Nearly thirty years ago one of the French color houses put on the market a new dyestuff which it named “Cachou de Laval”; Cachou being the same as catechu or “cutch,” the natural brown dyestuff long known and used in the East, and Laval being the name of the town in France where one of its discoverers was born.
This dyestuff was made by heating sawdust, bran, turf, leaves, or other vegetable substances with the strongly reducing alkaline salt,sodium sulphide, in the absence of air. The product, dissolved in water, makes a dark green solution which, after standing in the air a short time, turns brown and deposits a fine brownish powder. Cotton or linen, heated in a fresh solution of this dyestuff, is colored green, but, when wrung out and exposed to air, the green color, which easily washes out, changes into a very permanent, though dull and uninteresting, shade of greyish brown.
This Cachou de Laval was not a success, commercially, because of its poor color. It existed, however, as a chemical curiosity for some twelve or fourteen years; then suddenly, within a few months or even weeks of one another, all the great color houses put out a whole series of colors—chiefly browns, blues, yellows, and blacks—all formed, like this old “Cachou de Laval,” by the action of sodium sulphide or, which amounts to the same thing, of sulphur and caustic alkali, upon organic material, and all capable of dyeing cotton and linen, in one bath, colors extremely fast to washing and generally quite fast to light, after they have been “set” by exposure to the air.
While in general these are known and identified as the Sulphur colors, the different manufacturers have given special class names to their own series thus:
Immedial (Cassella), Katigene (Elberfeld), Kyrogene (Badische), Pyrogene (Klipstein), Thiogene (Metz), Thion (Kalle).
These colors are used almost exclusively for dyeing cotton and linen, when shades fast to washing are required, without first putting them through a mordanting process. The dyeing is done in one bath, with little more difficulty than in the case of the Salt colors described in the last chapter; and, while not faster to light than the best of that class, they are not nearly so liable to bleed.
On wool they are rarely, if ever, used. Wool is almost always dyed with the acid colors in an acid bath; and nowadays the range of these colors is so great and the best of them are so very satisfactory, that there is hardly ever a necessity for using colors of another class.
Neither are these Sulphur colors often used on silk, although methods have been devised for employing them in special cases. All the animal fibres, however, and silk especially, are very easily “tendered,” and indeed destroyed, by heating in an alkaline solution. And so it is very easy to spoil a skein or piece of silk by dyeing it, in the usual manner, with these dyes, dissolved as they must be in the strongly alkaline sodium sulphide.
The presence in the bath of glucose (corn syrup, molasses, etc.), or of glue or gelatine, helps greatly to protect these fibres from the action of the chemicals. But even when dyed with great care, using glucose, and dyeing the goods for but a short time in a bath strong in color but weak in alkali, the results are not very satisfactory, so far as shade and lustre are concerned. They have the advantage, however, of being extremely fast to washing, more so, even, than the Salt colors. In general, however, silk should be dyed with the Acid colors for ordinary work, and with the Salt colors when fastness to washing is required. The Sulphur colors should be reserved for cotton and linen.
On mercerized cotton and artificial silk these dyestuffs take easily and well, when dyed in cold or lukewarm baths. The lustre, however, of the finished goods is apt to be less than when Salt colors or Basic colors are used.