Dyes and dyeing

by Charles Ernest Pellew

DYEING AND STAINING OF LEATHER.

General.—It has been mentioned, in previous chapters, that animal fibres of all sorts, such as wool, silk, feathers, etc., seem to possess at the same time both acid and basic properties, and therefore they combine readily with dyestuffs belonging to the Basic and also to the Acid class. This at once distinguishes animal fibres from vegetable fibres such as cotton, linen, and paper, which, being practically neutral in composition, will not combine with either Basic or Acid dyestuffs without the assistance of mordants.

This same rule applies to leather, and we are therefore able to dye leather successfully with either Acid or Basic dyestuffs, using a dye-liquor made acid with, preferably, a volatile organic acid such as acetic or formic acid.

Acids.—For Basic colors acetic acid is generally used, as being cheaper than the other, and quite as good for dissolving the dyes for the dye-bath. For Acid colors it is generally best to use formic acid, for acetic acid in many cases fails to liberate the color-acids from the dyes, and then the colors fail to “bite.”

Professional leather dyers, for the sake of economy, often use a little sulphuric acid in the dye-bath, a practice which is one of the chief causes of the short life of modern leathers.

With other animal fibres, such as wool and silk, the Acid colors take quite as readily as the Basic; but with leather, there is some little difference, according to the way in which the leather has been prepared.

For our purposes it is hardly worth while to discuss the dyeing of chrome leather or of chamois leather. The leather almost universally employed for hand work has been bark tanned, excepting where very white goods are used, of rather light quality. These are generally tawed with alum, and for this reason have a greater affinity for the Acid colors than when the fibres have already been fully charged with tannic acid, which at the same time, it will be remembered, acts as an excellent mordant for the Basic colors.

Dyestuffs.—Accordingly, while Acid colors may be used, they do not act nearly so readily as the Basic colors. For this reason, except for special shades such as a clear sky-blue or a pure scarlet, which can hardly be obtained excepting by the use of Acid dyes, or where special fastness to sunlight is required, the best Basic colors, such as Methylene Blue, Methylene Heliotrope, Thioflavine T (for yellow) and Safranine (for red) are usually employed. For black, it is well to use one of the many Leather blacks, made by mixing together powerful Basic dyes. For brown, the standard leather color, used in enormous quantities for gloves and the like, is the well-known Bismarck Brown, or for more orange shades, the closely related dyestuff, Chrysoidine. And, although neither of these colors is as fast to light as the Basic dyes mentioned above, they give very satisfactory results. These colors should be dissolved in water acidified with a little acetic acid.

The greatest pains must be taken in each case to see that the color is all in solution, and that no specks of undissolved color are allowed to come in contact with the leather. The leather must be very carefully and thoroughly moistened by soaking, if necessary over night, in lukewarm water softened, if the surface of the leather seems to demand it, with a few drops of ammonia water.

Dyeing Leather and Staining Leather.—As regards the application of the color; dyers generally make a distinction between leather that isdyed and leather that isstained.

Indyeing leather the moistened goods are placed in a tray or pan (agateware is most convenient for small pieces) and floated backwards and forwards in the dye-liquor, which should be deep enough to fully cover them. The liquor is usually about lukewarm on starting, and may be heated very gradually and gently to about 120° or 130°, if desired. For light shades, however, this is not at all necessary, and indeed the color, as a rule, penetrates deeper and is laid on more evenly when the bath is kept cold. The leather is kept in the dye-bath until the desired shade is reached, which should be at the end of half an hour or so.

When dyed in this manner, the dyestuff has a chance to soak into the leather, and so, when finished, the color is not so liable to be affected by rubbing or by wear. The leather should come out evenly coated on both sides, shaded effects if desired being produced later, by the staining process.

Stained Leather.—In staining leather, on the other hand, the color solution is applied directly to the surface of the damp—not wet—goods by means of a brush or soft sponge, or a little pad of cloth. Accordingly, no matter how carefully the leather has been softened and moistened beforehand, the color does not penetrate far, and is found only on the particular surface where it has been applied.

For flat, even shades, the dyeing process is usually preferable, but by staining, it is possible for the craftsman to work on the surface of the leather, as an artist does on paper with water colors, and beautiful effects can be produced. Oil paint is often used for decorating leather, and when applied skilfully in thin layers, the effects are good. But staining with dyestuffs is usually preferable, as showing more of the grain of the leather, and being more transparent.

The staining of leather may either be done free-hand, or else by the filling in of set designs, marked out previously by tooling or some other method; or, as will be discussed later, by the use of stencils. In any case success chiefly depends upon the condition of the surface that is to receive the dye. The surface of the leather should be dampened, thoroughly and evenly, so that the dye will adhere, and even penetrate a little; but it must not be so wet that the colors will run.

To get this exactly right requires considerable practice. As a rule, the leather is, first, carefully and evenly soaked in water or, if it is at all greasy, in water with a little ammonia in it. When this has been thoroughly done, the leather is taken out and dried off, first on one side and then on the other, with pieces of cloth and then later with blotting paper. After this it is exposed to the air for a little time until the exact point of dryness has been reached.

The color solution should be applied with a camel’s hair brush or a small, soft pad of cotton, and any excess of liquid wiped off, or soaked up with blotting paper, and the color rubbed in with the fingers or pad, as soon as possible.

Acid Dyes for Leather.—As above mentioned, certain shades are hard to obtain without the use of Acid colors. This is particularly true in the case of blue. For the lighter and brighter shades it is necessary to use one of the Acid blues such as Cyanole FF. (Cassella), or Patent Blue (Metz). These are applied in exactly the same way as the Basic colors. Some of the Acid reds, too, will be found valuable for certain shades of scarlet, etc., that can hardly be reached with Safranine. Among the best of the fast Acid colors for leather may be mentioned:

Red.—Fast Scarlet, BXG, Badische; Biebrich Acid Red, 2B, Kalle, and Fast Acid Red, M, Metz.

Yellow.—Tartrazine, Badische; Wool Yellow, 1A, Kalle, and Fast Acid Yellow, 3G, Metz.

Blue.—Wool Fast Blue, BL, Badische; Nerocyannic Blue, B, Kalle, and Fast Acid Blue, BB, Metz.

When using these Acid dyes side by side with the Basic colors, it will be noticed that the latter, as a rule, are far more powerful, and color the leather much more rapidly than the Acid dyes. Accordingly forstaining leather the Basic dyes are the most satisfactory. On the other hand indyeing leather, where the dye-liquor is allowed to act longer on the goods, the Acid colors are more valuable, not only because they are fast to light, but also because they will penetrate more deeply and more evenly.

Finishing Leather.—After coloring the leather it is necessary to finish it carefully, to get a smooth surface and to protect it from injury by rubbing or moisture. Some workers simply let the leather dry and then rub down the surface (without using any wax or oil) with the finger or the palm of the hands. Usually the grain or hair side of the leather is rubbed down with a little wax, the white or yellow wax, used largely as a finishing polish for tan shoes, being frequently employed for this purpose. It can be readily obtained from almost any good shoe store or, if desired, can be made by mixing together equal quantities of beeswax and carnauba wax in a molten condition, and thinning the mixture with a little turpentine.

A recipe used with success by many leather workers calls for a mixture of beeswax, turpentine, and neatsfoot oil. The wax is carefully melted, mixed with a small amount of turpentine, and then enough oil is stirred in to make it soft. When used upon embossed or figured leather this wax is never applied directly, but is placed inside a little bag of soft muslin, and rubbed on and into the leather with a circular motion—the palm of the hand being often used to finish the waxed surface.

Bronze Effects.—An interesting point in connection with the use of the Basic dyes, and some of the Acid dyes, too, for staining leather is that, when applied in a strong solution, as is very likely to be the case when one is trying to get dark shades with an application of the brush or pad, they quite frequently, on drying, show a very marked metallic lustre. This is due to the formation of minute, bright-colored crystals, which reflect the light, thus imparting to the fabric colors which have nothing to do with the shade produced by the dyestuff itself. Thus, Cyanole FF, Cassella, when dissolved, or when dyed on leather or any other material, gives a rather greenish shade of blue. But it gives a very brilliant old gold effect, almost as bright as gold leaf, when applied in a strong solution and allowed to dry quickly.

When this effect is not desired it can be avoided by building up the dark shades by successive applications of weak solution, and by rubbing down the little crystals with, if necessary, a little moisture, whenever they appear to be forming.

In some cases, however, this bronzing property is of some value, and enables the skilful craftsman to obtain interesting and effective results with a minimum of trouble and expense. By painting on a strong solution of dyestuff, and letting it dry quickly, the bronze effect will be produced, and then by rubbing in portions, the true coloring of the dyestuff will be brought out in strong contrast to the crystal-covered surface. Unfortunately, these bronze effects are not fast to either rubbing or moisture, and even dry rubbing will break down the crystals, while rubbing with a damp cloth or a moist finger will dissolve the color off in blotches. To render this bronze effect more durable, it is possible to make a regular bronze lacquer, by adding varnish or gum like orange shellac or gum benzoin to a strong alcoholic solution of a Basic dye. The bronze varnish thus produced will, when dry, stand light finishing with wax in the usual way. The addition of a little benzoic acid to the solution increases the lustre of the crystals.

Chapter XI
SILK—I

So far as we can tell, silk was first discovered and manufactured in China about 1700 B.C., a date corresponding in Biblical history to the time of the patriarch Joseph. From China it was exported to the great and wealthy empire of Persia, and from there was first brought into Europe by Alexander the Great after his defeat of the Persian king. Its origin, although known and described by Aristotle, was for several hundred years a mystery. During the Roman Empire, silken garments, woven in Europe, from Chinese silk imported by way of Persia, were important and very highly prized articles of luxury.

About 555 A.D., while commerce with Persia was interrupted by warfare, two monks in the pay of the Emperor Justinian smuggled eggs of the silkworm and seeds of mulberry trees from China to Constantinople. This was the origin of the European silk industry. It spread rapidly to the various countries bordering on the Mediterranean, and by the seventeenth century was firmly established not only in Spain and Italy, but also in France.

Efforts were made to introduce it, at this time, into England, but without success. In 1622 King James I started the industry, for the first time, in the colony of Virginia in this country. Since that time numerous attempts have been made to develop the American silkworm industry, but with very little success, owing to the large amount of hand labor necessary to produce the material.

At the present time the very finest raw silk in the world is produced in the south of France, and next to that come certain brands of Italian silk. The Japanese silk is more variable in quality, although steadily improving, while the Chinese silk, as a rule, is less satisfactory and more apt to be light and fluffy.

With regard to the consumption, it was estimated that in 1907 Europe used some twenty-five million pounds, and the United States fifteen million pounds of raw silk, which, at an average price of nearly $5.50 per pound, amounted to over two hundred and eighteen million dollars.

Origin and Varieties of Silk.—Silk has been defined as a “smooth, lustrous, elastic fibre of small diameter and of animal origin.” As is well known, ordinary commercial silk is secreted or “spun” by the silkworm, the caterpillar form of a moth known asBombyx Mori, the moth of the mulberry tree. These silkworms have been cultivated for thousands of years, but there exist in different parts of the world, notably in India and Japan, wild or uncultivated silkworms, derived from nearly related, but not identical, families of moths, and whose silk is collected in the forests by the natives, forming what is known in commerce as wild or tussah silk.

Of course, the silk from silkworms, cultivated and wild, is the only one yet produced on a commercial scale. But silk can also be obtained from other animals, notably from spiders and from a peculiar shellfish, the pinna, found in the waters of the Mediterranean.

Silk from the silkworm can be divided into two classes, according to whether the silkworms are the cultivated or the wild varieties. In each case the silk is produced by the caterpillar spinning a covering or shroud, the so-called cocoon, around itself to protect it when in the form of the chrysalis or pupa, awaiting its transformation into the moth.

The ordinary or cultivated silk of commerce comes from worms fed almost exclusively upon the leaves of the white mulberry tree, and cannot be produced successfully without that particular plant. The somewhat similar worms that produce the wild or tussah silks live upon the leaves of the oak, elm, ailanthus, castor oil plant, and others. While the two varieties resemble each other greatly in their chemical properties, they can always be distinguished, because cultivated silk is much more lustrous than the other, but is decidedly less strong.

Tussah Silk, Pongee, Shantung.—The tussah silks, when woven, are commonly known under the general name of pongee. Of late years this name has been applied to imitation goods possessing the characteristic dull color, and even the feel of the real article, but far less strong. These are generally made out of spun silk, derived from “Shappe,” i.e., the by-products of the silk industry, spoilt cocoons, waste from the spinning machines and the dyehouses, and the like—silk, to be sure, but silk of very inferior quality. Accordingly, it is now customary to call real pongee by the name Shantung, after the Chinese province from which much of the wild silk is brought.

Shantung, or true pongee, can be readily distinguished from the imitation by examination of the threads, both warp and filling. These should be very long, and loosely spun or rather “thrown,” whereas the imitation threads are spun together tightly, from fibres of many different lengths, generally quite short.