Application of Dyestuffs To Textiles, Paper, Leather and other Materials

1. General Definitions - The term dyeing is used almost exclusively with reference to the textile industry, and it is in this sense alone that it shall here be employed. Dyeing means to impart to the fibrous substances, fabric, yarn, or other textile material, a color which shall possess certain qualities, among which may be mentioned uniformity and stability towards washing, exposure, etc. As textile materials are composed of various fibers, dyeing really refers more especially to the coloring of the fibers of which the textile consists. The chief fibers which find an extensive -application in the manufacture of textiles are wool, silk, and cotton, and as the methods of dyeing these fibers are radically different,, it becomes necessary to classify the study of the phenomena of dyeing under the separate subjects of wool dyeing, silk dyeing, and cotton dyeing.

Dyeing, in the proper sense of the word, has a deeper meaning than that of merely imparting a color to the fibers; the color must be uniformly distributed throughout the substance of the fiber, and not merely be a coating on its surface. The latter would be classified under the term of painting and not dyeing.

In order that the color shall penetrate into the substance of the fiber, the coloring matter must be applied in the form of a solution. Herein lies the difference between dyestuffs and pigments; the former are colored bodies of a soluble nature, usually complex derivatives of carbon, whereas the latter are insoluble and mostly of mineral origin. But all soluble colored substances are not dyestuffs; a solution of copper sulphate, for instance, possesses a deep blue color; potassium bichromate in solution has a deep orange-yellow color; if wool be saturated with these solutions, it will acquire a blue or a yellow color, as the case may be, but this color can be readily' removed by washing with water, and we do not consider the wool as being dyed, the color in this case only being due to the fact that some of the colored solution is for the time being retained in the interstices between the fibers. A solution of Magenta possesses a beautiful bluish red color; if wool be impregnated with this solution, it will acquire a similar color, and this color will persist after even a long-continued washing, and the wool is said to be dyed by the Magenta. In this latter case the particles of coloring matter have become fixed in the substance of the fiber in an insoluble form, so that it cannot be removed by simple means.

The wool is said to possess an " affinity " for the dyestuff-in other words, it combines with the coloring matter and becomes permanently dyed thereby. It is plain that neither the copper sulphate nor the potassium bichromate would be called a dyestuff, whereas Magenta would be so designated. A dyestuff, then may be defined as a soluble substance capable of imparting a permanent color to the textile fibers.

So far, the subject of dyeing includes two objects for our consideration, namely, the fiber and the dyestuff. The process of dyeing, however, is rarely so simple that it consists only of impregnating the fiber with a solution of the dyestuff; there are other essentials which must be considered. Various chemical agents have to be employed in connection with most of the dyestuffs to yield the proper results, and the nature and action of these have to be understood in order to have a clear insight into the process of dyeing. The study of dyeing is really a specialized branch of chemistry; for not only are the processes themselves more or less chemical ones, but a knowledge of the various materials employed is essentially a knowledge of chemistry. Dyeing as a science, then, is but a branch of applied chemistry which has for its subject the study of the fiber, the dyestuffs and other necessary chemicals, as well as the chemical reactions by which the process is carried out.

Textile printing is really a specialized department of dyeing in which the color is applied to certain portions only of the fabric, usually with certain definite pattern effects. The processes in the main are about the same as in ordinary dyeing, the chief differences consisting in the mechanical methods employed in applying the color. The same is also true of the many special methods used in fancy dyeing, such as spray dyeing, batik, tie-dyeing, stencil dyeing, etc. The nature of the fundamental operations in all cases is the same.

Mention of the latter methods of using dyestuffs for ornamental and decorative purposes brings up the question of craft dyeing, or what might be termed the artistic use of dyes and processes of application to produce special objects of beauty and artistic value. The ordinary dyer in the mill or dyehouse is primarily concerned only with the proper production of a certain color on so many yards of cloth or so many pounds of yarn or loose fiber. His chief problem is the matching of shades, and the obtaining of a uniform color of certain specified qualities of fastness at the minimum of cost. The craft dyer, on the other hand, works with an entirely different purpose in view. He (or she) endeavors to produce colors and color combinations on a fabric more with reference to the particular use of the material being dyed, and at, the same time trying to put into the work some form of artistic expression, using the color as a component of design. The ordinary dyer, then, is merely an artisan, while the dye-craftsman attempts to be also an artist.

In ancient and medieval days, when the division of labor was not so finely adjusted as at the present time, the dyer was more closely in contact with the finished article that his work helped to decorate, and in consequence he was more a craftsman and artist than at present. Craft dyeing in this country has received an awakened interest on account of the European War, which brought about a wide interest in the manufacture of dyestuffs on this side of the Atlantic. Owing to many fancy textiles from Europe being taken out of trade by the war, there was an opportunity in this country to develop various lines of artistic dyeing in a market free from European competition, and as a result this form of craft has been able to get fairly well established.

Dyeing in the batik style of applying the color to design has been undertaken by a number of color artists, and very laudable and excellent work has been turned out. It is also true that a number of amateurs and half-baked artists have entered this field with little or no knowledge of the possibilities of dyeing and with little or no skill in technique or ability in design, and as a result they have turned out some horrible examples of bad taste both in form of design and in combinations of color. Originality of idea and highly developed skill in technique are just as essential in producing good results in this form of color art as in painting or other form of art expression.

The batik style is generally applied to cloth for a specific use in a special garment or decorative fabric, and the design and color effects are' adjusted to meet the requirements of the particular piece. For example, this method of dyeing is applied largely to silk goods used in making ladies' waists or gowns; in scarfs, draperies, and hangings for purposes of interior decoration, etc.

The tie-dyeing style is also employed both by itself and in connection with batik for the same purposes. Like batik, tie-dyeing also requires a skillfully developed technique of handling in order to obtain proper results, otherwise very crude designs will be produced. As both of these styles often require the dyeing of one color over another, the operator must have an intimate knowledge of such color combinations in order to obtain the proper artistic effects. Also -in tie-dyeing considerable ingenuity has to be exercised in forming ties in the cloth which will yield harmonious and properly balanced designs; this requires an originality of handiwork which usually takes considerable experience to develop. The mistake is often made by the amateur that any odd effect is artistic, but this is far from being the case. Just what constitutes an artistic effect is perhaps very difficult to describe, and no doubt the difference between good taste and bad taste is instinctive and can be cultivated only through experience.

The field for craft dyeing in this country is a broad one, and there is a large and appreciative public ready to absorb real artistic productions at a price which is helpful in developing and encouraging the art. On the other hand, this form of craft has a strong appeal to the dilettante and egregious amateur, with the result that there is danger of a flood of poorly executed and badly designed productions submerging the really good things in this line. As a rule, textile and color chemists, as well as the expert colorists of the dyestuff factories, have given little or no consideration to these possibilities in craft dyeing, believing it to be too small and unimportant a line on which to waste time and labor. This may be somewhat true if the quantity of dyestuffs consumed is taken as a measure of its importance, for in this respect craft dyeing uses a very small proportion of dyestuffs in comparison with the regular lines of dyeing. It deals more with the dyeing of goods by the square foot than by the thousands of yards, and probably the country's entire consumption of dyestuff in craft dyeing would not equal that of one moderately sized dyehouse or mill. But, on the other hand, the color chemist as well as the dyestuff manufacturer should realize that in craft dyeing we have the possibility of reaching into realms of color art that is not present in ordinary trade dyeing. There is also the germ of originality and creative purpose that may lead to yet undiscovered fields in dyeing, that may eventually widen out the application and use of dyestuffs in general.

As a background to the main province of dyeing, it is well to develop and encourage this matter of craft dyeing as far as possible, and the color chemist and dyestuff producer should give it their serious attention. To the chemist it should prove an attractive field in the devising of ingenious methods of applying dyestuffs and mordants to produce effects by hand treatment that are hardly thought of by the ordinary dyer. And there is, always the possibility that many of these processes may be adapted subsequently to a large-scale production that will give results of a higher degree of quality and taste.

2. Historical. - Considered from an historical point of view, dyeing is as old as the textile industry itself, and this antedates the written documents of human history. Closely connected with the utilitarian desire of human beings to clothe themselves from the inclemencies of the weather is the desire for artistic effects to be obtained in coloring the materials of which these protective coverings are made. From Greek mythology we learn that Ariadne, the goddess of spinning and weaving, was the daughter of Idon the dyer of wool, a truly interesting chronological comparison, and one showing how intimately the art of dyeing was connected with its sister arts.

Perhaps the earliest authentic records we have concerning the industrial life of the ancient nations are those obtained in the historical classics of the Chinese; in these we find mention of the dyeing of silk in various colors as far back as 2600 B.C. The dyestuffs employed were those obtained from various plants. Dyeing, together with its related industry, printing, appears to have been practiced at very early times by the various East Indian nations, long before their migrations led to the settlement of Asia Minor and Europe.* . Remnants of dyed fabrics of great antiquity have also been recovered from Egyptian tombs.

As to the coloring matters employed by the ancient peoples in dyeing nearly all were of vegetable or mineral origin, and many were more or less of merely local occurrence. The dyer went out into the forest and collected the plants which had been found to possess tinctorial properties, extracted the coloring matter by boiling these in water, and employed this liquid decoction as the dyebath - The use of mordants was also known, for the majority of the vegetable coloring matters required -1 ?? the previous application of a suitable mordant in order subsequently to develop and render permanent the color obtained in the dyebath. In fact, it was known that by using mordants of different metals different colors could be produced with the same dyestuff, and in Pliny we find a description of how the Egyptians obtained variegated colors on a fabric by dyeing it in one. operation with a single dyestuff, having previously applied metallic compounds in such manner as to obtain the desired effect.

Indigo was known in very early times and was extensively employed, especially in Asiatic countries, for the production of blue colors. [A garment dyed with Indigo has been found in Thebes dating from 3500 B.C., and archeological researches have shown that the Egyptians dyed iron buff and used the yellow coloring matter of the safflower in dyeing as early as 2500 B.C.] Red was obtained from various vegetable extracts and also from the kermes insect, which somewhat resembles cochineal Madder was also used. Safflower, Saffron, Weld, Persian Berries, and other vegetable products were employed for dyeing scarlet and yellow. At the opening of European history the Phoenicians appear to have been most renowned for their skill in dyeing, and their beautifully colored fabrics became articles of extensive trade with other nations. The celebrated " Tyrian purple " appears to have had its origin among the Phoenicians, and its beauty and high price made it a badge of royalty. [Safflower was used by the Egyptians to dye silk a brilliant but rather fugitive scarlet. The Greeks in early times used it as a royal color and even in ancient Ireland (in fact up to the seventeenth century) the king's mantle was dyed with it. ]

This material was known to the ancients as "kermes berries" and was thought to be a vegetable product, and it was not until the eighteenth century that it was recognized as an insect similar to cochineal. Kermes was known to the Egyptians before the days of Moses, and was said to have been discovered by the Phoenicians. By the Hebrews it was called Tola, and by the Egyptians worm dye. In Persia its color was more sought after even than the Tyrian purple. [The scarlet color of the Tabernacle curtains of the Bible was no doubt produced with Kermes.] [A very complete description is given by Pliny in various parts of his "History of Nature" concerning the nature of the Tyrian purple and the methods employed for obtaining it from the shellfish, as well as the means of applying the color to fabrics.]

This coloring matter was obtained from certain shell-fish which were collected along the coast, and recent research has shown that this dyestuff was dibromindigo, a coloring matter which has now been prepared synthetically, as one of the modern " vat " dyestuffs. [See Friedlinder, Berichte der deutschen Chem. Gesellschaft, 1909, p. 765. The dyestuff was obtained directly from the shell-fish, 12,000 being used in the research, with a total yield of 1.4 grams of pure color.] According to Pliny, the Greeks, at the time of Alexander the Great, were acquainted with the art of dyeing wool in purple and other colors, and also of dyeing linen in black, yellow, blue, and green colors which were fast to washing. Plutarch tells us that in Rome dyeing was carried on as a handicraft, which Numa Pompilius endeavored to encourage and foster by establishing a college in the interest of this art. This "collegium tinctorum " is interesting to us as being probably the first school of dyeing ever established.

fig. 6 - Skein Dyer. (Middle Ages)

The Romans were acquainted with a number of different coloring matters, and divided them into major dyes and minor dyes; the first were used for dyeing garments for both sexes, whereas the second were employed solely for either men or women as the case might be. Yellow,. for instance, was only used for dyeing bridal garments. This was truly a remarkable sociological classification of dyestuffs. Pliny gives us a description of the following materials used in dyeing by the people of his time. He describes alum, and classifies it into white and black varieties; from his description, however, this term must be taken to include riot only the ordinary alum which we recognize, but also soda, which occurred in natural deposits in various localities, and probably several other such salts. We understand from Pliny, however, that the Romans were acquainted with the art of applying metallic mordants to wool; they appeared to have employed a decoction of sea-grass for fixing the alum mordant, much after the manner that cow dung was employed by dyers up to even rather recent times. The Romans were also acquainted with the use of tannin as a mordant in dyeing black, using a decoction of oak bark for this purpose. Among the various dyewoods mentioned by Pliny are genista (probably corresponding to our Flavine) for yellow, elderberry and walnut shells for brown, Woad for blue. The latter was applied in a vat somewhat like Indigo; the dye indicum is also mentioned, but whether this was identical with true Indigo or not is a disputed point.

Red colors were obtained from madder root; from the root of the red cabbage - the latter, in fact, is employed in Russia even to the present time, and is known in trade under the name of alkanna; while Kermes was used for dyeing a purplish red. Purple was dyed after the manner of the Tyrian purple, from the coloring matter extracted from a certain shell-fish.

fig. 7 - Cloth Dyer (Middle Ages)

The Venetians appear to have been the first of the more modern European nations [Benjamin of Tudelo informs us that a number of dyehouses existed in and around Jerusalem during the twelfth century, and that dyeing was entirely in the hands of the Jews.] to acquire skill in the art of dyeing, or in fact of any of the textile branches. [We find a reference in the historical records of Venice in 1194 concerning the importation of Indigo and Brazil-wood from India. This latter named dyestuff subsequently gave its name to the well-known South American country. Although Indigo was employed in Venice at this time, it does not seem to have extended over the rest of Europe when the subsequent decadence of Venice and its industries led to the widespread dissemination of the art of dyeing over entire Europe. This was probably due to a cessation more or less of the trade with India, which was not regained until the sea route to Asia was discovered.] From Venice the art of dyeing was gradually developed throughout the other European countries and soon reached a high stage of excellence in Holland, France, England, and Germany. Though Indigo was not generally introduced into Europe until the fourteenth century, Woad, a somewhat similar dyestuff, was used in its place, and when Indigo was imported in large quantities through trade with India, it had to overcome serious obstacles in its competition with Woad for dyeing blue. There appears to have been a kind of Woad syndicate in existence at that time with sufficient political influence to obtain severe laws against the use of Indigo in many of the principal countries, and this dye had to overcome tremendous opposition before it finally replaced the much inferior Woad.

[We find a reference in the historical records of Venice in 1194 concerning the importation of Indigo and Brazil-wood from India. This latter named dyestuff subsequently gave its name to the well- known South American country. Although Indigo was employed in Venice at this time, it does not seem to have extended over the rest of Europe when the subsequent decadence of Venice and its industries led to the widespread dissemination of the art of dyeing over entire Europe. This was probably due to a cessation more or less of the trade with India, which was not regained until the sea route to Asia was discovered laws against the use of Indigo in many of the principal countries, and this dye had. to overcome tremendous opposition before it finally replaced the much inferior Woad.]

[ A law of the Diet of 1577 prohibited the use of Indigo in Germany, it, being described as a "pernicious and corrosive dye." The first mention of Indigo in England is in the year 1581, in connection with black dyeing, but it does not seem to have been, used for dyeing blues. In a document of 1243 reference is made to the duties payable on Woad, and in 1268 an agreement was recorded between the citizens of Norwich and the woad merchants of Amiens, France. Coventry was famous for its blue-dyed woolen cloths as early as 1415, the color being known as "Coventry true blue." The first guild of dyers is mentioned in 1188, but the first charter of incorporation was granted to the Worshipful Company of Dyers in 1471.]

The discovery of America gave a great impetus to the art of dyeing, by making a large number of new coloring matters available for use. Logwood, and the various red woods of Central and South America were introduced, and were soon extensively employed. [Even Logwood appears to have aroused considerable opposition when first employed, as we find an edict of Queen Elizabeth prohibiting the use of Logwood, and directing that all of this material found should be burnt. James I, in 1620, prohibited the import of Logwood, but dyers apparently employed it under other names.]

Fustic was also an American product, and so was cochineal. All of these new materials were exceedingly valuable additions to the dyestuffs employed at that time, and soon came into extensive use. The Netherlands and became the great centers of wool dyeing, a position which they maintained for a long period of time, but the art gradually perfected itself in England and Germany, as well as in France. The variety of vegetable coloring matters which were employed was very numerous, and some were rather peculiar and interesting. In England, for instance, a yellow coloring matter was extracted from onion skins, and was quite extensively employed.

Up to the middle of the last century dyeing had a rather gradual and even development, though but little attempt was made towards a scientific study of the subject; but the year 1856 brings us to a period of revolutionary development. It was in this year that [William Henry] Perkin, an English student working under Hofmann in Germany, discovered (during a research which had for its object the synthesis of quinine) that the oxidation of aniline yielded a beautiful violet coloring matter of great tinctorial power. This was the beginning of the era of artificial dyestuffs prepared from the various products of coal-tar, and proved to be an important landmark in the industrial, development of chemistry. Not only did this discovery soon bring about a complete revolution in the methods of dyeing through the preparation of numerous artificial dyestuffs, but it also brought the art of dyeing into a more intimate and direct connection with the science of chemistry, which was then growing with rapidity.

Previous to that time the methods of dyeing were eminently unscientific, crude, and more or less surrounded with mystery and supposed secrecy of skill. The chemist had been too intently occupied in other fields to become interested in the working out of the scientific principles of dyeing, and only a very few scientists had engaged themselves in its investigation. But the discovery of the coal-tar colors opened up a wide arid most lucrative field for chemical research, and this soon led to a close association of dyeing and chemistry to the mutual benefit of both subjects. From the dyestuffs themselves, the chemist was led to an investigation of the processes and methods of dyeing, and a chemical study of the fibers and mordants, and the action of the various drugs employed. The result was that order and system and knowledge of underlying principles in dyeing were soon introduced, where before everything had been more or less obscure and chaotic and dependent upon rule of thumb methods. From that time on, dyeing became incorporated in the general science of chemistry, and has since drawn its sustenance from and reached its highest development under the guidance of that comprehensive parent of so many industries. The old, crude methods of dyeing have been relegated more or less to the mysteries of antiquity, and have given way to concise, clearly understood ' and scientific processes. The majority of vegetable coloring matters, whose use necessitated usually cumbersome and lengthy methods of application, have been replaced almost exclusively by the various coal-tar colors, which are easily and quickly applied.

The colors obtainable with the old dyes were also subject to many limitations; brilliancy of hue in many instances was impossible, and the range of shades ordinarily obtained was rather narrow, and not capable of much extension without seriously complicating the dyeing process. The introduction of the coal-tar dyes made it possible to obtain colors which had hitherto been the despair of the dyer; and the latter has now at his command the most varied shades, and the most delicate and brilliant hues. But very few of the natural dyes have left even a vestige of their former selves in trade; some still retain their prestige on account of their good qualities and cheapness. Indigo has heretofore been the principal dyestuff of trade, and was a natural vegetable product which withstood all the competition of artificial substitutes; but the last few decades have seen the successful synthesis of this very dyestuff from coal-tar products, and it will only be a question of time before the vegetable dye will be driven entirely from the market. A similar result was witnessed in the case of Madder, which formerly ranked almost equal to Indigo in commercial importance; it was prepared by chemical means from coal-tar under the name of Alizarine, and soon displaced the natural dyestuff entirely.

Logwood still retains its importance among dyestuffs, principally on account of the good, cheap blacks which can be obtained with it. It is surpassed, however, in fastness by several of the coal-tar blacks, and for many purposes has been replaced by these colors. Cochineal is still used to some extent for the dyeing of scarlets and reds, but its use is fast decreasing, giving way to the various coal-tar red dyes, many of which surpass it in fastness. Fustic is employed somewhat at the present time, but chiefly in combination with Logwood for the production of blacks. It is rarely used as a self-color for dyeing yellow, for many of the coal-tar colors surpass it in purity and brilliancy of hue, as well as in permanence of color.

3. Dyes of Antiquity Compared with Modem Dyes. At this point it is of interest to discuss briefly the comparative permanence and color values of the old natural dyes and the more recent coal-tar dyes;

Many other vegetable dyes were used for the production of colors, but these were known as "false" colors and were not fast for much is said (especially by those more or less unacquainted with the properties of dyestuffs) of a derogatory nature concerning the modern colors, while the fastness of the old dyes is highly extolled. [In the eighteenth century the practice of dyeing was regulated by very strict rules under the "Regulations" of Colbert, and a dyer was not allowed to dye "true" colors with any of the "false" dyes. This close government regulation had the beneficial effect of bringing into use the best and fastest colors available, as the dyer was not allowed to misrepresent his goods.] If we examine in review the former vegetable dyes we will find that perhaps the fastest one of all is Indigo (used for obtaining blue shades and for mixed shades containing blue); as this identical dyestuff is now prepared from coaltar, we need not proceed further with the comparison in regard to it. There are also other blue dyestuffs of artificial origin which are eminently fast and more easily applied than Indigo (Alizarine Blues, etc.), and though recently introduced, vat colors are even much faster than Indigo. Red was formerly dyed almost exclusively (where fast colors were in question) with Madder on previously mordanted wool; as the coloring principle of Madder is made at the present time from a derivative of coal-tar, and is identical in every respect with that occurring naturally in the vegetable dyestuff, we have at our command the same conditions of fastness as the people of antiquity; we have also far extended our range of fast colors in this respect by the preparation of blue, yellow, brown, green, and black dyestuffs belonging to the same class as Alizarine Red (Madder) and possessing similar dyeing qualities. Weld and Persian Berries appear to have been the fastest yellow dyes possessed by the ancient dyers, and these do not compare to our Alizarine Yellow (and some other coal-tar yellows) in respect to fastness and clearness of shade. The other yellow dyewoods which were extensively used were all rather fugitive, which accounts for the fact that most of the solid yellows in the old fabrics are found to be much faded, and also the compound shades of which yellow was a component exhibit a faded appearance. Dull russet yellow and orange shades were sometimes obtained by the use of a metallic pigment, and these, of course, being mineral bodies, were extremely fast, but they lacked brilliancy and clearness of tone. This color was obtained by steeping the material to be dyed in iron liquor, prepared by dissolving iron filings in vinegar (acetate of iron), and then drying in the sun. Green colors were obtained by the use of the mineral pigment verdigris; there do not appear to be any green vegetable dyes of importance, though it is said the Chinese were acquainted with a green dyewood called Lo-kao which possessed great beauty and fastness. It was probably derived from the leaves of certain species of Rhamnus; it was, however, exclusively employed in China and was unknown outside of that country. Green colors in modem methods of dyeing, where fastness is desired, are obtained by compounding fast yellow and blue dyestuffs to the desired shade of green. Black was formerly dyed by two methods. The first employed Logwood or a similar dyewood capable of yielding a black color on mordanted wool, in which case the black was not extremely fast, especially to light and exposure; we still employ Logwood for dyeing cheap blacks on wool, but we have many other coal-tar colors which possess superior fastness. In the second case, black was dyed by forming a heavy deposit of tannate of iron in the fiber. A decoction of iron filings and oak bark was made with water and this was spread over the cloth to be dyed, which was then rolled up and allowed to remain for about a month; by that time the iron rust had permeated the cloth, and it was then dyed black by steeping in a decoction of gallnuts. This was a rather crude and lengthy process, to say the least, and not at all adapted for modern times. Brown shades were usually obtained by steeping the cloth in a decoction of walnut husks and lime water. [A valuable source of information concerning the dyeing processes of antiquity is a book published in Venice in 1548 by Plichto. This person was an officer in the Venetian army and his real name was Giovanni Ventura Rossetti. It was one of the first books of its kind ever published, and contains numerous recipes and processes for dyeing which the author had personally collected in his extensive travels through Europe and the Levant. A German book on dyeing had already appeared at Strassburg in 1514, and contained a description of various dyeing processes used in Germany at that time. From the descriptions given in this book it appears that a mordant of alum was the basis of nearly all the colors dyed in Germany. The first book dealing with the subject of dyeing printed in English appeared in London in 1583, and was a translation.]

At the present time the great demand placed on the dyer is cheapness and volume of production, which must often be attained at a considerable sacrifice of fastness of color. If time and expense were not so carefully economized, there is no reason why the modern dyer (if he be well acquainted with the principles of his profession) should not turn out colors of equal fastness, if not superior in many cases, to the colors of antiquity, and the range of shades at his command would be far more extensive. We must bear in mind that the old dyeing processes were usually long and tedious methods, and time was little or no factor in the operation. If greater brilliancy of hue is desired, as is frequently the case in modern tunes, it is obtainable only by the use of certain colors, the majority of which are not characterized by any special degree of fastness. These modern dyes far surpass the old ones in this quality of brilliancy and purity of tone, but if such quality is demanded, a high degree of fastness must at the same time be sacrificed.

4. Apparatus and Equipment for Dye-Testing. In carrying out the dye-tests to be described in this book, it will be found convenient to employ skeins of wool and silk weighing 5 grams and if cotton 10 grams. The dyebaths should conveniently contain about 300 to 400 cc. of water, and should be of porcelain, glass, or enameled iron-ware. A good form of experimental dyebath is that shown in the illustration (Fig. 8). It consists of a round copper or sheet-iron vessel lined inside with asbestos, and provided with a perforated iron bottom and top. Its top contains four openings through which the dyepots are inserted. This airbath is placed oil an iron stand provided with a gas burner. The dyepots are porcelain and are held by beveled copper collars with wooden handles. The airbath is so arranged that when the dyepots are in position they are raised about an inch above the bottom plate. Such a dyebath allows of a uniform heating of the four pots, and the temperature may be raised rapidly or slowly at will, by regulation of the gas flames, and it is an easy matter to bring the liquid in the pots to an active boil.

Instead of using a gas burner to supply the heat, it will be found convenient, where electricity is available, to employ a round electric stove plate, in which case the body of the using a may be placed directly on the electric stove, and the perforated bottom may be dispensed with. This method of heating gives a very uniform temperature in all four dyepots, and as the heat is easily regulated it may be maintained at a constant point, and so avoid overheating of the dyepots.

There are other forms of experimental dyebaths in use where solutions of calcium chloride, common salt, glycerin, etc., are used for heating the dyepots. Strong solutions of calcium chloride are capable of being heated far above the boiling-point of water, and consequently in such a bath it is easy to bring the dyepots to the boil. But calcium chloride solutions attack the baths in which they are contained. In case of copper vessels with soldered seams the solder is rapidly eaten out and leaks frequently occur. In a dye-bath using a solution of calcium chloride the seams should be brazed, which makes the apparatus rather expensive, and even then the copper itself is soon attacked.

In large dye laboratories to be met with in dyestuff factories or dyehouses and mills, and where a dyebath is required to take care of a large number of dyepots at once, a good form of apparatus is a cast-iron or wooden trough 1 to 1.5 ft. wide, 3 to 4 ft. long and about 10 ins. deep. This is lined with a good quality of sheet lead. The top consists of sheet lead properly braced, and containing openings for the dyepots. In this form of bath several dozen pots may be heated at once. The solution used in the bath should be calcium chloride of such strength that a temperature of 220' F. may be obtained.

This will be sufficient to allow of the dyebaths in the pots to be brought to the boil. The heating of the bath is effected by a lead steam coil. With solutions of common salt -it is difficult to obtain a temperature of 212' F. in the dyepots; that is, to bring them to a state of active boiling. A temperature of 210' F., however, can be maintained, and probably this is nearer the actual temperature of the open dyevat in practice, and gives as good results as if the liquid was in an actual state of ebullition. Solutions of common salt are perhaps to be preferred to those of calcium chloride where a copper dyebath is used, as they do not have a corroding action. By the use of glycerin in the bath a boiling temperature can readily be obtained in the dyepots, but glycerin baths continually emit disagreeable vapors. Whenever possible, baths containing such solutions should be heated by a steam-coil (with steam under pressure) rather than by direct gas flames. The great disadvantage of all baths using solutions, and one from which the airbath is free, is that the water is constantly being evaporated from the solution and has to be as constantly replaced.

When dyeing the test skeins they should be systematically " worked or turned in the dye solution. This is best accomplished by suspending the skein in the bath from two glass rods, and using these from time to time for the purpose of turning the skeins. These glass rods should be ?? I to 1. in. in diameter, and 8 to 10 ins. in length. The skeins should be turned sufficiently to insure even penetration of the solution through the entire portion of the material.

fig. 10 - Yarn Reel

The dye solution employed in the baths will usually cause discolorations on the porcelain or glass beakers used, as well as on the glass rods and other vessels with which they come in contact. In starting a new dye-test it is essential that all of the apparatus be clean and free from previous dye stains. As many of these stains cannot be removed readily by water or soap solutions, stronger chemical treatment is generally necessary. For this purpose, it is well to have on hand a strong solution of chromic and sulphuric acid. This is prepared by using about 1 part of solid sodium bichromate with 10 parts of strong sulphuric acid (sp. gr. 1.84). This mixture, should be kept in a stout glass or porcelain container. It will remove almost all color stains on apparatus and can be used over and over again if care is taken not to dilute it unduly. As the solution is very corrosive it should not get on the hands or clothing or on metal ware.

The skeins of yarn for use in the test experiments may conveniently be made on a small yarn reel, such as is used in most yarn mills for making test skeins to determine the size of the yarn (see Fig. 10). In the case of wool and silk yarns the material will generally be obtained in the form of large hanks or skeins. These will have to be put on a suitably sized 'swift" (or frame for holding the skein) and run therefrom to the reeling machine. In the case of cotton, this can usually be obtained in the form of cones, which are far more convenient to reel from. There is wide variation possible in the selection of the yarn to be used.

fig. 11 - Porcelain Dyepots

It is well not to use too fine a yarn, as this consumes considerable time in the preparation of the test skeins; also finer yarns are more expensive than coarser ones, and are more liable to break and tangle up. In the case of wool dyeing, two-ply, soft worsted yarns will yield better looking tests than carded woolen yarns. With silk it is best to have twisted thread silk yarns, as these will break and tangle less and may be easily rewound if required. If this form of silk yarn is too expensive, however, spun silk yarn may be used. With cotton it is well to use a good quality two-ply combed peeler yarn (in size about 2/20's or 2/16's).

As already mentioned, the wool and silk should be made up into skeins weighing 5 grams, while the cotton is used in skeins of 10 grams. The dyestuffs and various chemicals employed in carrying out the dye-tests should be used. in the form of solutions of such strength that small quantities of the products may be measured out in convenient volumes. As the amount of material being dyed (5 or 10 grams) is relatively small, and as small amounts of the dyestuffs, etc., are used, it would be both inconvenient and inaccurate (unless very precise weighings were made on expensive and accurate balances) to weigh the chemicals employed in each test; but by preparing solutions of definite strengths the required amounts may be readily and accurately measured off. The proper preparation of these solutions will be taken up as demanded by the course of the experiments. For the measurement of the solutions a glass cylinder graduated into100 cc. is very convenient; this readily permits of the rather accurate measurement of such quantities as 5 cc., 10 cc., etc. Volumetric measuring flasks of 100, 500, and 1000 cc. capacity are also convenient for the preparation of standard solutions of dyestuffs and chemicals. In cases where very minute quantities are desired, and it is necessary to measure to an accuracy of 1/10 cc., a small glass tube (known as Mohr's pipette) accurately graduated to 1/10 cc. is very useful.

These pipettes may be obtained in sizes holding 5, 10, 25, or 50 cc., and by their use volumes accurate to 1/10 cc. may be readily measured out. A thermometer is also necessary for use in the dye-tests. A good, practical and inexpensive form is the so-called "dairy" thermometer with a paper scale and reading to 220 dg F. By the use of this thermometer the temperatures of the dye solutions or other liquids employed in the tests may be ascertained, An agate cup (pint or quart size) is a useful adjunct for the preparation and mixing of the various solutions needed. A bunch of small tags should also be available so that every skein with which a test has been made may be properly labeled for identification and reference.

5. Practical Process of Dyeing. - In carrying out the methods of dyeing on a practical scale, the object is usually to impregnate the material to be dyed with the various solutions of coloring matter or other materials which may be employed. There are two general methods of procedure for this purpose:

(1) The textile material is simply immersed in the dye liquor, and moved about or "worked" in such a

manner as to promote an even distribution of the color. The form of the material being dyed will, of course, necessitate modifications in the method of handling. In the case of loose wool or cotton, the material is immersed in a suitable vat or tank containing the dye liquor, and is stirred about from time to time by means of poles. When yarn is to be dyed, the skeins are placed on sticks and hung in the dye liquor contained in a tank of suitable dimensions and usually of rectangular form, the sides of the tank supporting the dye sticks. The position of the hanging skeins is changed from time to time by turning so that every part will be equally exposed to the action of the dye liquor. In the case of cloth (or woven fabrics in general), the ends are joined together, thus forming an endless string which is run continuously through the dye liquor over a rotating "winch." Of course various mechanical devices have been introduced for the purpose of economizing labor and for automatically moving the material with a minimum amount of injury to the fiber. Although a considerable quantity of loose wool and cotton is still dyed in the primitive fashion by hand poling, the more approved method is to employ machines for stock-dyeing. These usually consist of a large basket divided into several interior compartments. The stock is loaded into the basket which is then made to rotate in the dye liquor contained in an outer tank into which the basket fits. Yarn may be dyed by placing it on sticks held in a revolving frame which moves slowly through the dye liquor. Cloth may be automatically run through the dye liquor in string form by means of moving rollers, or it may be moved back and forth in open width by passing from one roll to another (as in the jigger).

fig. 17 - Hand Vat for Dyeing Loose Stock.
(both Direct and Indirect Steam)

Fig. 18 - Round Wooden Dyevat, Vertical Section

(2) The material to be dyed may be held stationary in a compact form and the dye liquor is circulated through it by means of pumps or steam or air pressure. Machines of this type are coming into vogue very largely at the present time, as they possess the advantage of being able to handle large quantities of material in a small space, and furthermore they do not injure the goods by the mechanical straining and friction necessitated in the older methods. Large economies in dyestuff, steam, and water are also possible.

fig 19 - Series of Vats for Dyeing Loose Stock

The construction and methods of operations of the various types of dyeing machines will be taken up in detail in their proper connection. The practical operation of dyeing usually necessitates several consecutive processes, as follows:

(1) Scouring (or wetting-out)
(2) Dyeing (which may also include a mordanting operation)
(3) Rinsing
(4) Hydro-extraction (or removal of the excess of water by squeezing centrifugal action, or wringing)
(5) Drying

The exact nature of these processes and the appliances employed in carrying them out will depend very largely on the character and form of the material being dyed.

fig. 20 - Showing General Principle of Pack System of Dyeing

fig. 21 - The Drexe Dyeing Machine. (Showing Pack System)

6. Water and Steam in the Dyehouse.-

As water is used in relatively large quantities in nearly all the operations of dyeing, it becomes an essential feature to be considered carefully in the practical dyehouse. It is not only necessary that water be available in large quantities and at a low cost, but also that it be comparatively pure in quality, of a low degree of hardness, and contain a minimum amount of iron. Owing to the importance of the water in dyeing, it will receive a special consideration in the course of this work.

The amount of water required in dyeing operations depends both on the nature and character of the fiber as well as the construction and form of the machine in which the dyeing takes place. When the material is dyed in the open-that is to say, not packed tightly in the machine, but where the goods are required to be worked in the solution there will be required a sufficient volume of water to properly manipulate the goods. Cotton takes less water than wool or silk, being a more compact fiber and yielding denser yarns and woven goods. It requires about twenty times its weight of water for the dyebath; that is to say, 1 lb. of cotton yarn, for example, will require about 2-1/2 gallons of dye liquor in which to dye it, and a vat for dyeing 100 lbs, of Cotton is usually figured so as to contain 225 to 250 gallons of liquor. Wool and silk will require about twice the proportion of dyebath as cotton; that is to say, 1: 40 or 1: 50, or 1 lb. of wool (or silk) in skein yarn form will require about 5 gallons of dye liquor; less than this will be found impracticable, as it will not be possible to work the material satisfactorily in order to obtain uniform penetration. Where dyeing machines are used of such a character

that only a portion of the material is in the dye liquor at any one time, or where the material is tightly packed and the (lye liquor is circulated through it, a much smaller proportion of liquor will be needed than that mentioned above. Under these conditions the relative proportions of water and fiber may drop down to as low as 1: 15 or even 1: 10.

For purposes of rinsing after dyeing it will require at least as much water as originally employed for dyeing, the purpose being to replace the residual dye liquors held in the interstices of the yarns and fibers with clear fresh water so as to wash away the color which would otherwise be superficially deposited on the goods. In general it may be stated that each pound of dyed yarn will require from 2 to 5 gallons of water for proper rinsing. Of course, there may be cases where a much more thorough rinsing is necessary, and in consequence, a greater proportion of water will be needed.

As most of the liquors employed in dyeing, scouring, etc., are heated and often require. to be raised to the temperature of boiling, it is manifest that large quantities of steam are used in the dyehouse. In the old days, dyevats were heated by direct fire, but at, the present time steam heating is universally employed. Heating by steam may be done either by the use of a closed coil of pipe, or by the use of a perforated pipe, and thus blowing the live steam directly into the liquor. fie former method is preferable, as it does not introduce into the dyebath any of the impurities (such as oil) which may be carried along by the steam. Also the dyebath does not become continually diluted by water from the condensed steam. Another bad feature of having live steam blowing directly into the bath is that it causes excessive agitation in the liquor which may result in the tangling and felting of the goods, and also the goods directly in contact with the live steam are in danger of becoming overheated and injury to the color or to the fiber itself may result.

fig. 25 - Cop Dyeing Machine

Economy in the use of steam has an important bearing on the actual cost of dyeing. As steam for the dyehouse is usually obtained in connection with steam for the power plant, it is often possible to employ the exhaust steam from the engine for the purpose of heating the dyevats. This, however, is not possible where a condenser type of engine is used, though arrangement may be made whereby the hot water from the condenser may be utilized. Steam for heating dyevats should not be employed at a very high pressure (such as employed for engines), but a reducing valve should be introduced into the steam-main coming into the dyehouse so that the pressure may not be over 40 lbs.

The problem of removing the dense vapors usually encountered in a dyehouse is an important one, both on account of the health of the operatives, and for the production of good work. These vapors may be removed either by the use of a suction fan or by the natural ventilation obtained by a suitable arrangement of the dyehouse roof. In cold weather satisfactory results in the removal of fog cannot be obtained unless heated air be introduced into the dyehouse in case suction fans are employed, for as the fan expels the air from the dyehouse, if fresh cold air is drawn in from the outside it will help to increase the fog by lowering the temperature inside.

A good plan is to draw the entering air from the heated drying rooms or the boiler house, and this will be found to expel rapidly any fog produced in cold weather. In case the dyehouse is located in a separate building of a single-story construction, it is possible to arrange the roof in such a manner as to give excellent ventilation which will effectually remove all fog in both warm and cold weather.

As proper light has an important bearing on the problems of color matching, a dyehouse well lighted from a northern exposure would be the most suitable. This, however, cannot always be practically realized; although under the conditions prevailing the best light possible should be given the dyehouse, and the usual practice of placing this department of the mill in a dark basement should be condemned.

7. Forms in Which Textiles are Dyed.-With respect to the form in which textile materials are dyed, this varies greatly with the circumstances of manufacture. Wool is extensively dyed in the loose state, and also in the form of slubbing and tops. Yarns of both wool and worsted are also largely dyed. In cases where woven fabrics are to be finished in solid colors, the dyeing is generally done in the piece. Cotton is also largely dyed in the loose state, though both yarns and piece-goods are extensively colored. Silk is dyed chiefly in the form of skeins of yarn, and to a much less degree in the piece. Loose silk, of course, can only be dyed in the case of waste silk. In the case of both cotton and wool, it is cheaper to dye in the loose state than in the form of yarn, and there is but little trouble experienced in getting the resultant yarn even in color, as the carding, drawing, and spinning processes will even up any irregularities which may have been formed in the dyed color of the loose stock. The color also has better penetration and in some cases is faster. There is also a considerable saving in the manufacturing costs, for when yarn is dyed it is necessary to reel the yarn from the cops or bobbins (on which it is spun) into the form of skeins; these latter are then dyed, and must again be wound back into the desired package, such as bobbin (for weaving), cone, or tube. Whereas, if the material is dyed in the loose stock, the cop or bobbin obtained by spinning is used directly for weaving, or is wound directly into tube or cheese, if desired for other purposes.

There are some drawbacks, however, to dyeing in the loose state. In the first place, there is always more or less of the colored material left over in the manufacturing in the form of card waste, slubbing, roving, etc., which has a lower value, as it is much harder to utilize than if the fiber were undyed. In the second place, the dyed stock is generally somewhat more difficult to manufacture and spin than the undyed, the fibers becoming more or less matted together, and lose considerable of their elasticity and good spinning qualities. In the case of cotton, most of the natural wax on the fiber is removed so that the stock is difficult to card and spin. On this account it is not always feasible to dye cotton in the stock, as the fiber may be left in a condition impracticable for spinning. Furthermore, stock dyeings, as rule, do not have the brilliancy or purity of hue, which is obtainable in skein dyeing, for the manufacturing processes through which the stock must pass deteriorate, more or less, the quality of the color.

Dyeing in the piece is of course the cheapest form of handling textile materials, as in this case there is no after-waste of dyed material; but, of course, piece dyeing is limited to the production of solid colors-that is, a single color over the entire piece. There are, however, certain methods by which two color effects may be obtained, such as using mixed fibers (wool and cotton, silk -and cotton, etc.) or by employing yarns especially treated so as to take a deeper color or not to take the color at all (resist yarns).

8. Hydro-extracting and Drying.-The purpose of hydro-extracting (or squeezing) is to remove the large amount of water which is mechanically held in the interstices of the fibers so as to permit of better and more rapid drying. Yarns, cloth, etc., even after thorough squeezing will still retain from 1 to 11 times their weight of. water. By hydro-extracting in an efficient form of centrifugal machine the proportion of water left in the goods is about 65 to 100 per cent of their weight; that is to say, 100 lbs. of dyed and rinsed yarn, for instance, after being properly centrifuged will still contain about 65 to 100 lbs. of water.

The drying of dyed material is a process, ofss ?? which has to be carried out carefully, and in many cases with proper respect to the dyestuff employed.

fig. 36 - Stretching and Glazing Machine for Yarns

The apparent color of the material at times alters considerably on drying; this is especially true of cotton, which always appears much darker in color when wet. Nearly always some form of artificial drying is resorted to, as drying in the air is generally inconvenient and also takes too long.

Generally suitably heated rooms are used, or machines specially constructed to take care, of the material being dried. It is never well to dry at a very high temperature, as this will usually affect both the fiber and the coloring matter, though there is not much chance of danger if the temperature is kept at 180' F. or lower.

9. After-treatment of Dyed Material.-It is frequently necessary after dyeing to subject the dyed goods to further operations which may properly be considered as merely a continuation or finishing off of the dyeing process. Woolen material, for example, is sometimes soaped in order to remove excess of coloring matter. Cotton dyeings are frequently passed through a softening bath containing usually an oil emulsified with soap or alkali. A small amount of oil is thus left in the fiber which has the effect of softening the goods as well as of brightening the color.

fig. 31 - Silk Skein Stretching and Lustering Machine

Many operations of dyeing tend to make cotton harsh and stiff, as when mordanting with tannin and metallic salts or with sulphur dyes. The oil treatment much improves the appearance and handle of the dyed goods. Silk is very often "brightened" and "scrooped" after dyeing; this is usually accomplished by passing the dyed goods through a bath containing acetic or tartaric acid, squeezing, drying, or steaming and stretching in a special machine.

The effect of the acid is to give the fiber a crackling or crunching sound when squeezed in the hand, which is the so-called " scroop "; while the steaming and stretching serves to straighten out the fiber and give it a high luster. In old methods of dyeing woolen goods the dyed color was frequently it saddened " by passing the goods through a bath containing copperas (sulphate of iron). The effect of this was to form an iron lake with the dyestuff (usually a vegetable mordant coloring matter), which was always darker and duller than the other lakes, and thus dulled or " saddened the color.

[ More excerpts from Matthews Book are coming. Next one will be Vat Dyes & Indigo.]

Back to top page of J.M. Matthews book

Application of Dyestuffs
To Textiles, Paper, Leather and Other Materials

INTRODUCTION

Back to top page of J.M. Matthews book

Application of Dyestuffs To Textiles, Paper, Leather and Other Materials

INTRODUCTION

Application of Dyestuffs
To Textiles, Paper, Leather and Other Materials