours in a weak decoction of sumac - one pound of sumac being sufficient for ten pounds of cloth. The sumac liquor must be cold or it will tend to make the wool brown in color. After this the piece of cloth is run through some weak lime-water, then through a weak solution of the sulphate of iron, aired and washed. After this it is again run through a weak liquor of logwood, washed, dried and the processes are complete. The acetate of iron is superior to the sulphate of iron for treating the cloth in the second process, and is to be preferred when it can be obtained. Black on cotton soon fades, and becomes a slate color when exposed to sunlight and rain. This is one reason why some mixed woolen and cotton goods soon become faded in appearance. The sulphate of copper is sometimes used for dyeing black on wool, especially for homespun cloth. It is an objectionable substance to use for this purpose, as the light acts upon black thus dyed, and it soon fades into a dirty drab shade. The same process that is pursued to color cotton will also color flax. Fast blacks are dyed on cotton for the cloth of Scotch gingham designed for umbrella covers, by dyeing it first a dark indigo blue, then a black on the top of this with sumac, copperas and logwood. A fast black can also be dyed upon cotton and flax with madder as a substitute for logwood, but these fast blacks are very expensive. It is not generally known that the dyeing of vegetable fibers, such as cotton and flax, involves far more intricate processes, more skill and expense than the coloring of wool and silk. Aniline colors have not yet been applied to dye cotton except for very light shades, they being too expensive for cheap fabrics.
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