DYEING DIRECTIONS

For cotton and linen, measure out the color and dissolve it in hot water to which has been added twice its amount of sodium sulphide (crystals) and a quarter or third the amount of soda ash. (In all these formulæ washing soda may be used in place of soda ash—only in quantities almost twice as large.) It is advisable, though not absolutely necessary, to add also to the dye-bath one or two tablespoonfuls of Turkey red oil—a kind of liquid soap made by treating castor oil first with sulphuric acid and then with soda. This prevents the formation of a dark scum on the surface of the dye-liquor, which is likely to cause streaks in the finished goods, hard to wash out.

Into the dye-liquor immerse the well-wetted goods, and heat them, turning them constantly, and keeping them as far as possible away from the air and under the level of the liquid. Just before the boiling point is reached take out the goods, and add salt in the proportion of, say, two spoonfuls of salt for every teaspoonful of dyestuff used. Stir till the salt is all dissolved, put the goods back, and continue to turn them as before, keeping the goods down under the liquor and not allowing it to boil.

After dyeing just below the boiling point for fifteen minutes, remove the heat, take out the goods, and—as quickly as possible—run them carefully backward and forward through the wringer (changing the folds of the goods each time) until the excess of dye liquor is entirely squeezed out. Then shake them out, hang them up for fifteen or twenty minutes in the air to oxidize and “set,” and after this wash them thoroughly in a bath of boiling soapsuds until all the loose color has been removed. Finally, rinse them free from soap, and hang up to dry.

When light shades are desired, or when the goods are tender, the dyeing can be done at lukewarm temperature, and without the addition of salt, with no detriment to the fastness of the color. In this case, however, much of the dyestuff will be wasted in the unexhausted dye-liquor.

List of Selected Dyestuffs.—

Badische—Kyrogene Brown, R R O
Kyrogene Yellow, G G, extra
Kyrogene Direct Blue, 3 B, extra
Kyrogene Black, T G O
Cassella— Immedial Bordeaux, G
Immedial Yellow Olive, 5 G
Immedial Direct Blue, B
Elberfeld—Katigen Yellow, G F, extra
Katigen Indigo, C L G, extra
Katigen Deep Black, B
Kalle—Thio Indigo Red, B
Thion Yellow, 3 G, extra
Thion Blue, B, conc.
Thion Black, G, conc.
Metz—Thiogene Brown, G R
Thiogene Gold Yellow, A
Thiogene Green, G
Thiogene Cyanine, G
Thiogene Black, M A, extra strong

These Sulphur colors are particularly strong in various shades of black, blue, and brown. Some of the yellow shades, also, are very fast and good. The class is deficient, however, in reds—the only one so far discovered being Thio Indigo Red B (Kalle), which really belongs to the Indigo or Vat colors, described in the next chapter, and which does not give very powerful shades when used as a Sulphur color. As a rule, these dyes produce shades that are softer, deeper, and much less brilliant than those of the Direct Cotton or Salt colors. Being usually mixed, and not simple primary, colors, they are not very easy to dye to shade, especially as the color of the freshly dyed goods changes considerably while it is being oxidized. On the other hand, they give, without mixing, extremely pleasant tones, and are all very fast to washing and, at any rate as regards the selected colors, are fast to light.

When exposed to strong direct sunlight some even of the best of them are liable to change their shade somewhat; but even then they will be found to fade to nice, soft shades not out of harmony with the original. When very great fastness to light is necessary, it may be worth while to after-treat them as described in Chapter III, by keeping the dyed goods for twenty or thirty minutes in a hot bath (not boiling) containing small amounts of copper sulphate, bichromate of potash, and acetic acid.

Chapter VI
THE INDIGO OR VAT COLORS

History.—Most of the colors of this group have been discovered and put on the market within the last two years. Thus they form the most recent as well as, in many respects, the most interesting and, perhaps, the most important class of modern dyestuffs. On the other hand, to this same group belong not only indigo itself, which has been known and valued in the East from the earliest ages, but also that most famous of all the ancient dyestuffs, Tyrian Purple.

Indigo itself does not exist as such in nature; but it is easily formed by oxidation, or the exposure to air, of a substance—Indican—which occurs as such, or can be produced by a simple process of fermentation, in the juices of many widely distributed plants. Accordingly, even quite barbarous races in different parts of the world noticed the deep permanent blue stains formed on their bodies and clothing when they crushed, accidentally or on purpose, the leaves and stems of the variousIndigoferæ. Gradually they learned to extract the color in a solid and permanent form so that they could dye with it, instead of using the juice of the fresh plant itself—and then they took to cultivating the plants.

These plants—Indigofera Anil,I. tinctoria, and others originally found wild have been, up to the last four or five years, extensively cultivated in many tropical countries, notably in India (some of the best qualities came from the province of Bengal, and hence the common name for the natural dyestuff—Bengal Indigo), Japan, China, Java, South and Central America, and Africa. From these plants the indigo of commerce, in the form of dark blue granular lumps with a characteristic coppery lustre, was prepared by a comparatively simple process of fermentation, extraction, and oxidation.

Indigo may also be obtained, although in small quantities only, and in an impure condition, from other plants. Notably among these isIsatis tinctoria, or woad, which in early days was extensively cultivated in England and the Continent, and which, even now, is used in small quantities in some processes of indigo dyeing.

Artificial Indigo.—The exact composition of indigo was first determined some sixty years ago, and from that time on some of the greatest chemists of the world have been attempting to prepare it, artificially, from some comparatively inexpensive source, obtained from coal tar or elsewhere. As early as 1875 the problem was solved, at least from a scientific standpoint, but the process proved too expensive for commercial purposes. During the last five years, however, at least two of the great German firms have discovered methods for making, in any desired quantities and at very reasonable expense, absolutely pure indigo from some of the important coal-tar derivatives. And since that time the cultivation of the indigo plant has proved so unprofitable that it has been almost entirely abandoned, and the land formerly used for this crop is being turned over to other and, at present, more useful purposes.

This synthesis—i.e., chemical formation—of indigo from coal-tar products has been justly regarded as one of the great triumphs of modern science. Right here let me impress upon my readers this fact: the real dyestuff, indigo, is absolutely the same material, whether it comes mixed with a great mass of impurities, as in the woad; or whether it contains from 5 to 25 per cent. of foreign matter of little or no value, as in the Bengal or natural indigo; or whether we get it from Metz or the Badische Company, chemically pure, either in the dry state or, thinned with water, in the form of a 20 per cent. paste. It is positively the same dye; and being absolutely without contamination of any kind, the artificial or synthetic dyestuff presents advantages in the matter of purity of shade, ease and surety of manipulation, and permanence of the color produced, which could never be obtained before its introduction.

Application of Indigo.—The principles of indigo dyeing are the same now as with the Egyptians, the only difference being in the means used to bring about the chemical changes involved. Indigo itself is a blue solid, insoluble in water, acids, and alkalies, and practically unaffected by sunlight. If, however, the element hydrogen be added to it, or, as the chemist would say, if it is “reduced” by the action of any one of numerous deoxidizing or reducing agents, the indigo blue is changed to a new substance, indigo white, which is almost colorless, and which dissolves, in the presence of alkalies, to a bright yellow liquid. If cotton, wool, paper, wood, or indeed almost any solid materials (noticeably the fingers and nails, as some of my readers may find out), are immersed in the solution, they will absorb some of this indigo white, and then, on exposure to the air, the white indigo will rapidly take up oxygen, and become converted into the insoluble blue coloring matter.

Fermentation Method.—Until recently the methods used for reducing the indigo—i.e., changing the solid blue into the soluble white—were just about the same as those used by the ancients, and were based upon some kind of fermentation, usually alcoholic. It was found out at a very early date that if indigo, ground up with water to a paste and rendered alkaline by the addition of wood ashes, lime, or other simple alkali, were mixed with grape juice or any other sugary liquid, and then kept warm and allowed to ferment, the resulting fluid would contain the dyestuff dissolved in a form suitable for dyeing. The vessel in which this process was conducted was known as a vat, and the process of indigo dyeing is still called “Vat Dyeing.”

Disadvantages.—At the very best this method is slow, uncertain, and difficult to manage, especially on a small scale. In wool dyeing, to this day, a few vats are still to be found where syrup, ground madder root or, in some instances, woad, wheat bran, and other materials which ferment readily in the presence of alkali, are stirred up with warm water and soda, and then allowed to stand. In two or three days they are in active fermentation, and the indigo, in the form of paste, is added and well stirred in. After much further delay, if all goes well, the indigo is finally “reduced,” and, if the amount of alkali, the temperature, the concentration of the vat, and various other factors are carefully attended to, the bath can be used for several days, or even weeks, without being made over again; fresh indigo and other ingredients being added, from time to time, as needed. Cotton, linen, wool, and even silk can be dipped in this bath, which should be light greenish yellow in color, with a blue or bluish-green scum or coating, where the indigo is oxidized on the surface. Goods immersed in this bath turn yellow, and then, when taken out, wrung free from loose liquor, and exposed to the air, the yellow color quickly changes to a permanent blue.

A serious drawback to all these various fermentation vats is that a good deal of the dyestuff is always spoilt—i.e., decomposed into colorless compounds which can never be regenerated or made useful. Indeed, the loss from this cause frequently amounts to 20% or 25% of all the dye used, and occasionally, especially in hot weather, and on a small scale, to far more.

But, apart from the actual loss in valuable dyestuff, there is a much more serious drawback to this method of indigo dyeing, namely, the waste of time and energy involved. There is always a considerable delay in getting a fermentation vat fairly started, even where all the conditions are favorable; and when it is running smoothly, the reducing process is a very slow one. Furthermore, the indigo, not being dissolved in the liquid but only suspended in it, has a constant tendency to sink to the bottom in the form of a blue mud, and thus escape the chemical action of the fermentation gases entirely.

A short time ago a teacher of handicraft dyeing was expatiating, in my presence, upon the impropriety of using any of the new chemical processes for dyeing, and insisted that the only way to dye indigo was to set up a vat, and feed it, and work with it as our ancestors used to. It was suggested to her that it would be at least two or three days before cloth could be dyed in such a vat. “Eight or ten days at the earliest,” was the reply. And when it was hinted that the vat would have to be frequently stirred during all that time, she proudly answered, “Stirred regularly and thoroughly every single half-hour, night and day, during the whole period.”

“H—m,” remarked a bystander, “that’s a little worse than sitting up with a baby sick of the croup.”

Somehow the great advantage of this particular process over the modern ones, by which a proper bath can be prepared in perhaps five minutes, failed to impress itself on some of her listeners.

Modern Chemical Vats.—As soon as it was understood just what chemical action was going on in the vats, and the object of it, chemists began to find out methods for reducing the indigo without the necessity of a long, tedious, and even nasty fermentation process. They first introduced the “copperas-lime” vat, where the reduction was done by the use of ferrous sulphate (green vitriol or copperas), and slaked lime was the alkali used to keep the indigo white dissolved.

Later they introduced zinc dust, a very powerful reducing agent, in place of the copperas, avoiding in this way the large amount of precipitated iron oxide which always forms in the copperas vat, and leads to the loss of dye, and muddiness and dulness of color, necessitating a special clearing bath of dilute mineral acid.

At present the most satisfactory method is to use the chemical known assodium hydrosulphite, as a reducing agent, in a bath made strongly alkaline with caustic soda. Hydrosulphite is not expensive; it acts very rapidly, leaving no sediment; it causes no loss or waste of the indigo; and it does its work perfectly. Hence, with its introduction, the dyeing of indigo has become extremely simple.

To still further shorten and simplify the process, the large manufacturers not only furnish indigo already ground up to a fine paste with water, but also supply it already reduced by hydrosulphite or some other reducing agent, so that it is almost ready to dye with as it is, and will dissolve almost instantaneously in an alkaline bath with the addition of just a little more reducing agent. Such products are the Indigo Vat III (Metz), and the Indigo Solution 20% (Badische). By using either of these, the preparation of a vat large enough to dye 3 or 3½ pounds of cotton is the task of but a few moments. These special preparations, however, are more expensive than the regular 20% pastes, and the hydrosulphite vat is so easy to prepare that the saving of time is hardly worth the extra cost.