ARTIFICIAL SILK
History.—The famous old French chemist, Réaumur, in the year 1734, suggested, after a study of the silk worm, and of the method by which it “spins” the natural thread, that it might be possible to make a jelly-like substance which could be drawn out into a fine thread and, coagulating, form an artificial silk.
This suggestion was first acted on, in a practical way, in the year 1855, when Andermars obtained some curious results by dipping a needle or fine metal rod into a thin viscous solution known as collodion, and then drawing it out rapidly, made fine, smooth threads as the material solidified. This collodion, which for many years has been in common use in minor surgery to paint on wounds and cuts, because it leaves a film of artificial skin, and in more recent times has been much used in photography, is a solution of gun cotton or nitro-cellulose in a mixture of alcohol and ether. In 1885 Count Hilary de Chardonnet made improvements in this last process, and produced successfully the first real artificial silk threads on a commercial scale.
Chardonnet Silk.—He also used a thick collodion solution, but instead ofdrawing it out hepressed it out through fine holes by using very great pressure. As fast as the gummy thread exuded it was picked up, carried along into a drying room, where the alcohol and ether could escape (to be condensed later and used over again), and then the solid fibre was passed into a solution of some suitable reducing agent, such as ammonium or sodium sulphydrate, which converts the inflammable gun cotton into its original condition of cellulose. These resulting threads, being smooth and uniform when properly made, have very great lustre. Indeed, they are often far more brilliant than the very best and finest natural silk, and can be dyed and woven into beautiful fabrics.
This discovery of Chardonnet’s was at once utilized, and large and flourishing factories of Chardonnet silk sprang up all over Europe. The first large factory, which is still doing a very profitable business, was at Besançon, in France, and later a large factory was established at Frankfort, Germany.
Pauly Silk.—The success of this process aroused the interest of other chemists, and before long several rival processes came into existence, also based on the use of a viscous solution of a cellulose compound. One company, making the so-called Pauly silk, utilized the solvent action of an ammoniacal copper solution upon cellulose for their starting point.
Elberfeld Silk, Glanzstoff.—The Farbenfabriken von Elberfeld, famous manufacturers of dyestuffs, took up the manufacture of silk from a solution of a compound of cellulose with acetic acid; and the Elberfeld silk, or, as it is widely known in Germany, Glanzstoff, is every year becoming a more and more important factor in the silk business.
Viscose Silk.—A still different process, which during the past two or three years has been successfully introduced into the United States, depends upon the curious substance called Viscose, a thick, sticky solution of cellulose made by first treating wood pulp, cotton or other vegetable fibre with strong caustic soda and then dissolving the resulting product in carbon disulphide.
This Viscose was first introduced for many different purposes. The solvent, carbon disulphide, is very volatile, and flies off readily, leaving the cellulose behind in the form of a stiff jelly which, on drying, becomes solid and strong. So Viscose was used for water-proofing paper, etc., for making solid articles like piano keys and billiard balls, and even for making opaque patterns in calico printing. But its most valuable application is for artificial silk. It is pressed out through fine holes, and the thread resulting quickly solidifies as the solvent evaporates, and can be dried carefully and worked up on reels or bobbins, to be dyed later.
Properties.—Artificial silk, as a rule, is a little stiffer than natural silk, but has an exceedingly fine lustre. It cannot be spun in as fine threads as fine, natural silk, but, on the other hand, can be produced in thick, smooth threads which, stained as a rule black or dark colors, quite replace horsehair for furniture coverings, etc. Similar products are made, too, by coating cotton with a layer of artificial silk.
Another curious use of this artificial silk process is when it is formed into still larger threads, very lustrous and quite stiff, and used for plumes and aigrettes. They can be dyed any color, have excellent lustre, and are extremely useful for millinery.
Precautions Necessary in Dyeing.—One great drawback is common to all these different varieties of artificial silk. They are quite strong, although not particularly elastic, when dry, but when wet lose their strength very markedly. Indeed, at one time it was found extremely troublesome to dye them, as the silk skein dyers, accustomed to work and wring and stretch their silk, with impunity, in and out of the hot dye-baths, would try the same treatment with this new product, and in consequence ruin every skein. When thoroughly wet through in a hot bath the thread will soften until a skein may hardly bear its own weight. Accordingly, the dyeing is always done as quickly as possible, and generally at a lukewarm or only moderately high temperature. The skeins should be handled as little as possible in the dye-bath, and, when taken out to wring, should be rinsed slightly to get rid of extra color, acid, etc., and then carefully dried, not by twisting on two sticks, as is customary with other materials, but by wrapping in cheese cloth or blotting paper and then running the skeins backward and forward through the clothes wringer.
Tests for Artificial Silk.—It has been ascertained that all varieties of artificial silk now on the market are made from some form of cellulose. Efforts have been made to take thick jellies made from gelatine or similar animal compounds, and make threads from them, coagulating them later by treatment with formaldehyde or similar chemicals.
These experiments have, however, not as yet proved successful. Accordingly, any test that will distinguish between a vegetable and an animal fibre will show whether a brilliant thread or piece of textiles contains natural silk or not. The simplest of tests is, of course, to burn a little with a match or at a flame and see if there results the characteristic “burnt feather smell” of charring animal tissues. This odor accompanies the natural silk. The chemist would probably make the same test more accurately by heating a wad of the material in the bottom of a small test tube and noticing whether ammonia was being evolved, and whether the distillate was alkaline in reaction. The ammonia and alkali resulting from the nitrogenous organic matter is a certain indication of animal matter.
To distinguish between mercerized cotton and artificial silk, it is generally enough to soak the samples for a short time, say a quarter of an hour, in boiling water and test their strength. Mercerized cotton properly made would be just as strong afterward as before, while the artificial silk would be soft and weak, if it would not, indeed, break down completely. Besides this, it must be remembered that the mercerized cotton, in spite of its lustre, is made up of threads tightly spun together from a large number of short fibres, none of which are over two inches or so in length, while the artificial silks are made up, like the natural silk, of long, continuous fibres twisted together to form the yarn.
In general, these artificial silks, manufactured as they are from wood pulp and other vegetable materials, are to be dyed with the Salt, Sulphur, or Vat dyes, care always being taken to expose them to the action of hot dye-liquors as short a time as possible. The Salt dyes are less apt to interfere with the brilliant lustre, but the Sulphur and Vat dyes have the great advantage of dyeing in a cold or lukewarm bath, without any loss in fastness.
The Chardonnet silk has a special affinity for the Basic dyes, and in the trade is usually dyed both light and dark shades with these coloring matters, without previous mordanting, in a slightly acid bath. This practice, however, while simple and easy, is not to be recommended. For the Basic dyes, with but few exceptions, fugitive under all circumstances, are particularly sensitive to light, when dyed in light shades, upon such a brilliant and almost transparent medium as this is. On the other hand, articles made of artificial silk, being easily injured by rain, are not so liable to be exposed to the open weather as some other less delicate materials.
The Viscose and Elberfeld silks (Glanzstoff) have less affinity for the Basic dyes, and dye more readily with the Salt and Sulphur colors than the Chardonnet silk, made from gun cotton. But it is perfectly possible to dye the latter also with fast colors of the Salt, Sulphur, or Vat classes, providing large amounts of dyestuff are used to bring up the shade. Indeed it is poor economy to be sparing of the coloring matter, when working with any kind of artificial silk. For speed is essential, and the dyer who lets his material remain long in the dye-bath is liable to get into difficulties.
The artificial silk, after dyeing, should be finished much like natural silk, by rinsing and then passing through a bath containing some olive oil, emulsified in a weak bath of soda ash. This increases the lustre. It should also be dried at a fairly low temperature and, while drying, kept stretched out by hanging a wooden or glass rod in the loop of the hanging skein, or some similar device, taking care to avoid strain great enough to pull apart the weakened fibre.
When dyeing this material great care should also be taken in tying up the individual skeins and in handling them. Turn them in the dye-bath as little as possible consistent with even dyeing. The threads, unless very tightly spun, are constantly liable to come untwisted, and the knots to untie, causing much annoyance.
In conclusion, when carefully made and dyed these artificial silks furnish beautiful, brilliant, lustrous fibres, which can be used to great effect in many kinds of handicraft work. They can easily be procured with more lustre than the very best natural silk, but even when dry are deficient in elasticity, and to some extent in strength, and when wet are very fragile. The price is kept at a rather high figure, as a rule only from 25 to 50 cents a pound less than that of good natural silk. But every year the production is increasing, new factories are springing up in every country, and as there is no limit to the production excepting the demand, it is probable that in a few years, thanks to competition, the price will be dropped very considerably and the whole silk business will be revolutionized. At present it is estimated that the production of the artificial silk is not far from one-fifth that of natural silk, and this fraction is getting larger every month.
Indeed, the rise of this particular industry may fairly be considered as one of the most interesting, most useful, and most valuable contributions of the manufacturing chemist during the last quarter century.
Chapter XIV
TIED AND DYED WORK
Hitherto, in this book, the student has been instructed in the general art of dyeing and coloring the various fabrics, both in the yarn and in piece, without any attention to the subject of coloring them in patterns or designs. The remaining chapters will be devoted to various methods, suitable for craftsmen, by which the dyestuffs can be applied so as to give more or less definite patterns to the objects to be colored.
This art, in its general principles, was worked out in various parts of the world at very early periods in their civilization. In a great many cases colored designs in textiles were formed, in the process of weaving, by incorporating yarns of different colors in certain portions of the fabric.
But along with this, at a very early stage in the textile industry, there was developed the art of making patterns, regular or irregular, by the action of dyestuffs upon previously woven goods. In general there are three methods for doing this which, it is claimed, were known to the ancient Egyptians just as well as they are to the modern calico printer. These three methods are known as Direct Coloring, Discharge, and Resist dyeing.
FIG. 2—TIED AND DYED HEADDRESS FROM AN INCA TOMB IN PERU
Direct Coloring.—This means the application of the dyestuff or coloring matter to different special portions of the textile or fabric, so as to give a colored design, upon a lighter background. The dye may be applied by dipping special portions of the fabric into it, in which case the pattern is apt to be a very loose and irregular one. Or, if the material will take the dye readily enough, as for instance in the staining of leather, it may be applied with a brush, or a small pad.
More formal and intricate designs can be made by applying the color in the form of a paste, through the help of stencils, as worked out by the Japanese so beautifully, or by means of wooden or metallic blocks, as in the block printing in the East, which in Europe and America has developed into the art of calico printing, by rolls run by machinery.
Discharge.—This process is the exact reverse of the preceding one, in that the cloth or other material is dyed first, and later the color is either entirely removed or, it may be, very decidedly altered in shade, in certain special parts, by the application of some chemical.
The earliest examples of this are where cloths stained with Iron buff, have had patterns made in them by washing out certain portions with acid. Just as some of the earliest forms of “direct coloring” are shown in the dark patterns of leaves, formed by the same Iron buff dye, upon cloth against which moist fresh leaves have been crushed.
The discharge process is not as commonly used by craftsmen as the other two methods, because it has not always been easy to find or to use a chemical that will properly destroy or change any particular color, without at the same time, if fast dyes are used, destroying or at least injuring the fabric. The professional dyer, working in conjunction with the chemist, carefully weighing the reagents, and using steam chests and drying chambers with definite and carefully regulated temperatures, can fully discharge even the fastest dyes without danger. But this is difficult, if not impossible for the craftsman, and while the process will be discussed and described under the subject of stencilling, it will be found, comparatively, of but little practical importance.
Resist.—The third and last method for getting colored patterns is one which has been used in different ways, by the most widely scattered nations, and which, to this day, furnishes one of the most interesting and important processes at the disposal of the craftsman, as opposed to the professional dyer.
It consists of applying to certain portions of the fabric, before dyeing, some agent which, acting either chemically or mechanically, will “resist” the action of the dyestuff at the places where it is applied. These parts accordingly will remain in their original color, or at any rate will be but slightly colored, while other portions, not so protected, will be dyed full shades. This, in many respects, is the most advantageous way of obtaining patterns for the craftsman, because no action has taken place tending to injure the strength or durability of either material or dyestuff, and as the color is applied in a regular dye-bath there is generally an opportunity to apply the dyestuffs in the most approved manner.
Variations in Resist Work.—The resist method has been discovered in many parts of the world, and has been carried out in many ways. In Java, for instance, a beautiful art was developed known as Batik, to be described later, in more detail. These people used, as a resisting medium, molten beeswax, which could be poured or painted on to the cloth wherever desired, and, according to whether it was applied hot or only just warm enough to be liquid, would protect the material covered, either wholly or partially, against the action of dyestuffs in a cold bath.
Less elaborate, but still very interesting processes are reported from many other quarters. As will be described in the next chapter the Japanese have long used a resist paste, to make white patterns against dark backgrounds with their stencils. In some of the Pacific Islands natives have learnt to make patterns by pressing pieces of cloth tightly between shells, as for instance the two halves of a clam shell, and then dyeing or staining around them. Other tribes learnt the trick of tying or sewing flat thin pieces of wood together, tightly compressing the cloth between them and thus preventing the dyestuff from reaching those parts of the goods when dyed later.
But the most common process, and one which is not only the simplest and easiest to carry out, but also offers to the skilful dyer an almost unlimited range of interesting and effective results, in color and design, is the so-called “Tied and Dyed Work.”