Black upon Cotton by Dyeing.

Scientific American 8, 21.8.1869

The old fast black upon cotton was obtained by giving a blue ground with indigo, then galling and working in sulphate of iron, sometimes with addition of logwood; alder bark, and other similar substances were also employed; and the goods usually finished in an emulsion of oil, to take off the harshness which iron mordants so generally communicate. Later on, what was called the Manchester black, was obtained by first steeping in galls or sumac, then working in the copperas vat, and afterward in logwood containing some verdigris, and repeating these opetations until the desired shade was obtained. Galls are now scarcely ever used; sumac, which is cheaper, being employed in substitution; and the processes, though almost infinite in details, consist essentially of steeping in sumac, then working in an iron bath, and afterward raising in logwood.

One method said to give good results, consists in steeping in sumac for twelve hours, then working through lime water and exposing to the air until the light green color at first produced passes to a dull heavy shade; the goods are then passed through a solution of green copperas, and exposed to the air until they appeared black while in the wet state; if dried they would be found to be only gray or slate color. To fill up the color the goods are passed into the logwood bath (some authorities say it is advidible to pass them through lime water first) for a sufficient time; lifted, some copperas added and the goods raised in it; for light goods this suffives to produce a black, heavier goods require a repetition of the processes. A rapid continuous method of dyeing lack on light goods is practiced in Lancashire; the goods are passed through a decoction of catechu, then immediately into a solution of bichromate of potash, next into decoction of logwood, then into green copperas, and lastly through a decoction of some red wood, as camwood or Brazil wood. The order of these liquids may be changed within certain limits.

A simpler method of dyeing by means of bichromates is also given, which consists in steeping the goods in logwood, exposing them to the air and drying, then passing them into bichromate of potash neutralized by crystals of soda, by which the logwood is "struck" of an intense black, and fixed. Velveteens are dyed black by reiterated passages in logwood and green copperas until a dark brown is produced, then passed in sumac and sulphate of copper, with sometimes addition of peachwood or Brazil wood. Fustic is an ingredient in all dyes where a brownish or jet black is desired.

Black is one of the most difficult colors to dye, and no one but a practical man understands the difficulties of obtaining regular and good results, wspecially when first-class colors are aimed at. It is useless to give weights and quantities when these are really only inferior elements of success; a slight change in the quality of the sumac, some thing different in the "ageing" or "mastering" of the logwood, some slight modification in the temperature and pressure of the "stills" in which the liquors are made, and other causes not more conspicuous, have frequently in my experience put works almost to a stand still. And when I have been called in for advice, it has been ecident that chemistry could only give conjectures as to what was wrong.

These failures in producing satisfactory colors would not be apparant to an unpractised eye; the defects would only consist in those hues and reflections of shade being wanting which were most esteemed and usually produced. Though it is exceedingly difficult in most cases to trace the actual cause of inferior results, there have been in my practise very evident occasiuns in which a most trivial and apparently unimportant cause has produced very embarrassing effects; the closest attention on the part of a foreman or manager is most essential in order that these things may be avoided, or if they occur that their cause may be discovered. - Dictionary of Dyeing and Calico Printing.

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