28.5.22

Silk Dyeing (Continued)

The Craftsman 5, FEB 1909

By professor Charles Pellew, of Columbia University: Number VIII

Skein Dyeing.

When weighting or adulteration is not employed, i. e. in the so-called "pure dye" process, the dyeing of skein silk resembles very closely the piece dyeing described in the last article. The degummed silk is immersed in a dyebath containing the dyestuffs (Acid Colors) dis solved in "boiled-off liquor" slightly acidified with sulphuric acid. The bath is heated nearly to the boiling point and the silk turned in it until the desired shade is produced. It is then taken out, washed thoroughly in water to remove the last traces of acid and then brightened by pass ing through a soap bath with some oil, and later through a bath of weak acid to develop the "scroop." A very important part of the process is the final drying and finish ing. The drying should be done slowly and carefully and not proceed too far or the silk will be brittle. As is well known to dyers, silk has the power of absorbing 25 or 30 per cent. of its weight of water without becoming perceptibly damp to the hand, and this moisture when not carried too far is an actual benefit to the material, making it stronger and more elastic. This property is often made use of by the honest (?) dyer when, in case some of the silk in a lot has been spoiled by accident or carelessness, he makes up the difference in weight by the liberal use of the watering pot.

The finishing process is perhaps the most difficult and technical of all, for the value of the finished product depends very large ly on it and it is almost impossible for an amateur to accomplish it. The skeins, after drying, are hung on a heavy polished wooden bar and with a heavy smooth wooden stick are shaken out, straightened, pulled, twisted and worked until the fibers are all parallel, the kinks taken out, any weak or injured portion cut out and the whole skein has acquired the proper amount of luster.

Sometimes, for especially brilliant fabrics, the skeins are "lustered" by machinery, the so-called "metallic lustering," when the silk, generally enveloped in steam so as to be both hot and damp, is pulled out between two steel arms until it has been stretched a considerable percentage of its original length. This undoubtedly lessens the strength of the fiber considerably and diminishes its elasticity, but under this strain each fiber is stretched out perfectly smooth and thus becomes much more brilliant and lustrous.

Dyeing Silk Black.

The above process, though well suited for quickly producing colors on silk which will be bright and lustrous and, if desired, fast to light although not to washing, is not adapted for blacks. The silk fiber is too transparent and shining to dye a full deep black with any soluble dyestuff. The color, to give really good effect, must be laid on in an insoluble form, either by the use of metallic mordants or by some process of oxidation or condensation. The best that can be done with the Acid Dyes is to give a dark, deep gray, which by itself may look fairly satisfactory, but does not hold its own when matched against a real full black.

The commercial way of obtaining this effect is by the use of the wellknown vegetable dyestuffs contained in logwood. Comparatively few dyers take the trouble to make their solutions from the wood itself, but three or four large companies make a business of preparing and marketing logwood extracts of great purity and uniformity, both in solid and paste form. To produce a black with logwood it is necessary to mordant the silk carefully with iron, tannin and in some processes with salts of tin and of chromium. In all cases, therefore, silk dyed black with logwood contains a certain percentagesay, 1520 per cent. of its weight of foreign ingredients. When carefully done this does no harm to the material and the "pure dyed" logwood blacks are perfectly satisfactory, both for shade, luster and durability.

Weighting of Silk.

Unfortunately, raw silk commands a high price in the market, from $3.50 to $6.00 a pound, and there has been for many years a keen and steady competition between the various dyers and manufacturers to substitute cheaper materials for this expensive raw product. During the last few years this has resulted in the production of the different varieties of artificial silk, concerning which more will be said in a future article. Besides this, however, the dyers and chemists have been straining every nerve to make a small amount of raw silk go a long way by first increasing its weight, and secondly, and as a necessary consequence, materially increasing its bulk by the use of chemicals in the dyeing process.

The first efforts in this direction were based upon the saving of some or, in deed, nearly all of the gum which is wasted in the washing or degumming process previously described. This gum, which amounts to from 25 to 35 per cent. of the raw silk, makes the silk stiff in texture and dull in color, and more difficult to dye. But by modifying the dyeing and especially the finishing process, it was found possible to produce the so-called "souples," i. e. silks with little or no luster, but with the characteristic "scroop" or "feel" and capable of replacing bright silk as a filling in many fabrics and yet with almost all the natural gum left in the fiber.

The black silks were then attacked and an elaborate system of mordanting was introduced before the dyeing proper began. For instance, the silk can be dipped alter nately into solutions of iron and then of ferrocyanide of potash, thus forming Prussian blue in the fiber. Then the excess of iron can be converted by immersion in tannin solutions, such as Gambier or Cutch, into black tannate of iron, or ink, and finally, after perhaps a bath in chromium or tin salts, the final color is brought out by boiling in logwood extract. The silk is then brightened by boiling with good neutral Castile soap, and after drying and finishing the finished product may easily weigh two or even three times as much as the original raw silk did and still retain its strength, luster and elasticity.

The weighting of colored and bright silks did not proceed so rapidly, and it was not much more than ten years ago that by accident some French dyers discovered that by immersion in a strong bath of tin-chlorid (stannic chlorid acidified with some hydrochloric acid) the silk fiber would absorb a large percentage of tin salts with out necessarily losing luster or dyeing power or even strength. This at first was kept a secret, but its use gradually spread until now it is a very poor silk dyer who cannot weight his silk ioo or 150 per cent. without spoiling its immediate commercial value.

Without going into unnecessary details the process is somewhat as follows: The silk, after being degummed and thoroughly washed free of soap, is plunged in a bath of tin chlorid and kept there for some hours. It is then taken out and the loose tin salts are washed off in a tank of water (technically called a box) or in a washing machine. To further "set" the tin, the silk is then placed for a short time in a solution of phosphate of soda and again washed thoroughly. It has now gained from 15 to 25 per cent. of its original weight (3 to 4 ounces to the pound of raw silk). If further weighting is desired this treatment, first in tin chlorid and then in phosphate of soda, can be repeated three or four up to five or even six times, in creasing in weight with each immersion. Then a bath is usually given of silicate of soda, which adds a little weight, 2 to 4 of an ounce, and it is claimed benefits the luster and strength of the goods. Then after a final washing the silk is ready for the dyebath.

The weighted goods are dyed, dried and finished about the same as with the "pure dye" process, and the proud dyer can rejoice at returning to the honest manufacturer from 150 to 250 pounds of finished silk for every ioo pounds of raw silk (containing, by the way, 25 to 30 pounds of gum) which was sent in to the dyehouse.

This "tin-weighting" process is also applied to black dyeing, and enables the black dyer to build up his weight with tin salts instead of limiting him to iron, chromium, ferrocyanide of potash, tannin and logwood.

Properties of Weighted Silk.

It is scarcely necessary to point out that silk weighted to the extreme limit is hardly to be considered as the most durable and trustworthy of fabrics, even when dyed by the most expert workman. Silk dyed carelessly and weighted heavily is less valuable, liable to crack and wear away with the least provocation.

It may be worth while reminding some of my fair readers that the old test of a silk taffeta, "so thick and stiff that it will stand of itself," nowadays is anything but a proof of good quality. One or two manufacturers in this country have during the past two or three years revived the almost forgotten art of making and selling pure dyed goods, and one trouble that they experienced in disposing of their products, outside the high price, was the criticism that their silk felt so light and thin.

Tests for Weighted Silk.

At present it is almost impossible, at least in New York, to buy puredyed heavy silks. The writer, at any rate, tried hard this last autumn to find for some special experiments a piece of white taffeta which was not markedly weighted. After visiting not only depart ment stores but the very best dry-goods stores in the city, at all of which he was informed that no such material now existed, the best he could do was to find one make of silk where the organzine or warp was fairly pure, the tram being well weighted. Lightweight Japan and China silk dyed in the piece can still be procured with little or no weighting.

The test, known to all buyers in the trade, is a simple one. The threads of silk should be pulled and combed out, separating carefully the warp from the filling, and each of them touched with a lighted match. Pure silk burns fast and freely to the end, leaving little or no ash, while weighted silk burns slowly, leaving much residue, and if heavily weighted will not carry the flame at all.

The chemical analysis of weighted silk is not very satisfactory, and in general can hardly be made, excepting by a chemist expert in silk dyeing and weighting as well as in ordinary analytical methods.

Silk Dyeing by Amateurs and Craftsmen.

It is hardly necessary to point out that the above processes need skilled dyers and chemists to produce satisfactory re sults.

Craftsmen can, however, get quite satisfactory results by "pure dyeing" piece goods and even skeins with acid dyes, in a soap bath acidified with a little sulphuric acid, as described in the last article, although it is hard to finish the skeins with out instruction from a professional.

The Acid Dyes, however, are not always satisfactory on account of their behavior to moisture. The best ones are exceedingly fast to light and the range of shades is great, but the colors strip entirely and easily in hot soap baths, and, which is more objectionable, they generally bleed and stain when wet with even pure water.

Colors faster to washing, although not as a rule so fast to light, can be readily obtained by using the Salt or Direct Cotton Dyes, described in the August number of the Craftsman; these dye silk readily in a soap bath with the mixture, first, of a certain amount (three or four times as much as of the dyestuff) of salt or Glauber's salt and later of a little acetic acid. Silks dyod with these Salt Colors are "fast" but not "embroidery fast" that is, they will not stain in water or with light soaping, but cannot be put in the washtub and boiled with cotton goods without bleeding and staining the white goods.

To stand the latter test, the simplest method is to dye the silk with the Sulphur Dyes previously described, care being taken to avoid tendering the silk with the strong alkali of the sodium sulphide. To protect the silk from this it is necessary to use as little sodium carbonate and sulphide as possible, consistent with dissolving the dyestuff. Then, by using a large excess of dyestuff, the silk need be immersed for but a short time, and finally various chemicals can be used to protect the fiber.

Glucose is often used for this purpose. But, for full shades, the best way is to add sodium bisulphite to the bath, containing dyestuff and sodium sulphide, until the liquid is just about neutral.

To get the best results the reaction of the bath should be tested in the manner known to all chemists, with an alcoholic solution of phenolphthalein. This solution is colorless in the presence of acids or even when neutral, but turns pink or red with the least trace of alkali. After the dyestuff, dissolved in hot water with so dium sulphide and sodium carbonate, has been put in the dyebath, a solution of sodium bisulphite is added, little by little, stirring well until a drop of the liquid, spotted on a piece of blotting paper and touched with a drop of the phenolphthalein, remains colorless for a minute or two and then turns a light purple. If the purple color does not develop at all the bath is too acid and needs the addition of a little more sodium sulphide. If the color appears at once the bath is too alkaline, and more of the bisulphite should be added.

In a bath made up in this way silk can be warmed with impunity and by the use of plenty of dyestuff and the addition of two or three tablespoonfuls of salt to the bath after the dyeing has proceeded for some little time, full deep shades can be produced, which, after exposure to the air to oxidize them, can be washed in boiling soap baths without running or fading.

Of course, for lighter shades the bath need not be neutralized with so much care. Bisulphite should be added to diminish the alkalinity, and then the silk dyed as quickly and with as little heating as possible.

Black Dyeing for Craftsmen.

The process just described is of still greater importance as a means for getting satisfactory blacks on silk without the long, tedious, complicated and difficult process of logwood dyeing. Excellent sulphur blacks are on the market which will give very fair results even to the amateur dyer, and which offer the decided advantage of dyeing cotton and linen fibers in the same bath quite as deeply as they do the silk.

Of course, to get full shades of black, great care must be taken to have the bath the exact degree of alkalinity, and to get the full strength of the dyestuff. A good dye for this purpose is Thiogene Black liquid M.pat (Metz) for the use of which this process was patented.

Besides the Sulphur Colors, dyers some times use some of the Alizarine Colors, and, especially, of the new Salt or Direct Cotton Colors suitably fixed, for the production of blacks without the use of logwood.

The Alizarine Colors properly mordant ed give excellent shades on silk as well as on wool and cotton, which are among the fastest colors known both against light and washing. Their use, however, is too complicated to be of much value to craftsmen.

During the last three or four years the Salt Colors have been coming greatly to the front, and not only are used for colors but also for blacks upon silk with considerable success. To obtain a really good black it is necessary first to dye the silk thoroughly, as before described, with one of the Salt Colors, and then to fix it by the so-called diazotizing and developing process. This, however, is rather too delicate a chemical process for the average craftsman, and hence it hardly needs describing here.

Dyeing Silks.

Craftsman 4(?), 1909

By professor Charles Pellew, of Columbia University: Number VII

Some of my readers may have noticed that in the last article, on the Acid Dyes, no details were given about the dyeing of silk, although this fabric, along with wool, feathers, and other animal fibers, is almost universally dyed with colors belonging to this class. But silk is such an interesting and important textile and so unlike, in composition and character, all the others, that it has been thought advisable to devote a Trial article to its preparation and structure before touching on the dyeing.

Definition - varieties of silk

Silk has been defined as a "smooth, lustrous, elastic fiber of small diameter and of animal origin." As is well known, the ordinary silk of commerce is secreted or "spun" by the silkworm, the caterpillar form of a moth known as Bombyx 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 tussore silk.

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

Silk from Spiders.

For a couple of hundred years it has been known that in certain tropical and semitropical countries spiders were found of such large size that their webs would furnish a fiber strong enough for textile purposes. In Paraguay and in Venezuela silken fabrics have been made in this way on a small scale for a long time.

During the last few years a similar industry has been started in Madagascar by the efforts of a French missionary, who invented a simple apparatus for confining the spiders and for extracting silk from them in fairly large quantities. The large spiders used for this purpose are extremely abundant in the forests and parks on that island.

The factory, as it was finally fitted up on the very edge of the forest, contains workshops for the spiders in the form of a large number of little pigeonhole cells, in which each insect is carefully shut in by a wooden guillotinelike holder, which fastens around its body, exposing the abdomen and separating it from the legs and head. The operators (native girls with very delicate, light fingers) then proceed to tap these spiders, drawing the silk from them by pressing them until the gummy mass exudes, and then drawing it off in fine threads and joining it to others which, together, are reeled off by a small wheel until the supply from the individual spider is exhausted. It is claimed that if carefuly treated the spiders are not injured by this process and if well fed can be tapped four or five times a month, giving some thousands of yards of silk each time. The thread thus formed is of a bright yellow color, extremely strong, and very brilliant and lustrous. It has been woven into cloth, making very beautiful material; and at the Paris Exposition in 1900 a piece of spider silk was shown, 18 yards long and 18 inches wide. Unfortunately, on the side of a commercial success, to produce this cloth some 25,000 spiders were required and it is estimated that the silk cost from $30.00 to $40.00 a pound. It is hoped that with experience the cost may in time be lessened until this silk can compete with ordinary silk on fairly equal terms.

Silk from the Silkworm.

As before mentioned, this can be divided into two parts, 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 silk of commerce all conies from the worms of the moth known as Bombyx Mori, which during thousands of years has been studied and grown for this purpose. These worms feed upon the leaves of the white mulberry tree and cannot be successfully cultivated without that plant. The somewhat similar worms producing the various wild silks, or tussore silks, of commerce, live upon leaves of the oak, ailanthus, elm, castor oil plant and others.

History.

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 to 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. Its cultivation spread rapidly to the various countries bordering on the Mediterranean, and by the 17th 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 much success, and 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 comes 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 twentyfive million pounds and the United States fifteen million pounds of raw silk, which at an average price of nearly 85.50 per pound amounted to over two hundred and eighteen million dollars.

It is universally agreed that the United States consumes more silk than any other country in the world. in 1906 the importations of raw silk into the country amounted to nearly sixty-five million dollars; of spun silk, over three million dollars, and of waste (cocoons, etc.) over one million dollars, making a total of sixty-nine million dollars. Besides this here were imported of manufactured goods over thirty-four million dollars, making the total importations for the year well over one hundred million dollars.

Preparation, Manufacture of Silk.

The full process of manufacturing silk, from the silkworms to the shop, may be divided into the following steps:
(1) Raising of the cocoon,
(2) Reeling or filiature.
(3) Throwing the raw silk,
(4) Stripping, weighting, dyeing and finishing the skeins,
(5) Weaving and finishing the fabric.

Raising the Cocoons.

The eggs collected from the moth are spread out on cardboard, kept warm and damp, and in to to 12 days hatch out into minute worms. These are freely fed with mulberry leaves and grow very fast, until at the end of four or five weeks they arc full grown and ready to spin. They are then transferred to wicker baskets, and proceed to fasten themselves to the walls at convenient places, and then to gradually enshroud themselves in a fine, closely woven web or cocoon by continuously pressing from the silk glands in their heads a thick, gummy fluid which hardens in the air.

This operation takes about five days, after which the worm changes to the state of pupa or chrysalis, and rests immovable inside the cocoon until after some fifteen or twenty days it changes to a moth. It then proceeds to eat, or rather dissolve by means of an alkaline secretion, its way out of the cocoon, cutting through the threads to such an extent that the silk is useless for reeling purposes, and can only be used for carding and spinning. Accordingly, only enough cocoons are allowed to ripen to furnish a new crop of eggs; the rest are carefully baked, so as to destroy the pup contained in them.

Reeling the Raw Silk from the Cocoon.

The amount of silk obtained from each cocoon is but small, and much of it is in the form of floss or waste, useful only for spinning. So it takes from two thousand to three thousand cocoons to furnish one pound of raw silk. The silk is reeled off by hand, after soaking the cocoons in warm water to soften the gum which fastens the fibers together. The threads from several different cocoons are combined by the operator into one continuous fiber, which is reeled off gradually, and as fast as one thread breaks or comes to an end another one is thrown in from another cocoon.

This furnishes the raw silk of commerce and consists of two different compounds. The most important is the fibroin or silk fiber, which is strong, elastic, with brilliant luster, insoluble in water and dilute acids, but readily soluble in alkalies, especially if hot and strong; but besides this, it contains from 30 to 45 per cent. of sericin, or silk gum, which is stiff and brittle, without luster, and, while softening in warm water, dissolves readily in hot soapsuds or warm alkaline solutions.

Throwing the Silk.

Silk differs from cotton, wool, linen and other textile fibers by being made of one continuous thread and not of a series of short threads which have to be twisted tightly together before they can be woven. So, instead of a spinning process, the raw silk is subjected to what is known as "throwing," in order to make the thread suitable for dyeing and weaving. For this purpose the raw silk is softened in hot water and soapsuds and several threads are combined together by twisting and supposition and reeled off into one thread of thrown silk.

Two main varieties of thrown silk are universally recognized in the trade. namely, organzine and tram. The organzinc is the thread used for warp. It is very strong and tightly twisted, with, as a rule, considerable luster. In some kind of weaving the luster of the material depends entirely upon the warp. The tram, on the other hand, constitutes the filling. It is usually more loosely woven, of thicker thread, and need not be either so strong or so lustrous. It is usually made of from two to five threads of raw silk and, of late years, has been generally greatly adulterated.

While this thrown silk has lost some of its original gum, it still contains some 2030 per cent. of sericin, or gum, which prevents it from having any luster, makes it hard to dye, and causes it to be too stiff for weaving.

Stripping or Degumming the Silk.

To extract this gum, the silk, still in skeins or hanks, is heated for some hours in a strong solution of (neutral) soap, and then washed well in other soap baths and in hot water until it is perfectly soft and has gained the proper luster. The soap containing the gum thus extracted, called `boiledoff liquor" or "soap gum," is carefully kept and used in dyeing colors.

After stripping, there are two lines of treatment, according to whether the silk is to be "piece dyed" or "dyed in the skein."

In piece dyeing the stripped silk is passed through a weak bath of acid, usually acetic acid, and then woven into goods of the desired quality. These goods are then dyed in the piece by being run through the dye bath until they are of the proper shade. The dye bath (for colors) is made by stirring the proper quantity of acid dyestuffs, the same as those mentioned in the last article, into a bath of boiledoff liquor, which is faintly acidified, or "broken," as the technical phrase goes, by the addition of some sulphuric acid. This boiledoff liquor has the property of laying the dyes on the silk evenly and thoroughly and is better for that purpose than any other medium. For amateur work, or where boiledoff liquor cannot be obtained, very fair results can be obtained with a strong bath of olive oil soap (Castile or NI arseilles soap), made acid with dilute sulphuric acid.

The term "breaking" the soap bath is very significant. The acid should be added drop by drop to the frothing soap bath until the bubbles disappear and a thin iridescent film of fatty acid rises to the top of the liquid.

After the piece goods are brought to the proper shade, they are then finished, usually by carefully rinsing in water to take away all traces of free acid, then by passing through a cold soap bath, often with a little olive oil emulsified in it, to increase the luster, and finally through a bath of weak organic acid, like acetic acid, to develop the so-called "scroop" or "feel" of the silk. When silk is washed in soap, or, especially, in even a weak bath of alkali, it becomes soft and clammy to the touch, and has no "life" or "snap" to it when dry. The passage through even a weak bath of acid develops the characteristic stiffness of the silk fiber, and causes it to give the peculiar rustling sound when pressed.

Skein Dyeing.

The silk dyers proper, who dye and finish their silk in skeins before weaving, consider the above process as very inferior, in skill and in results, to their own art. It is true that piecedyed goods arc usually rather light and thin in quality, and not, as a rule, as lustrous as the others, while they can only be produced in solid colors, or with patterns stamped or printed upon a background of solid color. On the other hand, it is much more difficult to heavily adulterate and weight piece-dyed goods, and hence the lack of weight has compensating advantages.

The treatment of silk in skeins has been developed to a high art by the skill of dyers and chemists throughout the world, and is not infrequently referred to as one of the triumphs of modern science. Whether the chemist who makes two pounds of silk appear from one, or far less than one, pound of raw material is entitled to quite the same rank, as a benefactor of the human race, as the scientific agriculturist that we have so often heard about, is perhaps open to question. But the products of his skill and labors are met with everywhere and I propose in the next article to discuss his methods with some detail.

27.5.22

Dyes from Camphor.

Manufacturer and builder 4, 1880

Dr. W. H. Gregg, of Elmira, N. Y., is reported to have succeeded in obtaining a new coloring principle from camphor, to which he gives the name of "Laureline." Thus far he has only succeeded in producing various shades of yellow from it; but he is reported to be engaged in certain experiments which he hopes will result in the production of carmine and scarlet. The chief feature of the new dyestuff which recommends it to the attention of textile manufacturers, is in the brilliancy and fastness of the colors.

It can be used upon linen, cotton and silk with no apparent difference in density and brilliancy, and goods thus dyed are said to be entirely unaffected by the ordinary tests to which they will be subjected in use. Boiling for hours in a strong soap solution barely turned the shade of a cotton sample. With indigo, a handsome green is produced.

The inventor is not yet prepared to give special details respecting the cost of producing the new dye, or of the precise methods of using it; but as regards the first item, he intimates that it will be one of the cheapest, and as to the second, one of the simplest coloring matters to make and apply. The textile journals speak in terms of great interest of the new discovery.