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COLORS FOR TEXTILES
Antienf
...
and
. . . MODERN
Left: Dyeing establishment in 1568 Above: Equipment used in manufaduring colors includes vatq filter presses, dryers, and ball mills. A vat and filter press are shown.
MAX BENDER Interchemical Corporation, New York City Dyestuffs, pigments, and auxiliary-application compounds used in textile decorating through the ages are described.
THE
art of applying color to textile fabrics goes far hack into antiquity. The unearthing of colored fabrics in the course of excavations in Egypt, Asia, and the Americas has proved beyond question that textile coloring was developed independently and practiced by almost all primitive peoples. The earliest dyes probably were made by men who observed the stains left by various parts of many plants. They learned that a great number of these dyes could be fixed on fabrics only by the use of auxiliary materials, such as acids and metallic salts, and that there was often much improvement in color and brightness due to such treatments; this was the beginning of the important practice of mordanting. Mineral dyes came into use when men discovered the art of staining fiber or fabric in springs containing iron salts. Springs of this kind occurred in many vicinities, and it was a simple matter to obtain interesting shades
of orange and red-brown by soaking yarn or fabric for various lengths of time and then drying it in air. In addition, colored mineral earths (pigments) were applied by mbbing them into textile materials. The various primitive groups thus discovered in their own localities different sources of coloring matter. However, as tribes migrated and contact with other groups was established, men learned of dyestuffs which were faster or more briUiant than any to be found in their own vicinity, and trade in dyestuffs began. Of the hundreds of known dyes used at different times and in different regions, the majority were discarded as trade became general. Only 25 to 50 were still employed in medieval times. Of these, the most noteworthy were indigo, woad, logwood, madder, Tyrian purple, kermes, cochineal, fustic, and cutch. In recent years the art of textile decorating has improved markedly owing to the introduction of a host of 2
JANUARY. 1941
newly developed dyes and pigment colors, and auxiliary chemicals to facilitate their application. All the natural dyes except a mere handful, including logwood, fustic, and cutch, have been replaced. Modern colors are relatively inexpensive, brilliant in shade, and of a wide range of hues; they are applicable to the valious present-day fabrics and are fast to light and washing (2, 10,19).
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manufacturers prevailed upon their governments to restrict the importation of indigo when it did become readily available (10). LOGWOOD
Logwood is one of the few natural dyes still used on a large scale in modem dyeing practice. Depending upon the auxiliary chemicals used in its application, logwood can be employed for dyeing purple on wool, blue and INDIGO black on cotton and wool, and purple and black on silk. Indigo blue is one of the earliest, most important, and I t was introduced from Mexico into Spain in the 16th popular dyestuffs known to man. Until economical century, where i t became popular and effected great methods for its synthesis were discovered in the 19th expansion in the art of dyeing. However, it did not century, it was obtained from the leaf of Indigofera meet with favor in England until 100 years later. Also known as campeche wood, logwood is extracted tinetoria, indigenous to many parts of Asia, Africa, the East Indies, the Philippines, and the Americas. Sam- from the wood of the tree, Haematoxylon campechianum, ples of cloth dyed with indigo have been found in Egyp- which grows in tropical and subtropical areasin America. tian tombs, Inca graves, and other widely separated Freshly cut wood from the tree is colorless; as with insites of excavation. India began to apply it to textiles digo, the color probably exists as a glncoside. The more than 4000 years ago, and also supplied it to Egypt wood, in the form of chips or paste, is fermented to preand the rest of the then-civilized world. Columbus pare the color for dye application (10). and other explorers reported that indigo was in use in MADDER the New World, and cultivation for export to their Madder probably was used first in India, but the mother country was started by early settlers. evidence from excavations indicates that it was also Themethod of preparingindigofrom the plant changed well known to the ancient Persians and Egyptians. Reflittle from ancient times. The leaves were steeped in water from nine to 14 hours; fermentation took erence to the use of madder was made by many Greek place, resulting in hydrolysis of the coloring material, and Roman .writers, including Pliny the Elder. The indican, originally present as a glucoside, to glucose and ancient Gauls also were familiar with it. There is no record of the production or use of madder the water-soluble leuco form of indigo. Then the ferment liquor, which varied in shade from yellow-orange in Europe during the period following the fall of Rome. to olive-green, was drawn off and aerated so that oxida- In the East, however, trade in this dye continued imtion took place and indigo blue precipitated out. The portant with Bagdad as a center. European interest top liquor was decanted and the sludge heated to stop in madder revived about 700 A.D., and cultivation was fermentation; more liquor was filtered out, and the .paste, after drying in blocks, was ready to ship (10,11). WOAD
Woad is a blue dye generally conside~edinferior to indigo. It was obtained from the leaves of a plant native to the temperate zone. The ancient Chinese and Egyptians are known to have cultivated it. Julius Caesar found the inhabitants of Britain using woad to paint their bodies. The Gauls were familiar with its use as a dyestuff. To prepare the color, the leaves of the plant were ground to a pulp which was kneaded into balls and spread out to dry for a prolonged period. Then the lot was pulverized, mixed with water, and subjected to controlled fermentation for approximately nine weeks to give aproduct ready for market. Woad enjoyed nearly 1200 years of supremacy in western Europe before it was replaced completely by indigo in the 18th century. Indigo had been imported by the Venetians for use in their dyeing arts as early as 1194, but several factors prevented i t from supplanting woad. Communications were slow, the all-water route to India was not discovered until 1498 (by Vasco da Gama), and powerful syndicates of woad growers and
Courbsy oi U e New York Botanical Garden
Wild Indigo. cu1ti.r.tion of Indigo Wa.ono. s n Important 1ndu.trY
begun throughout the civilized world. Spain and Portugal were for a time dyestuff centers because of their maritime ascendancy, and madder was one of the items which passed through their ports. Late in the 15th century Holland became very proficient in the growing of madder and maintained supremacy in its production and use for some 300 years.
JOURNAL OF CHEMICAL EDUCATION
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Other European countries, including France and England, cultivated madder, but i t was not until the 18th century that the French were able to compete successfully with the Dutch who had given much study to the cultivation and recovery of color from the madder plant. To promote the industry in their respective countries, France and England adopted such expedients as dyeing all military uniforms red with madder, hence the term "redcoat" for the British soldiers in the American Revolution. During the middle of the 19th century madder production reached a total of 70.000 tons a vear. It was grown in most of Europe, and in the Near East, North Africa, the Azores, the Americas, India, and Australia.
Courtesy of the New York Botanical Garden Wild Medd..
.
D..whg
from . n Old Book
Madder growing was abanaoned in most parts of the world after the synthesis of the color made i t available a t a price about one-quarter the cost of its extraction from the plant. The synthetic preparation of the anthraquinone compound alizarin, the color component of madder, was discovered in 1869 by Graebe and Liehermann. The coloring principle of madder comes from the roots of a number of herbaceous plants, generally Rubia tinctorum or Rubia peregrina. Most of the pigment is
found in a red mass between the outer skin and the woody part of the root; the pigment is composed of glucosides, the most important one of which is ruberythric acid. This glucoside is hydrolyzed to the dye alizarin when madder is fermented. In a typical extraction, the madder root was dried, treated with a mixture of potash and cow dung for three to four days, and then pounded in a mill to pulverize the heart of the root so that i t could be separated by sieving. The powder was stored for some time and fermentation developed the dyestuff (10, 13). TYRIAN PURPLE
During ancient and medieval times the possession of a garment dyed with Tyrian purple indicated royalty, power, or, a t the least, great wealth. Among the ancient Hebrews the color was used to denote sacredness. Tyrian purple possessed great brilliance and fastness in comparison with other known dyes. Large quantities of shellfish were required to make small amounts of this dye; demand coupled with laborious and costly manufacture made i t the most expensive color used in ancient times. Tyrian purple was obtained from purpura shellfish, a carnivorous species which occurs for the most part in warm seas. The dye is present in the mucous gland adjacent to the respiratory tract. When the yellowish mucus is applied to cloth and exposed to sunlight, the purple color develops. Tyrian purple was first made on the island of Crete as early as 1600 B.C. About 160 years later the Phoenicians began its manufacture in appreciable quantities for trading purposes. They searched for purpura shellfish along the shores of the Mediterranean and Adriatic Seas, and ventured into the Atlantic Ocean to reach the west coast of Africa where the fish were to be found in. large numbers. Dye works and trading posts were established at many points, the most famous of which was Tyre. The general method for extracting the color from purpura shellfish was to crush the mollusks, shell and all, or open them and remove the gland, then salt the mass for three days, and, finally, boil the whole in water for about ten days. The result was a clear concentrated solution of the dye. Flesh fragments and the insoluble foreign bodies were removed by skimming. The fabric was exposed to sunlight after steeping in the solution in order to develop the true brilliant color of Tyrian purple. The industry flourished long after the political eclipse of the Phoenicians. In the western Mediterranean i t declined onlv after the fall of Rome. The eastern Mediterranean industry shifted in 638 from Tyre as a center to Byzantium because of the conquest of Tyre by the Arabs. . There was a revival in Sicily during the Middle Ages in competition with the Near East, but the use of the dye in both the east and the west declined steadily due to the introduction of cheaper dyes, such as kermes,
JANUARY, 1941 and practically ceased after the Turks captured Constantimople in 1453. The chemical formula of Tyrian purple is related to the formula for indigo. It is the indigo molecule braminated a t the 6,6' positions. Synthesis of the dye is comparatively easy; however, the present demand for it is small, and other dyestuffs are used to achieve the color when necessary @,lo). KERMES
A brilliant scarlet color is obtainable from several species of the shield louse. One variety is kermes which lives on the leaves and stems of trees and shrubs with prickly leaves, such as the holly and the kermes oak. The kermes insect was found in most regions inhabited by ancient civilizations. Indications are that the Phoenicians, experienced dyers, were the first to recognize the color properties of kermes. The oldest evidence of the use of the dye is in the Bible. Rome prized i t so highly that she made it part of the tribute paid her annually by several conquered nations, including Spain. Hebrew and Arabian writers knew it to be of animal origin, but the Greeks and Romans supposed i t to be vegetable, an erroneous belief which persisted in Europe until the 17th century. When the Arabs spread westward after the Roman Empire fell, Europe became familiar with the techniques of kermes dyeing which the Arabs had practiced since ancient times. Venice was the principal trade center for kermes during the Middle Ages and the Renaissance, and she supplied the continent with scarlet cloth dyed in kermes imported from the Orient. Only kermes color was used to dye the fez and a cap of the same color worn by the Greeks. Kermes, grown in southwestern Europe, was exported from Marseille. Kermes was sold in the form of reddish brown pellets ahout the size of peas. Each pellet had a tiny hole and was filled with dark red particles which were the color substance. Pulverization of the pellets rendered the color easily soluble in alcohol or water. A pellet or ball consisted of a female kermes insect which had laid her eggs (the grains) and died, drying out to form a protective shield for the eggs. These balls were found stuck to branches. They were plucked and treated by vinegar bath or vinegar fumes to kill the eggs; after drying they were stored for eventual use. Late in the 17th century Mexican cochineal, another scarlet shield-louse dye superior to and cheaper than kermes, was introduced into Europe and kermes imports dropped markedly. With the advent of coal-tar dyestuffs,kermes disappeared almost entirely (4,lO).
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The conquering Spaniards recognized that cochineal was not only more available, hut superior to kermes, and began shipping the dyestuff to Europe, where i t eventually replaced kermes. It was one of the first dyes t o come from the New World. Numerous attempts were made to grow cochineal in other countries. These were successful in the Canary Islands, Spain, and parts of Central America. The cochineal trade was a t its height in 1870. Its decline heganwith theintroduction of the coal-tar dyestuff,aniline
,
Courtesy ofUle American Museum of Natural History, New York.
M u e x Shellfish YYlded Purple Dye
red, discovered by A. W. ~ o f & a n nin 1858. After azo. dyes superseded i t about 1880, use of cochineal became. limited to that of a nonpoisonous food colorant. The cochineal "grains," as marketed, are the dried. bodies of female insects. They are stable and show no. loss in dyeing potency even after many years in storage. Their shape is shield-lie, and they appear black, silver-. gray, or red. The insects live on the Indian fig tree or on nopal, a variety of cactus. They are prolific and can be har-vested as often as three times a year. (Only one or two. harvests a year are possible for kermes.) The fully grown female insects are brushed from the plants upon COCHINEAL which they feed into hags or small wooden bowls. They. Cochimeal is a scarlet dye obtained from the Coccus are then killed by the heat of an oven, by hot water, orcacti L. variety of the shield louge, which diiers in shape be steam. With this treatment they burst and turn from the kermes insect. Its habitat is Mexico. The bright red. The insects are dried andlose approximatelyAztecs cultivated it for its color, and, as the Romans one-third their weight. About 70,000 insects are re-. quired to make each pound of cochineal (4,10,17). with kennes, they exacted cochineal as tribute.
JOURNAL OF CHEMICAL EDUCATION OTHER NATURAL DYESTUFFS
Various other dyestuffs, chiefly of vegetable origin, were known to ancient man and later used by civilized peoples. Cutch is a brown dye extracted from acacia, cateohu, and mimosa wood. It has been used chiefly in Europe, America, and Asis, where the natives of India have employed it for over 2000 years. Yellow shades were obtained from safiron, weld, turmeric, old fustic, young fustic (also orange, brown, or dark olive shades), safflower (also orange and red shades), and quercitron (brownish yellow). Saffron, originally processed from pistils of a crocus plant (sativus) growing in Persia, was known to the Egyptians, Greeks, and Romans snd continued in use in medieval Europe. Safflower, extracted from the floret heads of the thistle, Carthamus tincton'us, is still used in India although i t has been replaced in Europe and the Mediterranean area where it formerly enjoyed wide use. The most ancient yellow dye, weld, from the dried plant Reseda luteoh, was widely used in Gaul and northern Europe. Old fustic, which, when introduced by the Spanish, replaced weld in the 16th century and is still used today, comes from the wood of Chlwophora tinctora, a member of the mulberry family growing in the Weliest Indies and tropioal America. Young fustic, obtained from the stem and larger branches of Rhus wtinus, the smoke tree common in Asia, Europe, and America, was used in medieval Europe. Quercitron, a native American dye, is obtained from the ground inner bark of several varieties of oak. Still used in India and Asia Minor today, turmeric comes from the ground roots of the turmeric plant, Curcuma longa. Lac, braailwood, and orseille are naturally occurring redshade dyes. Used largely in Asis, lac is produced by the insect Coccus lama, which feeds an banyan and fig trees. Braeilwood
Courtesy of the A m e t i m Museum of Natural History, New York
K e r n - I ~ l e c t aon. Branch
(Caesalpina eehinata), growing in southeast Asia and Brazil, provides the dye of the same nameused to alimited extent today. The wood is powdered, moistened, and fermented for five weeks to give the red color popular in medieval Europe. Orseille, obtained from the heads of lichens, was known by the ancient Greeks. Its use today is limited, although it was once employed extensively in the Near East, whence it was introduced to Europe about 13W (10).
The Indians in North and South America used dyestuffs many centuries before the explorations of the Europeans. Cochineal and indigo were used by the prehistoric Peruvians to dye textiles. Native Indians on the west coast of Central America used the dye from the purpura shellhh to color yarn long before the landing of the Spanish in America. Indigo, logwood, coohi-' neal, brazilwood, fustic, orseille, quercitron, and other dyes shipped from the New World were to be found in European markets after the Spanish conquests. The Navaho Indians are famous for their colored woolen mgs and blankets. They acquired a knowledge of the art as a result of their forays on the Pueblos, probably in the latter part of the 16th century. The Pueblos, long skilled in coloring vegetable fibers for cotton goods and baskets, had, under the influence of the Spaniards, changed to sheep raising and applied their coloring and weaving techniques to wool fibers; it was in this connection that the Spaniardshad introduced indigotothem. The Navahos learned the Pueblo techniques and expanded them greatly. Navaho colors, except indigo, were all of local origin and reflected the beautiful pale yellows, browns, grays, tans, and rose of the Southwest Desert. An ink based on ferrous tannate and colloidal carbon was used for black and gray shades. It was prepared from yellow ochre, the pitch gum of the piaon tree, and the leaves and twigs of the aromatic sumac. The ochre was roasted until it turned brown and then heated to dryness with the pitch to give a black powder. This treatment reduced the iron in the ochre to the ferrous state and also formed carbon. After cooling, the powder was thrown into a decoction of the aromatic sumac (tannic acid) to give a rich blue-black fluid. Yellows in various shades were extracted from several of the local plants. Among these were the yellow flowering tops of rabbit weed (a memberof the aster family), the root of the dock plant (buckwheat family), the blossoms, leaves, and stems of actinea, and the entire plant of the owl's claw, lichen, and basin sagebrush. Shades of orange came from decoctions of canyaigre and lichen in conjunction with suitable auxiliary agents, such as alum, juniper ashes, and sumac. Rabbit weed gave a yellow-green if green portions of the plant and the yellow blossoms were used together. Browns were obtained from boiled extracts of alder bark, canyaigre root, root bark of the mountain mahogany, and the leaves, nuts, and hulls of the walnut tree. The Indian tribes of Wisconsin and the Great Lakes region obtained colors by boiling various parts of plants in water. Yellow was obtained from sumac roots and
JANUARY, 1942
from the spotted touch-me-not, ladies' sorrel, speckled alder, bloodroot, and gold-thread herb. The sorrel plant, black oak, and bloodroot were also used inmaking orange. An orange-red was obtained from bloodroot, and a dark red from hemlock bark. The hooked crowfoot herb, inner birch bark, and osier-dogwood bark were additional sources of red. An extract from old a;nd rotteumaple wood was the basis of purple. Brown was their favorite colyr. It was obtained from the speckled alder, the butternut, the hemlock, and the sweet gale shrub ( I , $ , 6,7,14-17). MORDANTS AND OTHER AUXILIARY COMPOUNDS
Auxiliary compounds must be used in conjunction with many dyes which cannot he applied directly to textile fabrics. These auxiliary compounds may be classified into three groups: .mordants which help to fix the dye to the fabric; compounds which develop the dye color; and compounds which facilitate dyeing technique. Quite often compounds in the f i s t group are also found in the second group since they develop the color as well as k i t . Included among compounds which bring out the dye color are various oxidizing agents which convert dyestuffs from the leuco to the color form. Organic acids are often used to break Umkages in certain stabilized diazo compounds which then can react with coupling components to produce the final color. Other compounds, which in the trade are commonly called "developers," like the naphthols, resorcinol, etc., actually form part of the dyestuff by a diazo reaction carried out directly upon the fiber. Mordants are indispensable to the dyeing industry because many dyes do not become fixed on given fabrics unless applied with a mordant. This is true to a greater extent of the chemically more inert vegetable fibers, such as cotton, rayon, and l i e n , than of the amphoteric protein animal fibers, such as wool and silk. Some mordants are colored compounds, but the color is not essential in the dye application. However, a given dyestuff will produce different colors depending upon the mordant used in applying it. The cloth may he treated first with mordant and then with dyestuff, or first with dyestuff and then with mordant; or the cloth may he treated simultaneously with both. In any case the result is chemical precipitation on the fiher of color complex from mordant and dyestuff originally in the soluble state. Knowledge of the use of mordants was acquired very early in history. Alum ohtained from local mineral deposits was used by the Asiatic Indians, American Indians, Egyptians, Chinese, and Greeks. Certain plants used in India for dyeing have been found to contain alum. One important use of alum was in dyeing with madder and chaya, especially in Indian calico printing and in Turkey-red dyeing. Alum also was used in dyeing with Tyrian purple. Tannic acid was very popular as a mordant. It was extracted from gall nuts and the bark of various trees,
Courtesy of
the American Museum of Natural Hiatorg. New Yo&
Oak L a . -
with G d l Nut.
from sumac in Sicily and America, and from the cadou fruit in India. The Hindus, ancient Greeks, and Ameri-' can Indians also used it. Medieval Europe employed it quite extensively. In the application of Tyrian purple, indigo, and other colors, urine was considered essential. It is noted in Pliy's writings as having been employed by the Greeks and by the Romans of Pompeii, and is known to have been used by the Aztecs of Mexico. The value of oils or fatty matter in dyeing was long recognized. Buffalo milk, which has a high fat content, was used by the Hindus in their process of dyeing with chaya root. Oils played a very important part in the famous Turkey-red dyeing process originated in the East Indies. Many other mordants were used in early times. Iron and calcium compounds, and also tartar, were important. The Hebrews used a soapwort and chalk bath. Peruvians employed aluminum- and caleiumbearing silicates and iron oxides for coloring with cochineal and indigo. Iron tannate was favored by many American Indian tribes. Ashes were used by the Navahos and by the many tribes of the Wisconsin and Great Lakes region. The latter are known to have employed various clays, iron-containing red and black earths from springs, grindstone dust (containing iron), and iron dust. The Turkey-red dyeing procedure may be taken as a n example of the complicated four-months-long procedure
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of mordant dyeing as i t was carried out several centuries ago. (Today, only about three days are required.) The principle involved is the formation on the fiber of an adherent lake of alizarin, with aluminum and calcium. Oil, often rancid olive oil, reacted chemically and kept the materials uniformly distributed over the fibers. (Modern methods employ "Turkey-red oil," a waterdispersible sulfonated castor oil.) Successive steepings in baths containing dung, sumac or nut galls, alum, and chalk led up to the first madder bath, with ox blood to help fix the color. There were further treatments with nutgall and chalk followed by redyeing. The final process was the "clearing process" in which potash boil and sunlight (and in later days treatment with tin salts) brought out the final brightness of the very popular Turkey-red color. Greece and Asia Minor were centers for dyeing yarn Turkey red, and large quantities dyed with this brilliant and lasting shade were sold in Europe during the 17th and 18th centuries. .Compounds used today as mordants include many substances: chromium salts; chromates; aluminum salts, such as alum, aluminum sulfate, and aluminum acetate; iron salts, especially of the ferrous variety; compounds of tin, nickel, and zinc; oils, such as castor and olive; and tannic acid. Chrome compounds came into use about the time of the introduction of alizarin and play a vital part today, particularly in dyeing wool. They form fast and beautiful colors with a large number of modern dyestuffs. Aluminum and iron salts are among the most important substances employed as mordants. They are used in coloring both cotton and wool. Many substances are used in coloring, not as mordants nor as developers, but to facilitate application of the color. Some act to disperse dyestuffsin the application medium, some to aid penetration into the fabric, some to effect uniform fabric coloration, and others even strip color from fabric too heavy in shade. In printing, materials such as starch, flour, gums like tragacauth, senegal, arabic, and karaya, and dextrin, with or without china clay, are used as thickening agents which body the printing paste to suitable consistency for printing and also prevent spreading of colors by capillary action from the designs printed. Albumin, casein, and glue are used similarly but have the additional property of fixing the color mechanically and even chemically to the fibers. Several of the substances referred to in the above outline of Turkey-red mordanting and dyeing act to facilitate color application besides fixing, for they aid in uniformly distributing the color over the fibers and prevent uneven dyeing. Recent developments have brought out a host of new products for improving dyeing techniques. Soap has long been considered indispensable in dyeing, for its action is to wet more readily the fibers being dyed and also help disperse the dyestuff, thereby insuring uniform level dyeing. But it has a serious drawback in that i t is chemically unstable; acids and hard
JOURNAL OF CHEMICAL EDUCATION
water render it useless and the sticky compounds resulting interfere with the dyeing. There have been developed many compounds with soap-like properties which will withstand acids and hard water, and these are useful, therefore, in dyeing. They include the sodium salts of sulfonated products, sulfated fatty alcohols, fatty acid esters, fatty acid amides, and various phosphates of soda. Many dyestuffs have a great afEnity for certain fibers to which they are ap$ed, and this must be controlled so that the more accessible parts of the material being dyed do not take up greater quantities of dyestuff than the sheltered parts of the fabric. Certain leveling agents for accomplishing this are on the market. They are complicated compounds and little is known about them. Some are based on cellulose waste liquors, one is stated to be a nonionic condensation product of octadecyl alcohol and ethylene oxide, and another is of the type of dodecylpyridinium laurate. Faulty dyeings are corrected with the use of stripping agents which remove most of the dyestuff from dyed materials. Reducing and oxidizing agents alone are effective with many dyestuffs, but not all. Cationactive long-chain quaternary ammonium salts have been found to be satisfactory for stripping colors which do not yield to reducing and oxidizing agents (1, 6, 7-9, 12-17 20). MODERN COLORS
The synthesis of the dyestuff, mauve, by Perkin in 1856, from compounds of coal-tar origin started the way for development and production of the great number of synthetic coal-tar dyestuffs now available. It was the first indication that dyestuffs could be obtained on a practical basis without resorting to vegetable, animal, or mineral sources for extraction of color. Some important milestones in this development of modern synthetic dyestuffs in addition to Perkin's work were the discovery of the diazo reaction by Peter Griess in 1858, the synthesis of alizarin already mentioned, the introduction of direct cotton dyestuffs in 1884 (Congo red by Bottiger), the discovery of sulfur dyestuffs in 1873 by Croissant and Bretonnihre, and the introduction of synthetic vat dyestuffs, of which indanthrene blue in 1901 by Ren6 Bohn was the first. These vat dyes were found to possess a fastness to light and washing far in excess of other known dyestuffs. Synthetic dyestuffs are available in a wide range of shades. They are superior in fastness and simpler to apply than the "extract" dyestuffs. In addition, they are cheaper, brighter, and possess greater color value than their predecessors. The coal-tar colon can be classified chemically, but it is advantageous from the dyers' viewpoint to group them according to method of application. Following is a list of the groups with notes on their respective application techniques, the finished dye job, and chemical classifications: Basic Dyes. Perkin's mauve is a basic dye. These dyes are so named because the actual coloring principle
JANUARY, 1947
is a base due to the presence of free or alkylated amino groups. Acids solubilize these colors in water. They are applicable to animal (protein) fibers, such as wool, silk, etc., without the use of a mordant because of affinity for the amphoteric protein. However, mordants such as tannin and alum are required for dyeing vegetable fibers, for example cotton. The basic colors generally are characterized by great brilliancy and high tinctorial strength, but poor fastness to light and also to washing. Basic dyestuffs include many compounds of the chemical classes triphenylmethane, diphenylmethane, acridime, indulime, oxazine, thiazine, aziue, and azo. Acid Dyes. This group is one of the largest in the field. Here the coloring principle of the dyestuff molecule is acidic in nature due to the presence of sulfonic acid groups. These dyes are generally marketed as alkali salts which are water soluble. Application is from an acid bath where the acid (sulfuric, formic, or acetic, etc.) promotes deposition of color on the fabric from the bath. Glauber's salt is used in the bath as a leveling agent, for it tends to strip color from the fabric being dyed and thereby prevents localized or uneven dyeing. These acid dyes have no affinity for cotton and are used only for animal fibers, such as wool and silk, where there is affinity due to the amphoteric nature of the protein fibers. Properties of acid dyestuff applications are exceedingly vaiable. Some come out very bright in shade, others pale. Fastness to light and to washing is quite different from one color to another. Acid colors may be members of the chemical ,classes nitro, mono-azo, dis-azo, nitroso, triphenylmethane, xanthene, anthraquinone, azine, and quinoline. Mordant or Chrome Dyes. As their name implies, members of this group of colors require mordants in their application-that is, they become insolubilised on fabrics only in conjunction with metallic salts. They are found in the chemical classifications anthraquinone, mono-azo, dis-azo, oxazine, triphenylmethane, nitroso, oxyquinone, and xanthene. As a rule mordant dyestuffsare dyed on wool and silk, and the mordant used is a chromium compound. These chrome color applications are fairly fast to light and washing. Madder, the earliest known mordant dyestuff, is an anthraquinone (alizarin) dyestuff. Alizarin dyestuffs, to some extent, still are dyed on cotton with a calcium aluminum mordant. Direct Dyes. The singular point about this class of colors is that applicat.ion to vegetable fibers does not require the use of a mordant. Glauber's salt is used in the dye bath to facilitate dye exhaustion-that is, it hithers color take-up by the fabric. Congo red was the &st direct dyestuff, and much development followed its discovery, so that there now is a very large range of colors available. Color fastness to acids, light, and washiig in this group varies with the dyestuff used. Various dis-am, tris-azo, tetrakis-azo, stilbene, thiazol, and dioxazine comoounds make UD the direct dvestuffs group. Sulfur Dyes. This class of colors is also applicable to
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cotton, rayon, and other vegetable fibers without the use of a mordant. On the whole, shades are duller than those of direct dyes, but fastness to light and to washing is superior. These sulfur-containing dyestuffs are made by fusing together alkali sulfides and organic amino or nitro compounds. Little is known of the reactions in their preparation or their chemical constitution because of difficulty in isolating them in a pure state. Sodium sulfide and soda ash are used to dissolve them in the dye bath forming leuco compounds, and the color is then developed by oxidation. Vat Dyes. These represent, on the whole, the best dyestuffs available to the textile industry. They are complex in chemical nature and rather difficult to apply, but their brightness and fastness to light and washing are excellent. Vat dyes are so named because, like indigo, which was the fist vat dye known, they must be reduced to the soluble leuco (often colorless) form before they can be applied, and this reduction is carried out in vats. Indigo in the early days was reduced in fermentation vats and this technique still is used occasionally. For the most part modern dyeing pritctice makes use of sodium hydrosulfhe for conversion to the leuco form. After application to the fabric, the color is brought out by oxidation in air, by bichromate and sulfuric acid, sodium hypochlorite, sodium perborate, etc. These dyes belong to three chemical groups-anthraquinone, indigoid, and sulfide. Generally vat dyes are applied to vegetable fibers. Indigo is applied to wool as well (9, 19, $0). PIGMENTS
During the past decade there has been an important trend toward decorating textiles with pigments in place of dyestuffs. A pigment is a color which will be applied in the insoluble state. A dyestuff is color dissolved in a suitable medium for application from solution. Dyestuffs become pigments when they are applied from a medium in which they are insoluble or when they are precipitated onto the substance they are coloring. The use of pigments for textile decorating is not new. The Egyptians employed pigment paints to decorate their mummy cloths with hieroglyphics and fignres of gods many centuries before the Christian Era. American Indim tribes applied color to their fabrics of vegetable origin by rubbing in ochres and earths. They generally used three colors-hematite or some other iron-oxide red, yellow ochre, and blue or green from copper sulfate. Carbon was an essential component of the Navaho black application, and was prepared by roastiig pifion pitch with ochre. The salmon pink in Navaho fabrics was obtained by boiling the yarn in water from clay-red-colored rain puddles on the mesas of the Southwest. Pigments were the colorants for the &st textile printr ing pastes known to have been applied in Europe. This was in the 12th century by the monks in the abbeys of the lower Rhine. German printers used pigments through the 17th century until competition with fast
JOURNAL OF CHEMICAL EDUCATION
dyestuff prints from England and Holland forced them LITERATURE CITED to turn to dyestuffs. Italian cloth printmg of the 14th (1) AMSDEN,C. A,, "Navaho Weaving-Its Technique and century employed pigments, such as gronnd charcoal, History," The Fine Arts Press, Smta h a , Calif., 1934, saffron, logwood, verdigris, red lead, vermilion, and inchaps. V and VI. I n cooperation with the Southwest Museum. digo. These pigments were ground in liquid varnish (2) BENDER.M., Interchem. Rev., 4, 75-87 (1945). and block-printed on the fabric. (3) BORN,W., Ciba Rev., 4,106-29 (1937). During and after the 18th century the use of pigments (4) BORN,W.. ibid., 7, 206-27 (1938). for textile decorating declined to a role of little signifi(5) BRYAN,N. G., S. YOUNG,IWD C. K. SHIRLEY,"Navaho Native Dyes-Their Preparation and Use," a publication cance because such applications were comparatively of the Education Division of the U. 8. Officeof Indian poor in wash-fastness and stiffened the fabric. This M a i m U. S. Department of Interior. Februaw 10. 1940. was due to the inadequacy of the substances (natural C~onzoT,H., "painted and Printed Fabrics," ~ k r o p o l i t a n vegetable gums, glue, albumin, starches, varnishes, etc.) Museum of Art, New York, 1927. employed to fix pigment to fabric. F., ''Uses of Plants by the Chippewa Indians," DENSMORE, 44th Annual Report, Bureau of American Ethnology, The reason for present-day popularity of pigments in 369-74, U. S. Government Printing Office,Washington, coloring textiles is threefold. First, new synthetic D. C., 1928. resins have taken the place of the old natural gums, etc. ' FABER, G. A,, Ciba Reu., 9,284-90 (1938). These resins are fast to washing and resist alkali solu"The Principles and K m c w , E., AND J. B. FOTAERGILL, tion; they withstand dry cleaning and scrubbing, are Practice of Textile Printing," 3rd Ed., C. Griffin & Company, London, 1936. not affected by light over long periods of .time, and, LEGGETT, W. F., "Ancient and Medieval Dyes," Chemical owing to their plasticity, impart a minimum of stiffness Publishing Company, New York, 1944. to the fabric. Secondly, an emulsion technique was deLEIX,A., Ciba Rev., 1, 19-21 (1937). veloped which made possible discrete application of the P E R C I VMAC ~ , I., "The Chintz Book," Frederick A. Stokes pigmented resin throughout the fabric, and this absence Company, New York, 1923. SCEAEFER, G., Ciba Rev., 39, 1398416 (1941). of continuity helps to minimize stiffness of fabric. SMITH,H. H., "Ethnobotany of the Menomini Indians," Finally, recent research has introduced a variety of new Bulletin of the Public Museum of the City of Milwaukee, pigments, fine in particle size, brilliant in color, and 4, 1-174 (1923). extremely fast to washing, light, and dry cleaning. SMITH,H. H., "Ethnobotany of the Meskmki Indiana," Phthalocyanine blue and phthalocyanine green, which ibid., 4, 175-326 (1928). SMITH,H. H., "Ethnobotany of the Ojibwe Indians," r W . , cannot be applied readily to fabric from dyeing solution, 4, 327-525 (1932). are most noteworthy in this regard. Owing to their VNLLANT,G. C., "A~tecs of Mexico--Origin, Rise, and high color value, a minimum amount of pigment is Fall of the Aztec Nation," Doubled%y,Doran & Comnecessary for coloring, and the fabric is not loaded up pany, Garden City, N. Y., 1941. with pigment solids or resin binder (1, 8, 6, 6, 18). "Brief Guide to the Western Painted, Dyed, and Printed At the present time the greatest strides in the textileTextiles," 2nd Ed., Victoriaand Albert Museumurn-De~artment of~extiles,1938. dyeing industry are being made in the use of vat dyes "Dyeing withCoal WHITTAKER, C. M., AND C. C. WILCOCK, and pigments. An even wider range of hues and Tar DyestutIs," 3rd Ed., D. Van Nostrand and Company, greater improvements in fastness to light and washing, New York, 1938. as well as simpler methods of application, are in store W H ~ ~ E C.R M., , m C. C. WILCOCK,ibid., 4th ed., for the postwar years. D. Van Nostrand and Company, New Yark. 1942.
