DYEING is the art of colouring in a permanent manner porous or absorbent substances by impregnating them with colouring bodies. Most vegetable and animal bodies are porous or absorbent, and can be dyed ; some minerals also, such as marble, can absorb liquid colouring matters; but the term dyeing is usually confined to the colouring of textile fibrous materials by penetration. The superficial application of pigments to tissues by means of adhesive vehicles, such as oil or albumen, as in paiutiug or in some kinds of calico-printing, is not considered as a case of dyeing, because the colouring bodies so applied do not penetrate the fibre, and are not intimately incorporated with it. The mere saturation of textile fibre with a solution of some coloured body and subsequent drying do not constitute a case of dyeing, unless the colour becomes in so far permanently attached to the fibre that it cannot be washed out again by the solvent employed or by common water. In the present article dyeing will be considered only with relation to the vegetable and animal fibrous substances which are commonly used in clothing or furniture,the less important arts of dyeing feathers, skins, ivory, wood, marble, dec, being left over for treatment under other headings.
That dyeing was practised in the most ancient times is abundantly proved by the frequent mention of dyed colours in the oldest extant writings; that it was not a common art seems apparent from the uses to which coloured garments were devoted, and the distinction which they conferred upon the wearers. It is probable that such definite and bright colours as the " blue, and purple, and scarlet" mentioned several times in the book of Exodus, as well as the Tyrian purple so often referred to by Roman writers of the Augustan age, were so costly as not to be available for general and common use. Pliny is the only one of the older writers from whom we might have expected some account of the processes of dyeing employed at his time ; but, except a reference to two or three tinctorial substances, and a description of a process of obtaining several colours by one dyeing operation, which he saw practised inEgypt (see CALICO-PBINTING, vol. iv. p. 684), there is nothing detailed in his writings ;he in fact formally excuses himself from entering upon the subject as one not worthy of his atten-tion. The Tyrian purple is the only dye treated of at some length in Pliny and contemporary authors; its discovery and employment gave wealth and prosperity to Tyre and Sidon more than 1000 years B.C. In the days of the Roman conquests in the East it was reserved under penal statutes for imperial use; its production then declined, and eventually both the material and the art of using it were lost. From Pliny's description, modern investigators were enabled to rediscover the shell-fish which yielded the dye, but the colours furnished by it were neither so bright nor so permanent as those obtainable from much less costly dyeing materials ; and there is reason to conclude that the most brilliantly tinted garments of an Egyptian priest of Isis or Osiris, or the mantle of a Roman emperor, were poor and dull in hue compared with those within reach of a domestic servant of the present time.
From many independent sources Homer, Strabo, Herodotus, &c,it is clearly shown that the manufacture of coloured tissues was carried on by the Oriental nations. A knowledge of the art spread slowly westward, but there are few records of its existence to be found from the time of Pliny to about the 13th century. It would appear that the Jews held the secret or the monopoly of the dyeing art during this long period. According to Mrs Merrifield, Benjamin of Tudela relates that when he visited Jerusalem between 1160 and 1173 he found only 200 Jews resident in that city, and these were all engaged in wool-dyeing, which trade was entirely in their hands. Beckmann shows that at the same epoch the art of dyeing in Italy was principally carried on by Israelites. It is in Sicily that we can first distinctly discern the practice of dyeing in Europe ; afterwards the Italians generally practised it; and in the 13th century dyers formed important guilds in Florence, Venice, and other cities. It is not to be supposed that the art of dyeing was ever completely lost; the records of particular seats of the art only indicate that at such places some special excellence had been acquired which gave them a higher reputation than was enjoyed by others. The domestic records of all modern nations speak of dyers and dyed cloths. Among the ancient laws of Ireland are some which lay down the number of colours that may be employed in the dress of various classes of society, the monarch alone being permitted to wear seven colours ; from which it may be inferred that if the Irish at a very early period were not dyers, they at least had variously dyed garments. Similar facts can be adduced of all countries that possess an early literature.
From the perishable nature of textile substances and their comparatively small intrinsic value, very few ancient examples of the dyer's art have been preserved. We have, however, one account of a cloth containing dyed yarn which may have been in the dyer's hands in Egypt 1000 years before the Christian era ; and we have still in good preservation ecclesiastical vestments containing dyed silks which are certainly 600 to 700 years old. The late Mr Thomson of Clitheroe examined numerous mummy cloths, some of which had a border of blue and fawn-colour made by coloured threads introduced into the loom. The blue^ upon examination, was proved to have been dyed with indigo; other specimens of mummy cloth of a reddish colour appeared to have been dyed with safflower, though this colouring matter could not be recognized with the same certainty as indigo. Dr Rock, in his catalogue of the textile fabrics in the South Kensington Museum, attributes many of the church vestments there preserved to the 12th and 13th centuries, and in these can be seen silks of all the colours known to dyers up to the middle of the present century, which, though in most cases changed and faded, still present sufficient evidence that dyeing, upon this material at least, was successfully practised in the Middle Ages. It is interesting further to note that in inventories of vestments of the 13th century the silks in the vestments are often designated by their colours, as in a chasuble at St Paul's, London, 1295, which is set down as "purpureo aliquantulum sanguineo," of a purple inclining to blood red. This, as Dr Rock says, is intelligible; but other definitions are not, as " pannus Tarsici coloris," a Tarsus-coloured cloth; it can only be conjectured that it was a purple dyed at Tarsus, and something like the Tyrian purple ; sky-blue silk is named " indicus," probably because it was dyed with indigo.
The earliest account of the processes and materials used by dyers is to be found in a collection of manuscripts in the French National Library, No 6741, known as the manu-scripts of Jehan le Begne. These mostly refer to the art of painting and the making of artists' colours and the modes of applying them, but some describe the preparation and use of dyes. The most interesting of these manuscripts is by Jehan Alcherius (Le Begne was only the copier or com-piler), which from internal evidence cannot be dated later than the year 1410, and some parts of which refer to a period at least thirty years earlier. Among the colouring matters and mordants there mentioned we find iron (the dust or mud from grindstones on which knives are ground) dissolved in vinegar and mixed with alum, green copperas, and gall nuts prescribed as a black colour ; and methods are given for the use of Brazil wood, litmus, indigo, in con-junction with lime and honey, verdigris, alkalies, oxide of tin, kermes, <fcc., much in the same way as those employed four centuries later by dyers and calico-printers. There are also eleven receipts for preparing colours, for painting on cloth to imitate tapestry,examples of which (toiles peiiites) of the 15th century were exhibited in Paris in 1876. Curiously enough, a certain Fleming named Theo-dore in 1410 brought these receipts to Alcherius from London, where they were in regular use. They are all chemical dyes, and seem to be the prototypes of the same class of colours employed long subsequently by calico-printers in England and other countries.
The first printed account of dyeing processes was an Italian work. It is referred to under the title Mariegola dell' arte dei Tintori, published at Venice in 1429. The writer has never seen a copy of mis work, nor does it appear that any exists in the chief libraries of Europe ; an enlarged edition was published in 1510. In 1548 Rosetti wrote an account of dyeing, which was also published at Venice. Copies of this are not very scarce; it is the only one of these early books which is actually known. The so-called Bolognese manuscript translated in Merrifield's Ancient Practice of Painting, is preserved in the eonvent of St Salvatore at Bologna, and is said not to be of later date than the middle of the 15th centurythat is, about 100 years anterior to the date of Bosetti's work. In this manuscript, in addition to the materials enumerated by Alcherius, mention is made of woad and methods of making indigo from it; of indigo imported from India, called bagadon and bagadel; of sumach, gall nuts, and lac; of the berries of buckthorn, similar to the Avignon or Persian berries, to be used for yellow; and of Brazil wood or verzino, sandal wood, and madder for red; and archil for purple. The use of nitric acid to give a yellow colour to silk, and of alum for preparing and mordanting that material, and the subsequent dyeing of it by Brazil wood, are also clearly pointed out. The receipt No. 362 of this manuscript is of interest as showing that the Italian dyers early possessed the method of dissolving indigo by means of the action of honey and quick lime upon it, and used the solution for the blue required in dyeing silk green.
It is very clear, then, from these accounts, and from numerous existing samples of coloured stuffs, that dyeing was well understood in Europe in the 15th century, and that the materials at the command of the dyer were sufficiently numerous and varied to enable him to produce all desired shades of colour. The improvements which took place in the dyeing art from this time until the commence-ment of the present era of artificial colouring matters were no doubt important in detail, but not very striking in principle.
The discovery of America was soon followed by the intro-duction of cochineal (see vol. vi. p. 97), but this did not enable the dyer to produce any new colours, since it differed from the ancient kermes, frequently called grana or grains, only in being ten or twelve times as rich in colouring matter. Logwood or Campeachy was also an introduction from the New World, and greatly enlarged the power of the dyer, though, from the looseness of the colours it yielded, it brought his art into some disrepute; it was in many respects a new colouring matter, but eventually settled down as the principal ingredient in the common black dye. In mordants, the discovery in Holland in the 17th century of the use of solutions of tin in acid, especially for the scarlet dye with cochineal, was one of the greatest utility. The gradual introduction of the acetates of aluminium and iron +.o replace the respective sulphates was of more importance to calico-printing than dyeing proper. At the close of the last century Dr Bancroft discovered and introduced quercitron bark from America for dyeing yellows, and this, from its superior richness and less cost, displaced other materials used for that purpose. Of the natural dyes intro-duced in the present century probably the most important is catechu. The discovery of the use of bichromate of potash as a mordant for woollen goods belongs to the latter half of this century, and has been of the highest benefit to the dyer. We shall not speak in detail of a number of dye-stuffs used by dyers of the present day, which were probably unknown to their predecessors, because most of them are only varieties of what have been long employed. Such, for example, are valonia, divi-divi, and myrobalans, which have no properties different from galls or sumach, and the different red woods, which are merely varieties of the anciently known Brazil woods.
Artificial Colouring Matters.In the year 1858 com-menced the discovery and application of a series of artificial colouring matters, wdiich have created a distinct era in the history of dyeing. Up to that date the colouring matters used in dyeing were either the spontaneous productions of nature or simple preparations of the same. An exception, however, must be made to this statement in respect of Prussian blue and the so-called suluhate of indigo, which have been largely used as colours in dyeing since the middle of the last century, and are as truly products of art as any of the modern creations of chemistry. The purple of murexide had only a brief existence as a dye. Mr Perkin was the first to practically produce a dyeing material from aniline, the well-known mauve or purple sha'de so much in vogue for several years, for a history of which see vol. ii. p. 48 of the present work. Other discoveries rapidly followed, and in the course of a few years it may be said that a hundred patents were taken out for methods of making artificial colouring matters from aniline and its homologues; these alkaloid bases, under the transforming hands of chemists, supplied the dyer with every shade and hue which could be desired. Up to 1869 the artificial colours were of one general family, and had many characters in common; they were very brilliant, very easily applied on fibre of animal origin (silk and wool), required no mordant, and for the most part were very loose and unstable. Imitating more or less closely the colours obtained on tissues from natural colouring matters, they had no similarity of chemical composition, and were in every other respect fundamentally different from them. In 1868 two German chemists, Graebe and Liebermann, by means of a severe synthetical investigation, succeeded in transforming anthracene into alizarin, the latter being identical in chemical composition as well as tinctorial properties with the colouring matter of madder, one of the most anciently known and most valuable of all natural dye-stuffs (see vol. i. p. 577). This was the first instance in which chemistry had produced one of the old and well-known colours of the dyer; in a short time after its discovery it was made practically available for the trade, and has at this date (1877) almost entirely driven from the market the native product, accomplishing a revolution which has no parallel in the history of colouring matters, and which is one of the most signal triumphs of modern chemistry. Other natural colouring matters have since then been produced by art, such as indigo and archil, but from some difficulties in their manufacture they have not yet become commercially avail-able.
Mechanical Improvements.In the art of dyeing, steam power has proved no less serviceable than in other important industries. Its applications are not further alluded to in this article, but in the article upon CALICO-PRINTING (vol. iv. p. 684) some illustrations of modern machinery may be seen.
GENERAL PRINCIPLES OF DYEING.
Although many eminent chemists have worked and written upon the subject, there still remains much difference of opinion as to what actually takes place in dyeing operations. The following general account of the chief cases of dyeing will illustrate the principal methods in use, and serve as an introduction to a description of actual processes practised in dye-houses. Afterwards, the attempts made to con-struct a general theory will be briefly considered. The simplest cases of dyeing are those in which only two substances are employedthe fibre to be dyed and the colouring matterand where the process of dyeing consists in nothing more than leaving the two materials in contact for a certain time at a convenient temperature. Of natural colouring matters few can be practically used in this simple way without some previous chemical treatment. The arti-ficial colouring matters from aniline, however, illustrate this kind of dyeing very well. To obtain the finest shades of mauve, magenta, purple, and numerous other colours upon wool and silk fibre the whole process consists in placing the material in a solution of the requisite colour and of sufficient quantity to give the desired shade; it absorbs the colour, becoming dyed, while the solution is rendered nearly colourless. During the process the fibrous material is kept in a constant state of movement, so that the dye solution shall have equal access to all portions, the temperature employed and time allowed being regulated according to the necessities of the case. The colour absorbed by the fibre has entered into an intimate state of combination with it, since it cannot be washed out again; a true dyeing has taken place. Besides the aniline colours, the older artificial dyessulphindigotic acid, picric acid, and one or two othershave the same property of combining directly with wool and silk.
There are other cases of dyeing closely resembling the foregoing, in which the resulting dyed stuff may be considered as being a binary compound of fibre and colouring matter, but in which the methods of application are less simple. These may be taken generally as consisting in the use of materials or processes which bring a previously insoluble colouring matter into a soluble state ; thus the pink colours of safflower are obtained by the action of an alkali; and the dyes yielded by archil, arnotto, and indigo are also the result of the action of solvents. It is possible that during the process of solution important internal changes may take place in the composition of the above dyes, but if so, they are only of a temporary nature, for there is no reason to sup-pose that the colouring matter attached to the fibre differs in chemical composition from that which is free.
With regard to nearly all other colouring matters, the above simple processes are quite powerless to induce a permanent combination with the fibre. Let wool or silk be immersed at boiling temperature in decoctions of any of the best known natural dye-stuffs, such as cochineal, logwood, madder, quercitron bark, &c, and then washed in water, it will be found that the fibres are simply discoloured, or stained of no definite shade ; they have taken up but a small portion of colour from the decoction, and no real dyeing has taken place.
Use of Mordants.To obtain permanent dyes from the great majority of native colouring materials the intervention of another class of bodies entirely different from either fibrous or colouring matter is found necessary ; these bodies are called mordants. The term mordant is found in Latin and Italian manuscripts of the 12th and 13th century, as the name of an adhesive composition by means of which gold leaf could be attached to wood, marble, or metal ; early dyers appropriated the word to designate a substance by means of which colouring matters could be made to adhere to fibre, and it has been retained in that sense in all modern treatises upon dyeing.
The chief mordants used in dyeing are salts of aluminium, iron, tin, chromium, copper, and a few other metals. When a decoction of a colouring matter, say logwood or cochineal, is heated with a small quantity of a properly chosen salt of one of these metals, it is found that the colouring principle loses its solubility, forms a combination with the metallic salt or its bases, and precipitates to the bottom of the solu-tion, leaving the supernatant liquid nearly or quite colourless. The precipitate is usually called the " lake " of the particular metal and colouring matter, which are probably in a state of chemical combination ; the lakes are insoluble in water, and are only split up again into their constituents by the action of somewhat powerful chemical agents.
Fibre cannot usually be dyed by means of ready formed lakes, for the reason that they are insoluble in water and not easily soluble in any menstruum which can be safely applied to such material; they are themselves of too coarse and gross a nature to penetrate the fibre, and when applied to it rest for the most part on the surface, and are therefore easily removable by washing or mechanical friction. It is known, however, that for some colours in calico-printing lakes can be applied, but that is only in conjunction with acid salts and at a high temperature, by means of which a sort of solution is obtained while in contact with the fibre itself. The art of the dyer consists in so arranging these three elementsfibre, metallic salts, and colouring matter_ that he may obtain the formation of the insoluble coloured lake in the body of the fibre itself, whereby either by the lake being mechanically retained or chemically combined the fibre is permanently coloured.
Application of Mordants.There are three principal ways in which the mordant and colouring matter can be put into contact with the fibre, the developments and modifications of which constitute the whole art of dyeing.
1. By the first method, which is by far the most common, the fibrous matter is separately impregnated with the mordant, which is by various means decomposed, so as to deposit its base in an insoluble state upon or within the fibre, and afterwards the colouring matter is applied. Take, for example, the case of dyeing a common bla.ck from logwrooa upon calico, which has no affinity for the colouring matter of the logwood. The first process is to pass the calico through a hot aqueous solution of sulphate of iron, some-times mixed with acetate of iron, and to remove the excess by pass-ing the cloth through rollers ; the cloth, either previously dried or not, is then passed through a mixture of lime and water which has the effect of decomposing the iron salts and liberating oxide of iron. A washing in water to remove the excess of lime or any loosely attached oxide of iron prepares the calico for coming into contact with the logwood. The calico, which has now a buff colour, owing to the attached mordant of oxide of iron, when placed in a hot decoction of logwood speedily acquires a dark hue and in about half an hour has become dyed of a dense black colour, and, when smoothed and finished, forms the common black calico of the shops. A variety of other cases might be adduced; woollen cloth boiled for some time in bichromate of potash solution acquires a certain amount of a salt of chromium, which enables it to take a black colour from logwood, and other colours from other dye-stutfs. Woollen, boiled with salts of tin, is enabled to dye up a brillant scarlet in decoction of cochineal; boiled with alum, it will take a great variety of colours in various dye-stuffs. The practice of calico-printing illustrates in a very forcible manner the action of mordants ; by the aid of apparatus described in the article upon that subject, portions of a piece of calico are impregnated with mordants, and these portions alone acquire colour from the dyeing solution, and thus designs or patterns are produced upon a white ground. The most usual method of impregnating the fibrous matter with mordant, consists in heat-ing it with the required metallic salts, and it will be seen hereafter that easily decomposed salts are those preferably used ; or substances such as chalk, alkalies, or tartar are added to some more stable salt, such as alum, to induce the formation of comparatively unstable compounds, which, under the influence of a high temperature and contact with fibrous matter undergo decomposition,the metallic oxide or some basic insoluble compound of it becoming intimately combined with the fibre, which is then said to be mordanted.
2. A second method, less general than that above described, is to apply the colouring matter before the mordant. It is resorted to only with heavy goods which absorb a large quantity of liquid, or with light colours upon other fabrics ; dyes produced in this way are super-ficial in their character, and not so permanent as those produced by the first method. In dyeing by that method it is in many cases cus-tomary to add a small quantity of mordant to the dye-bath when the process is quite or nearly finished, or to pass the dyed goods, as a final operation, through a diluted mordant.
3. A third method is to apply the mordant and the colouring matter together to the fibrous substance. In common piece-dyeing in weak liquids this plan is seldom followed, on account of the ten-dency to form insoluble lakes in the solution, which, depositing only on the external part of the fibres, give inferior results, alike as to sta-bility of colour, depth of shade, and evenness or regularity of the dye. In calico printing or in padding, this method is of extended appli-cation and the inconveniences experienced in common dyeing are not perecptible, owing to the greater concentration of the mordant-ing salts and the use of thickening matter. Lakes are very probably formed to some extent during the preparation of the mixtures, but, the combination taking place in the presence of a fluid made viscous with gum or starch, the insoluble lake is in an extremely fine state of division; in such a mixture there is always present an acid or an acid salt, such as acetic acid, oxalic acid, tartaric acid, or alum, chloride of tin, cream of tartar, or binoxalate of potash. These tend, in the first instance, to restrain the formation of a lake, and after-wards, when the fibre and the mixture of mordant and colouring matter are submitted to heat, as in the process of steaming or stoving, facilitate the solution of any lake formed, which thus finds entrance into the fibrous matter, and there undergoes combination with it, owing to decomposition of the mordanting salts, a true dyeing taking place.
PRACTICAL DYEING PROCESSES.
By the foregoing preliminary observations the reader will have been prepared to comprehend the rationale of the practical processes of dyeing. In order to give a fairly comprehensive account of these, it has been found con-venient to take the colours in the old arrangement of simple and compound colours. Bed, blue, and yellow are supposed to be simple or primitive colours; the methods of obtaining these being given, then follow the colours from mixtures of two of the elementary colours, as green from yellow and blue, orange from red and yellow, and purple from red and blue. The colours not included in the above, and in the dyer's philosophy made by mixing the three elementary colours, red, blue, and yellow, in different proportionsnamely, the browns, greys, and chocolates, and blackwill be conveniently treated of after those supposed to result from the mixture of two of the primary colours.
This arrangement, though perfectly arbitrary, is both convenient and consistent as far as regards dyeing; for though modern discoveries in optics may show that pure blue and yellow do not make green, and may in other respects disturb the older ideas concerning primitive and secondary colours, yet the dyer has sufficient justification for retaining the old system, because he can show that his blue and yellow always make green, and that the proper mixture of the so-called simple colours produces a compound shade which can be calculated beforehand from the propor-tion of the respective colours employed.
The most important of the red colours produced by dyeing are obtained from cochineal and from madder, the former being used for woollen and the latter for cotton goods. They are both old colours, and have arrived at their present excellence by slow degrees ; they are deep and brilliant, and, as far as regards permanency, hold the highest position among all dyed colours. The processes employed are instructive as illustrating the diversity of treatment required by different fibres and colouring matters.
Used upon wool from cochineal.Let it he assumed that the shade of red required is fine scarlet, such as is worn by officers of the British army, and that the woollen cloth is of finest quality. The cloth first requires purifying from all the adventitious substances which it has acquired in the process of manufacture, in order to prevent irregularity and unevenness in the shade of colour ; this is done by methods described in the article BLEACHING. The only materials required to produce a fast scarlet upon wool are oxide of tin and the colouring matter of cochineal, but it requires much practical skill to bring them into contact properly. After the cloth is cleaned, and while it is still wet from its last washing, it is mor-danted by boiling it in a solution of a salt of tin with or without cream of tartar. The parts of the boilers not in actual contact with the fire are frequently constructed of pure block tin, or at least all parts out of water should be of this metal, or else protected by wood, or the dyeing vessel should be made entirely of wood and heated by steam pipes ; for if the cloth containing the acid solution of tin comes in contact with a copper or brass surface it acquires a stain which afterwards dyes up an impure colour. What takes place in the course of boiling is that eventually a certain portion of tin, probably in the state of stannic oxide, becomes fixed upon or within the fibres of the wool, and this in a perfectly uniform manner. The tin not in intimate combination with the wool, or held merely by capillary attraction, is washed off by water before the cloth is brought into contact with the colouring matter.
The mordanted cloth is now brought into a boiler containing finely ground cochineal diffused through a sufficient quantity of water, to which it is usual to add some more tin mordant and tartar ; the cloth is turned continually to prevent folds or creases from interfering with the free access of the dye to all parts of it. The contents of the boiler are heated to the boiling point, and in half an hour or so the liquid becomes nearly colourless, and the cloth is found dyed of a bright red.
The above may suffice to furnish a general view of the procedure usually followed, and to illustrate the principles involved with regard to numerous other dyes besides cochineal. To give the general reader a further idea of certain operations practised in the use of that colour (and the description applies more or less to others), the following particulars may be noted.
T/ie tin mordant used for scarlet on wool.It is now 200 years since the discovery was made of the use of tin with cochineal for dyeing scarlet; it might be thought that by this time the exact kind and quantity of tin solution to be used would have been settled; there exists, however, the greatest diversity upon this point among practical dyers. The two salts of tin met with in commerce, de-signated by chemists stannous and stannic chlorides, have received various names from dyers. Crystallized stannous chloride is generally known as " tin crystal;" the solution of the same as muriate of tin. A single muriate and a double muriate of tin are also distinguished, the difference being in the degree of concentration; but in some parts of the country double muriate of tin is the name given to a solution of stannic chloride, elsewhere called bichloride of tin, and a good deal of confusion is sometimes caused by the various uses of the trivial names of the solution of tin. Experi-ence teaches the dyer that there are scarcely two dye-works in the world in exactly the same condition with regard to either water and air, or apparatus, or quality of materials, and that the nature and quantities of drugs, mordants, and dye-stuffs used, and the duration and temperatures of the operations which secure admirable results in one place are altogether unsuitable in another. It is, however, clear that by far the greater part of the variations introduced by practical dyers are not really founded upon necessity. Thus although the best colours can be obtained by the use of simple tin solutions manu-factured on the large scale, in nine cases out of ten the operative dyer of scarlet insists upon preparing his own solution, and pretends that he employs special methods aud preparations without which it would never be fit to use ; and hence a countless number of tin solutions are in use.
Tin spirits.The solution of tin used by dyers for the scarlet and for many other colours upon wool, silks, and cotton, are commonly called spirits, or "tin spirits," a name which is very old, and appears to have originated in the use of nitric and hydrochloric acids to dis-solve the tin, which acids were formerly, and are evenat present, called spirits of nitre and spirits of salts. One solution which is a favourite, from the ease with which its metal goes to the wool, is the so-called nitrate of tin (sometimes called " bowl spirits," from being prepared in an earthenware bowl) made by dissolving thin metallic tin in moderately strong nitric acid. This is an operation requiring great care and some experience to prevent the formation of insoluble metastannic acid; the tin is added by small portions and gradually, so that the acid does not become hot; the solution takes place quietly, inodorous nitrous oxide is evolved, and ammonia is formed. If the tin be added too rapidly to the acid, red fumes of nitric oxide are evolved, the liquid boils up, becomes thick from separation of metastannic acid, and is utterly useless as a mordant. This so-called nitrate of tin is a very unstable compound, decomposing spontaneously in a few days, so that it has to be prepared just as it is wanted; it is theie-fore not an article of commerce. The other very numerous "tin spirits " may be said to be solutions of tin in a mixture of nitric and hydrochloric acids ; but the latter acid is sometimes replaced by the chlorides of sodium and ammonium, the resulting mordant being essentially a stannic chloride mixed with stannous chloride. Closely woven and loose woollen fabrics, such as yarn and flannel, require different tin mordants, as some mordants are more quickly decom-posed than others. The result of using an easily decomposable mordant such as the nitrate of tin upon closely woven cloth would be the formation of a deposit upon the external fibres of the wool, the interior of the cloth being unaffected. For such cloth, therefore, a tin spirit which is only slowly decomposed, such as the muriate alone or mixed with tartar, must be chosen, so as to allow of a tolerably thorough saturation of the cloth before the breaking up of the mordant during the boiling. Here it may be observed that good, thick, and finely woven cloth which is dyed in the piece, that is, after weaving, is hardly ever completely dyed through; this can easily be shown by cutting through the cloth with a sharp knife, when the interior will be seen sometimes nearly wdiite and generally much paler than the exterior ; hence the preference which is given to cloth made from yarn dyed before weaving, the colours of which do not fade so readily as those of piece-dyed goods. Imperfection in the dyeing of the latter can by care, however, be reduced to a minimum, and in dark goods is hardly discernible.
Use of tartar along with tin mordant.The " tartar " of the dyer is a more or less impure form of the cream of tartar of the shops, or the acid potassium tartrate of chemists. It is in very general use for wool dyeing, and when employed with dye-stuffs plays the part of an acid, and could in fact be replaced by an acid ; in other cases, when used in mordanting, it no doubt acts as a salt, contributing to neutralize the strong mineral acids of the mordant, and rendering them more ready to decompose in the presence of the cloth. In a particular receipt for dyeing scarlet the proportions of materials are as follows:20 lb of tin solution, containing about 20 ounces of metallic tin dissolved in nitric acid, with the addition of a little common salt, are used to 100 lb of woollen cloth. Of the 20 lb of mordant, 13 lb are taken and mixed with a solution in water of 8 lb of crude tartar, and about 8 ounces of cochineal are added to enable the dyer to form a judgment of the progress of the mordanting. The ingredients having been boiled for a couple of hours, the cloth is rinsed in clean water and placed in another boiler, containing the residual 7 lb of mordant and 6 lb of ground cochineal, which are sufficient to dye up a full scarlet colour ; but if the scarlet is required to be very bright, or what is called "fiery" coloured, a further quantity of tartar is added ; this has the effect of somewhat reducing the depth of colour, and at the same time giving it a yellowish or orange hue, which for certain purposes is much desired.
Use of yellow in scarlet.It appears that Bancroft, who wrote about the end of the last century, was the first to suggest that the bright fiery scarlet, which the dyers found they could best obtain by using a large quantity of tartar, might be produced more cheaply by adding some yellow colouring matter to the cochineal, or by first dyeing the cloth a light yellow ; he tried the yellow from quercitron bark, and succeeded as far perhaps as was possible with that material. At any rate from his time it has been customary for dyers who do not aim at the highest degree of excellence in the scarlet colour to use a purified preparation of quercitron bark, commercially known as flavine, in conjunction with cochineal; other yellow colouring matters, such as fustic and turmeric, are also used. An admixture of these substances cheapens the cost of the colour, which can be made nearly equal in appearance to that obtained with cochineal alone, but it does not stand wear so well, and is more readily stained by various influences. The best scarlets are still dy ed exclusively with cochineal.
Scarlets on wool from lac-dye.The colouring matter of lac-dye is in its chemical properties and composition very similar to, if not quite identical with that of cochineal. As it is imported into this country from India, it is, however, less pure than average qualities of cochineal; and it is probably on account of its impurities that the dyer cannot obtain quite so good results as the best cochineal colours4 although if skilful he may approach them very closely. Having been submitted to a preliminary treatment with acid to free it from alumina and other earthy matters used in its prepara-tion, it is then applied exactly in the same way as cochineal. It is extensively used for a second class scarlet, and is believed to be somewhat more durable and stable even than cochineal. The red cloth so much used for military dress is reputed to be prepared mainly with lac-dye.
Crimson red on wool.This colour is also dyed with cochineal, but with a mordant of alum instead of tin. It is a far less important colour than the scarlet, and compared with it is dull and fiat; it is, however, rich and durable, and combines excellently with other colours.
The mordanting of cloth by means of alum, an operation of capi-tal importance for a large series of colours derived from all varieties of dye-stuffs, must now be noticed.
Aluming of wool.The method of mordanting with alum, generally called aluming, is practically a simple process, but the chemical principles involved have given rise to much debate amongst experimenters. The aluming is usually performed by boiling the wool for one or two hours in a solution of common alum mixed with tartar ; a certain portion of alumina, or, it may be, of some compound of aluminium, becomes thus intimately combined with the wool, and forms a basis upon which a coloured lake may be produced with solutions of colouring matters. The chemical conditions are somewhat different here from those which obtain in the case of mordanting with tin; for the disposition of tin salts in dilute solutions to decompose even spontaneously is so manifest that it may readily be supposed that some action on the part of the wool takes place which induces the formation of oxide of tin. The great apparent stability of alum caused the explanation of its action given by Thenard and Roard to be for a long time accepted. They held that it was absorbed whole or unchanged by wool, which retained it by some undefined power, so that it could not be removed by cold water, and required to be heated twenty times with boiling water to dissolve it out. In the light of modern researches this explanation may be safely rejected as erroneous. What appears to be the true state of the case was mainly brought out by experiments of Havrez, suggested by the celebrated Belgian chemist Stas, and supported by further knowledge of the properties of alum discovered by Tiehbourne and Naumaun. In fact, alum, contrary to what was formerly thought, is particularly liable to decomposition, even when not in contact with fibrous matters which might possibly have an influence upon it. Naumann has shown that by simply heating a solution of alum, saturated in the cold to its boiling point, an insoluble basic compound is soon produced, so that, after prolonged heating, as much as 25 per cent, of the alumina is precipitated, and the liquid is found to have become acid. _ Beyond this fact it is proved that wool when placed in a solution of alum, containing pure sulphuric acid, has the property of absorbing more acid than alum; this unequal absorption is attri-buted by Havrez to a kind of dialysis, which, together with the ten dency of the alum to decompose, sufficiently explains the deposition of alumina upon the wool. The action of tartar in aluming, accord-ing to the same authority, is that of an acid salt, and its addition in-fluences the nature of the mordant deposited in the same way as if an excess of alum were present, or as if other acid bodies, such as sulphuric acid, oxalic acid, &c, were added. The insoluble aluminous compound which separates from solution of alum on prolonged boiling in a glass flask could not act as a mordant, being indifferent or passive to colouring matters ; when deposited on fibrous matter it does not adhere, but can be washed off, or when dry may be shaken off like dust; this, therefore, is not the alumina mordant, nor do the researches of Havrez really point out what the alumina mordant is, though they are valuable and suggestive as showing under what conditions either a basic or an acid aluminous deposit is formed. With the former, which is unfavourable for dyeing, a blue colour is given with logwood, and a purplish red with Brazil wood; with the latter, the wool dyes up a violet with logwood, and a purer red with Brazil wood. The basic state of the aluming results, it is supposed, from the deposition of hydrate of aluminium upon the wool, and is caused by having too little alum or too much water,by boiling for too long a time, or by the use of salts which have a neutralizing action upon the alum. It is easily induced, when the weight of wool is more than 15 times greater than that of the alum. In other circum-stances the acid state results, in which the wool is said to fix first hydrate of alumina, and also hydrated sulphuric acid from the sul-phate of alumina. These conclusions of Havrez cannot, however, be accepted as final or satisfactory; and there is still much to learn upon the principles of aluming and mordanting generally.
The wool being successfully alumed acquires a crimson colour by dyeing in cochineal, but, as before stated, this shade is not of much value.
The shades of red between scarlet and crimson reds proper, or cherry reds, are also dyed with tin mordant and cochineal in nearly the same way as the scarlet; but in order to avoid a yellowish tone, the natural cochineal may be mixed with the manufactured or modified material know-n as ammoniacal cochineal.
Ammoniacal cochineal.This is made by treating ground cochi-neal with concentrated aqueous ammonia for several days ; the colouring matter undergoes important changes by this process, au amide is formed, and the effect upon the colouring matter is that tin mordants give with it no longer a scarlet, but rather a violet tone. Ammoniacal cochineal is much used in fine dyeing for pinks; and according to the proportion in which it is added to ordinary cochineal, the normal scarlet shade is gradually brought over to the red and even to the crimson.
Pink or rose colour upon wool.This shade is obtained from ammoniacal cochineal, mordanting previously in a mixture of tin solution, alum, and tartar ; the quantity of tin mordant used is small, the alum being the essential basis.
Other red colours upon wool.The colours mentioned above are from cochineal or its congener lac-dye ; there are several reds obtain-able from other colouring matters, which, though less important, are still worthy of mention.
Madder red upon wool.This colour is wanting in brightness, but it is valuable for its stability, and has at times been largely used for common red military cloth. As a basis for browns, chocolates, and other dark colours, it is very suitable when its com-paratively high cost is not an objection. To obtain madder red, the wool is boiled for two hours with a mixture of alum, tartar, and tin salt,3 lb alum, 1 lb tartar, and 4 ounces of the tin solution being taken for 10 lb of cloth; after boiling, the cloth is rinsed in water to remove uncombined mordant, and then dyed with madder, or preferably its derivative garancin, with addition of a portion of tartar; the dyeing may be accomplished in an hour, the depth of colour varying with the amount of colouring matter used.
Artificial alizarin on wool.By employing artificial alizarin somewhat better shades of colour can be obtained, and even pink colours of much solidity produced. A process for obtaining a fast red on woollen yarn, from alizarin, is as follows :boil 10 lb wool for an hour and a half with 1^ lb sulphate of alumina and 4 lb tartar ; rinse in water, and then dye with 6 to 7 ounces of artificial alizarin paste containing 10 per cent, of dry matter ; commence the dyeing cold, and gradually heat to boiling. Alizarin can be used as a basis for producing fast brown shades, by adding fustic and extract of indigo after the red has been developed, and if necessary, a further quantity of sulphate of alumina and tartar.
Red colours can also be obtained by using Brazil wood or other red woods instead of madder; they are, however, of a low class and sel-dom employed. Archil alone, without mordant, can yield a full crim son upon wool, but it is not very stable, and is, moreover, expensive.
Aniline reds upon wool. There are several artificial red dye-stuffs, which may be used for wool, but none possesses great excellence. The only one which resembles cochineal in its qualities is the recently discovered eosine ; this, with an alumina mordant, gives upon wool a very good imitation of cochineal scarlet, but an imitation only, for the colour fades rapidly in sunlight, and is easily washed out by soap and water. Substances similar to eosine, which have even still more recently appeared in trade, are called coccine and ncpaline; they yield beautiful but perishable red colours on wool and silk.
Red colours on cotton.Turkey red.Cochineal, which is so suit-able a colouring matter for wool, does not dye satisfactory colours upon vegetable fibres ; but from very remote times the Hindus have possessed a process for dyeing a brilliant and extremely per-manent red upon cotton fabrics by means of madder. This process travelled westward through the Levant into Turkey and Greece, the date of its introduction into Western Europe going no further back than the middle of the 18th century, at which period Greek dyers were induced to settle in France and make known the methods in use for the production of this much desired colour. The name Turkey red, or Adrianople red, was applied to calico dyed with it at the time that such goods could be obtained only from the East, and it still retains the name. So much was the colour esteemed that in 1765 the French Government circulated a pamphlet describ-ing the best known methods of dyeing it on yarns, and some years afterwards, the British Government paid a sum of money to a Frenchman named Papillon, for disclosing the whole process of obtaining it. The dyeing of Turkey red upon cloth and yam is now extensively carried on in Great Britain, and with great success. Turkey red is essentially a madder red with an aluminous basis, but differs from a common madder red by containing oil, and it is the fixing and combining of the oil with the fibre and the colour which constitutes its peculiarity. Divested of details the process of producing Turkey red may be divided into four stages :(1) the oiling of the cloth ; (2) mordanting with a salt of aluminium ; (3) dyeing with madder, or its equivalents garancin or alizarin; and (4) the brightening of the dyed colour. The preparation of the cloth with oil is a process used in no other kind of dyeing ; of its utility there can be no doubt, but all the attempts of chemists to explain the rationale of its action have failed. There are many modifications of the method of applying the oil, but the older and more commonly used process is to mix the oil with a dilute solution of potash or soda ash, so as to diffuse it uniformly through the liquid, forming an emulsion; the oil is not dissolved by the alkalies, nor is it supposed to combine with them, but is simply held in a state of excessively fine mechanical division. A low quality of olive oil is most generally used in Europe, that from Mogador, in the north of Africa, being very suitable. Certain kinds of oil do not answer for Turkey red, only those being suitable which, pro-bably from containing free fatty acids or albuminous matters, readily form a milky emulsion with weak alkaline solutions ; other kinds are, however, in use in some places. The cloth to be dyed is steeped in the oily emulsion, wrung out, and dried in a warm stove ; this process is repeated six or eight times, and the cloth is finally washed in weak alkali to remove from it all the oil not intimately united to the fibre. The result of this treatment, which is the most delicate and important in the Turkey red process, is that the cloth becomes impregnated with a fatty matter, which by the contact of alkalies and heated air has undergone some change from its original state, which is usually called an oxidation, but the nature of which is really unknown. The cloth now possesses a power of attraction for mordants and colouring matters greatly superior to untreated cloth ; and further, its physical condition is changed so that colours upon it are more transparent and more vivid than upon ordinary cotton.
The cloth in this state is ready for mordanting, which is done by passing it through a bath of alum, partly neutralized with carbonate of soda or by chalk, or in a bath of acetate of alumina, the object being to obtain a regular deposition of the aluminous base upon the fibre ; the excess of mordant is carefully washed away from the cloth, which is now ready for dyeing.
The dyeing is accomplished in the ordinary way, by keeping the cloth in continual motion in a vessel containing heated water and the dye stuff, which may he madder, garancin, or artificial alizarin. It is a very general practice to add a quantity of ox-blood to the water used in dyeing Turkey red. What purpose this fulfils is not known; its colouring matter cannot be supposed to be of any use; its albuminous constituents may have some useful action, but this seems very doubtful; probably its addition is quite superfluous, and is retained from older times, when dyeing was less understood than at present. When the dyeing is completed the colour is a full and deep but dull red, which requires brightening. The brightening operations consist in removing brownish matters from the dye by boiling in soap and alkalies. To give a still more brilliant colour, the goods are boiled for several hours in a closed copper boiler with a mixture of salt of tin with the soap used ir the last process of brightening,occasionally under a pressure greater than that of the atmosphere, in order to obtain a temperature some degrees higher than 212' F.
In many processes of Turkey red dyeing, the cloth is treated with decoction of gall-nuts, or with sumach, after the preparation with oil and before the mordanting; this enables it more easily to absorb and fix the aluminous mordant, but it is not essential, and is most generally omitted.
No allusion has been made to a number of excrementitious and other animal matters, which the old dyers used in the oiling process, such as sheep-dung, cow-dung, ox-bile, &c.; they can be dispensed with, and were employed probably from caprice and ignorance.
Barwood red.An imitation of Turkey red is obtained from barwood ; it is much inferior both in beauty and stability to the real colour, but the ease with which it can be dyed, and the less costly nature of the materials employed, enable it to be sold at a much lower price, and for some purposes it is largely used. Bar-wood is one of the red dye-stuffs of which the colouring matter is very slightly soluble in water ; it is used in a state of fine powder. The cotton to be dyed is impregnated with a tin mordant by any of the means known to dyers, and then boiled with the dye-stuff"; the colouring matter as it dissolves is fixed by the mordant, and the process is continued until the required shade is obtained. This wood, and a similar material called camwood, are also employed in woollen dyeing to give brownish reds, and to dye a '' bottom " or foundation for indigo blue colours, by which some economy in indigo is effected, and a peculiar bloom on the blue is produced.
The class of woods represented by Brazil wood, do not yield good reds upon cotton.
The most important of the blue colouring matters is indigo. This may be said indeed to be the most im-portant of all colouring matters, both as regards the large quantity and monetary value of what is produced and sold, and the permanence and solidity of the dyed colours which it yields. The indigo dye is a manufactured article, prepared in the place of growth of the plant wdiich produces it. The indigo plant could itself be used for dyeing, but from 200 to 250 ft> of it would be required to produce the effect of a single pound of the prepared indigo. In England, and many other countries possessing a temperate climate, the species Isatis tinctoria, or woad, has been cultivated, and has been used from time imme-morial for dyeing blue. Its comparative poverty in colour-ing matter has caused it long since to be disused by dyers as a source of colour ; it is, however, employed by them in the preparation of their indigo vats, but rather as a convenient material to induce fermentation than as a dye.
Indigo is distinguished from nearly all other colouring matters by its complete insolubility per se in water and other ordinary solvents. It dissolves to a very slight extent in heated aniline, petroleum, and acetic acid, which upon cooling redeposit it; the only real solvent for it is anhy-drous acetic acid mixed with a little sulphuric acid, from which water precipitates it unchanged, but this solvent is inapplicable in dyeing. But solubility is an essential condition for dyeing, and means have been found to obtain satisfactory solutions of indigo by circuitous methods which involve the temporary destruction of its blue colour and a change in its chemical composition. By various deoxidizing agents, indigo blue can be chauged into a white substance, indigo white, which dissolves with facility in all alkaline liquids, forming a colourless or slightly yellow solution. On exposure to the air or other sources of oxygen, the solution yields the insoluble blue indigo, and permanently dyes any fibre which has been saturated with it.
This is the only case in which such a method of dyeing is applicable, and on that account it possesses much interest. We shall now proceed to describe some of the practical methods in use for indigo dyeing.
Fermentation process.The oldest of these, and one naturally suggested by the method employed in preparing the dye-stuff, is the process of fermentation in contact with lime, or sometimes soda or potash. During this process, gaseous or liquid substances are formed, which have the power of reducing indigo from the blue to the white state, and fitting it for dyeing. This ancient method has not been superseded in England at least, being employed at the present day for nearly all woollen goods dyed with indigo, the consumption of which is greater for woollen than for all other kinds of cloth.
The wood vat.To a course of lectures upon dyeing, recently delivered by Mr Jarmain before the Society of Arts, we are indebted for the substance of the following account of the woad vat used by the Yorkshire dyers. The materials employed are indigo, woad, madder, bran, and lime. For this process as for every other in which it is employed, the indigo must be reduced to the finest possible powder. It is generally ground mixed with water, in closed revolving cast-iron cylinders containing iron rollers or balls, for several days, or until the slime or pulp formed contains no visible particles of the dye-stuff. The proportions of materials employed are :
Lincolnshire woad 5 ewt.
Whtaiten bran 18 lb.
Slaked lime in dry powder 22
The woad is first placed in the dyeing vat nearly filled with water, which is heated to between 140° and 150° F.; after some hours (required to soften the woad),the bran, madder, and indigo are added, and half of the whole quantity of lime. In a few hours, if all is right, signs of commotion produced by fermentation will be visible, the liquid will become greenish, and a blue scum will be visible on the surface; a piece of wool is put in as a test, and if in a short time it becomes dyed blue the process is proceeding well; a little more lime is added, but at intervals, so as not to checkthe progressing fermenta-tion, and, if it should become necessary, the vat is heated up by steam to its original temperature; on the third day the vat should be ready for dyeing. Such a vat as this requires skilful management to control the fermentation; without lime the reduced indigo would not be dissolved; with too much lime the fermentation would be stopped. The woad acts as an easily fermentable matter, and furnishes a portion of blue colour; the bran also no doubt is useful, on account of the ease with which it begins and promotes fermen-tation; the madder is probably of no use at all, its employment being still continued from an old unfounded notion that it gives some of its red colouring matter to the indigo-dyed goods, for the small amount of saccharine matter present in 2J lb of madder cannot be held of any importance in the presence of 5 cwt. of woad.
A woad vat, when ready for dyeing, consists of a certain depth of a tolerably clear solution of white indigo in lime, and a somewhat voluminous semi-solid mass at the bottom, consisting of the bulk of the woad, the excess of the lime, the insoluble part of the madder, and the impurities always present in indigo. To keep the cloth to be dyed from contact with the muddy bottoms an iron hoop, of the internal diameter of the vat, covered with a network of open meshes is lowered into it and secured at a safe distance from the bottom.
The pieces to be dyed, after being well cleansed, are placed in the liquor, and kept in constant movement to insure full access of the colour to all parts. The time required to dye, varying from 20 min-utes to two hours, will depend upon the fineness and weight of the cloth, and upon the depth of colour required; if the goods require it, they are dyed a second time. In moving the pieces about, theymust not be brought above the surface of the liquid, for the oxygen of the air-would restore the dissolved white indigo to its blue insoluble state. When the pieces are found to be sufficiently impreg-nated with the dye, they are withdrawn from the vat ; at the moment of leaving the dyeing liquor they are seen to be of a yellowish colour, which almost instantly changes into a bright green, then darker green, and finally becomes blue through the absorption of oxygen by the white indigo. Loose wool or yarn is dyed by inclosing it in an open and movable network bag.
The vat above described can of course dye only a limited quantity of material, becoming after every operation poorer in indigo; but it is net necessary to re-set a vat. The strength of its contents is kept up by constant additions of indigo, lime, and bran; no more woad is added, the quantity used at first being sufficient for about its own weight of indigo.
Bran and molasses vat.Another kind of indigo dye vat ^ery extensively used ou the Continent, and highly spoken of by practical men, is prepared as follows. A vat 6 feet in diameter and 7 feet deep is filled with water warmed to 130° F.; then 4J lb of ground indigo, 34Tb crystals of soda (or instead 16 lb soda ash) and 671b of bran, and twelve hours afterwards 2 tt> slacked lime, are added; in 24 hours the indigo should commence to be dissolved, and a test strip of stuff plunged in the liquid should be speedily dyed, but some hours longer and the gradual addition of 18 or 20 lb more of lime are required to bringthe liquor into its best condition. In this vat, as in the woad vat, the lime controls the fermentation of the bran, and has to be added with care. With each pound of indigo added to replace what has been removed from the vat during a day's dyeing oJ ft of molasses and \ Tb crystals of soda and 3 or 4 fb lime must be used. By daily replenishing the vat it can be used continually for four or five months ; at the expiration of that time the bottoms must be removed; the supernatant liquor containing indigo in solution may be used instead of water for setting a fresh vat. This vat is said to have quite supplanted the old woad and madder vat, molasses being preferable on the score of cheapness and also of solubility.
The soda not being necessary for the solution of the indigo could be omitted in the setting of the vat, but it is reckoned useful in assist-ing the wool to take the dye; for the wool, however well it be bleached, is said to retain some greasy matters that yield to the soda, which thus enables the indigo to give fuller and faster colours than when lime alone is used.
It is to be observed that the two vats just described are what are distinguished as " warm vats," being made and worked at a tempera-ture considerably above that of the air,a condition held necessary for dyeing wool and some kinds of heavy cotton goods. For ordinary cotton-dyeing the vats are used cold or at the ordinary temperature of the air, and are prepared in quite a different manner.
Copperas and lime vat.A strong copperas and lime vat is com-posed as follows :_
900 gallons of water. 60 fb green copperas 86 lb ground indigo. 80 to 30 tb dry slaked lime.
These materials are well mixed together andrakedupatintervalsfor say 24 hours, when the vat is ready for use. The lime decomposes the salt, liberating ferrous oxide, which acts upon the indigo, con-verting it into white indigo, which dissolves in the lime water. In large establishments for dyeing calico blue, it is usual to have a series of such vats in a row ; the pieces to be dyed are tightly stretched on a frame and dipped in the liquid for from seven to ten minutes, after which they are believed to be as fully saturated as possible ; the frames are next raised into the air, and in a few minutes the blue colour becomes developed; the same process is then repeated until the required depth of colour is obtained. By printing certain resisting compositions on the cloth previous to the dipping, white figures can be obtained upon a blue ground, producing what is known as the navy-blue style of print, formerly much worn by the low-er classes in England. By combining suitable mordants with the resisting composition, not only white, but orange, yellow, and green coloured figures can be obtained upon the blue ground; but the production of these is rather a branch of calico printing than of dyeing proper.
Although this kind of vat is most generally used for the lighter qualities of calicoes, it can also be applied to such woollen goods as nierinoes, which are not very closely woven, and also to silks.
Hydrosulphite of soda rat.In 1871 Schiitzenberger and Lalande introduced a new reducing agent applicable to indigo dyeing, the so-called hydrosulphite of soda, obtained by acting upon acid sulphite of soda with metallic zinc. It possesses the most energetic deoxidizing powers, and in the presence of alkalies almost immedi-ately reduces and dissolves indigo. It has been applied both in dye-ing and in printing indigo colours, but cannot be said to have succeeded in displacing the older kinds of vats, having the disad-vantage of costing much more without producing any apparent improvement in the colour yielded.
By preparing a very strong indigo vat, and thickening the fluid with gum, it is possible to print indigo blue colours in designs, but the many difficulties attending the process have very much restricted its application.
The colour yielded by indigo, though far from brilliant, is ex-traordinarily permanent, and is much used for articles intended to withstand much wear and rough usage, and also as a basis for the best quality of black upon fine woollen cloth.
Sulphate of indigo.When indigo is acted upon by concentrated sulphuric acid it forms a solution of the so-called sulphate or extract of indigo, which, though possessing an intensely bine colour, cannot by any means be made to furnish the original dye. This preparation of indigo is applied only in wool and silk dyeing ; itgives blues which are tolerably bright, but possess none of the stability of those obtained from real indigo. For vegetable fibre it has no affinity whatever either with or without mordants.
Prussian blue.This, perhaps the earliest of artificial dye-stuffs, was accidentally discovered in 1710, though not used in dyeing for some time afterwards. The simplest method of employingit consists in first impregnating the material to be dyed with peroxide of iron, and then passing it into a solution of yellow prussiate of potash acidified slightly with sulphuric acid. Prussian blue upon silks is thus dyed. The most convenient way of obtaining a deposit of the oxide of iron consists in soaking the silk in a somewhat strong solution of the ordinary dyers' nitrate of iron; in the course of two or three hours a certain quantity of the oxide is found to be intimately combined with the silk ; the excess of nitrate is then washed away and the silk worked in the acidified prussiate bath, when it imme-diately assumes a light azure shade; by repeating the treatment several times any depth of colour may be obtained.
Calico can be dyed in the same way, but both for that and for silk it is usual to add to the iron solution a small quantity of salt of tin, which is useful in giving a purplish tone to the blue and preventing the production of a disagreeable greenish tinge.
A deep colour cannot in this way be satisfactorily given to woollen, for which a treatment is adopted depending upon a decomposi-tion of the prussiate by means of heat and acids. For dyeing say 110 lb of merino the following proportions and methods may be used. Dissolve 9 lb of yellow prussiate of potash in hot water, and add the solution to the required quantity of water ; then add 14 lb sulphuric acid, 6 lb sal-ammoniac, and about 6 oz. of crystals of protochloride of tin; the merino is placed in the mixture, and the temperature of the dye-bath gradually raised to the boiling point in rive hours. The blue gradually formed on the cloth requires brightening in a fresh bath consisting of alum, persalt of tin, and cream of tartar, heated to nearly the boiling point. Red prussiate of potash is used in nearly the same way to dye dark Prussian blues upon wool, but as it is more easily decomposed than the yellow prussiate a weaker acid-bath suffices. These blues are frequently finished off with logwood to give them a deeper tone.
Prussian blues can also be obtained on such woollen goods as merinoes, by a process of padding, and the use of a colour nearly identical with the so-called French or royal blue used by calico printers. Amixture is prepared as follows. Haifa poundof wheaten starch is boiled with about half a gallon of water; in the thin paste thus made 13 oz. of powdered yellow prussiate are dissolved, and afterwards 6 oz. of tartaric acid ; when the mixture is quite eold 1 lb of prussiate of tin in paste is added, 1J oz. oxalic acid, and 3 oz. sulphuric acid; the whole is well mixed and strained. The woollens to be treated are first " prepared," as it is called, by impregnating them uniformly with oxide of tin, and then the above thickened mixture is applied by means of rollers, so that it shall be evenly and smoothly spread over the whole stuff; the cloth is then dried and exposed to the action of steam, which causes the acids to react upon tte prussiates, and from a nearly colourless mixture develops an intense blue, which is found to be permanently fixed in the fibre.
Aniline blues.There are several artificial blue dyes made from aniline and similar bodies, which yield very brilliant colours on wool and silk. They can be easily applied, the goods simply requiring to be worked in their aqueous solution until they have acquired a sufficiently dark tinge. An artificial dye called Nichol-son's blue is differently applied; it is dissolved in an alkaline liquid, and forms then a colourless or nearly colourless solution, with which the goods to be dyed are impregnated; they are then passed into dilute acids, which develop the blue colour.
Litmus and logwood blues.The other substances which have been used for blue colours, such, for example, as litmus, are of little importance, and are now nearly unknown to the practical dyer. A blue can be obtained from logwood which has some resemblance to indigo blue upon wool, but it is of a very low character both as to stability and shade, and is hardly ever employed by respectable dyers.
Yellow textiles, being less pleasing to the eye, and more readily soiled, are not nearly so much in use as those dyed with the two simple colours blue and red. The chief yellow dyes, besides fustic, are quercitron bark or its concentrated extract flavine, Avignon or Persian berries, and the now almost disused indigenous product, weld. The general mordant for these is tin, sometimes with addition of alum. One or two illustrations will suffice to show the methods of using them.
Fustic-yellow.Fustic is probably the most generally employed yellow dye-stuff for wool; it gives yellows inclined to orange. For light shades it is not necessary to mordant the wool; it is simply well cleansed, and then heated with fustic decoction and some cream of tartar. For darker shades the wool is boiled with solution of tin and tartar, washed, and then worked in the decoction of fustic.
Picric acid yellow.Picric acid, one of the artificial colouring matters, gives pure though not deep yellow shades upon silk and wool without the aid of a mordant, the cleansed material being dyed by working it in a warm solution of the acid.
Chromate of lead yellow.The yellow most commonly employed for cotton goods is obtained by the use of salts of lead and bichromate of potash. The method of obtaining this colour differs somewhat from any previously described. The cotton, having been properly bleached, is impregnated with a salt of lead, usually by employing a solution of the acetate or sub-acetate of lead. The goods are next passed into a milk of lime solution, to wiiich it is pru-dent to add some acetate of lead, in order to prevent the lime from dissolving the oxide of lead at first precipitated; the result of the lime treatment is that oxide of lead is evenly fixed upon the cotton, the excess of lime and lead is then well washed away, and the goods are passed into a solution of bichromate of potash, where they quickly acquire a bright and deep yellow colour, owing to the formation of the well-known pigment chrome yellow. To facilitate the combination, the bichromate of potash is mixed with as much sulphuric acid as suffices to liberate the whole of its chromium as chromic acid. The yellow-dyed goods require no further treatment than a good washing, the colour being quite fast. This yellow is, however, in very little demand, and in ninety-nine cases out of a hundred it is immediately converted into an orange, by passing it through boiling lime-water, which produces the basic chromate known as chrome orange, which has alway been in demand for many articles of wear.
The so-called simple coloursred, blue, and yellow having now been dealt with, it remains to treat of their combinations, and this may be done briefly, the processes employed being for the most part similar to those already described. The compound shades in Chevreul's chromatic nomenclature amount to nearly 15,000, and it is very pro-bable that fully that number are produced by the dyers of the present day. For practical treatment, however, the compound colours can be reduced to comparatively few classes. Mixing the simple colours one and one we obtain three compound colours,blue and yellow give green, blue and red give purple, yellow and red give orange ; while there may be a normal green, purple, and orange, it is evident that all the varieties of these several colours will depend upon the proportions of their constituents. If the three simple colours be mixed together, say in equal pro-portions, we may get a normal brown, or even a black ; but if in unequal proportions, an immense number of shades, varying from the imagined normal brown to grey and drab, are produced. Although in many cases compound shades are produced by means of two or more simple colours, there are many natural as well as artificial dye stuffs which yield them ready formed, and frequently purer than they can be otherwise obtained. Most of these will be found mentioned in the following brief notice of practical processes in use.
Lo-kao or Chinese green.Until about the middle of the present century there was not an instance known of any green on textiles which was not composed of the two separate colours blue and yellow. About that time some green-dyed cottons, imported into France from China, attracted the attention of chemists, who were surprised that they could not separate the green into blue and yellow constituents. Inquiries showed that the Chinese employed a green colouring matter called Lo-kao, until then unknown in Europe. It was a costly dye-stuff, selling in China for its weight of silver. Some quantity of it was imported and used in silk-dyeing by the French; it was not, however, found altogether satisfactory, and has at length been quite abandoned for the aniline greens, which are in every respect preferable.
Aniline green.There are two or three kinds of artificial green dyes in use, of which that known as methyl-aniline green, applied in silk dyeing, is most in request. The so-called iodine green ha3 also been somewhat extensively employed for all kinds of fabrics.
These artificial and unstable materials are the only dye-stuffs for green possessed by the dyer, who is compelled to produce the colour by means of blue and yellow elements. The arsenical mineral green and the oxide of chromium green may be just men-tioned as of extremely limited employ. 'I he blues used in dyeing green are indigo, Prussian blue, and the sulphate of indigo. The yellows are afforded by Persian berries, quercitron, fustic, or the yellow chromate of lead. The processes employed consist, for the most part, in the separate application of the blue and yellow: for example, in dyeing a fast green upon wool from indigo and any of the yellow dye-stuffs, the blue is first produced as previously described, and the proper mordant for the yellow is then applied to the cloth, which is afterwards placed in the yellow colouring matter; the two colours are so intimately mixed as to be indistinguishable even by high magnifying powers. It may be observed that the reception of the blue does not to any perceptible extent diminish the power of the cloth to combine with the yellow.
Prussiate green.Prussian blue is employed as a basis in the same manner, only not being capable of resisting chemical agents so well as indigo blue, it demands more care. The greens with Prussian blue bases are more lively than those made with indigo, but are not so fast. Sulphate of indigo is even less stable than Prussian blue. It is, however, cheap and easy of application, and gives rich colours. The greens made with chromate of lead are for the most part con-fined to cotton goods, and are not in much demand.
For cotton the chief orange-dye is the chromate of lead compound already described. For other materials the orange colours employed are nearly always composed of some of the red and yellow dyes mentioned in the preceding pages, such, for instance, as cochineal and fustic, which are applied in one hath, the same mordant serving for both.
Arnotto orange.A warm solution of arnotto in weak alkalies is used without mordant to impart to silk an agreeable orange shade. Its colour is generally considered too yellow, but may be made redder by treatment with weak acids, or by previously giving the silk a light red foundation.
Picric acid orange.Another orange on silk can be dyed by strperimposing on a light pink a yellow obtained from picric acid.
Nitric acid orange. Silk can also be permanently stained of a yellowish orange by means of moderately strong nitric acid, which must, however, be applied with great care, since a more than momen-tary contact would be very injurious to the strength of the fibre. This method of dyeing silk was formerly much used for handker-chiefs ; by protecting certain parts from the acid with melted wax or similar resists, white designs were produced upon an orange ground.
The purple colours may be held to include all shades produced by an admixture of red and blue, such for example as lilac, violet, mauve, &c., and are of immense variety.
Aniline purples.Since their discovery aniline colours have been almost exclusively employed for dyeing silk and wool purple, yielding as they do shades which for lustre and purity surpass any obtainable from the older colouring matters, and possessing also a fair amount of stability. An aqueous solution of the dye without mordant is all that is required, and the goods when dyed need very little subsequent treatment. The aniline purples, violets, and mauves do not dye upon cotton without previous mordanting, and even then are so loose and unstable that they are only fitted for use where great fixity is not demanded, as for linings of clothing, &c. The most general mordant for the aniline purple colours on cotton consists of a tannate of tin obtained by first steeping the cotton in a solution of tannic acid, or in decoction of gall-nuts, sumach, or myrobalans, all of which contain tannic acid; after a few hours' contact a considerable quantity of tannic acid has become firmly attached to the cotton, and the goods, being now treated successively with stannate of soda and dilute sulphuric acid or in other ways, acquire a certain proportion of oxide of tin, and are prepared to receive the colours.
Madder purple.But the purple colour par excellence upon cotton is obtained from madder or alizarin, the mordant being oxide of iron or a sub-salt of iron deposited on the fibre by treatment with the commercial pyroliguite of iron, commonly called iron liquor. This purple is remarkable for great permanency. It is very largely used in combination with black and white in the best kind of printed calicoes.
Archil purple.Archil and cudbear are sources of purple colours on wool and silk. The shades produced are rich and beautiful; they are not, however, very permanent, and have been nearly superseded by the aniline colours. Of the few instances that can be cited of stuffs dyed purple by the direct union of red and blue colouring matters, the violet or purple woollen cloth used for ecclesi-astical purposes is an example. The indigo colour is first fixed and cleansed, and then the cloth is dyed with cochineal and tin mordants in the way already described for dyeing scarlet. The purple thus obtained is a fast colour, but is very costly, and on that account is not much worked.
The common shades of purple, violet, lilac, &c, upon wool are obtained from logwood with a mordant of alum and tartar; the red woods are sometimes employed in conjunction with logwood for these colours, which are " topped " with archil to give them more brilliancy.
The extensive range of colours, comprising all the shades of brown, bronze, chocolate, nut, wood, drab, and grey, which may be considered as compounded of the three elementary colours, some one of the three predominating, can only be briefly treated of in this article. Most of them are actually produced by the use of dye-stuffs yielding the three simple colours ; but there are colour-ing matters like catechu, which themselves yield brown colours, and others, such as logwood, wdiich may be held to contain two or more of the simple colours, the blue predominating. A few illustrations will show how these triply compounded colours are produced by the dyer.
Bronze brown on wool.The wool is mordanted with alum and tartar in the usual way, and is then dyed in a mixture of fustic and madder or other equivalent red and yellow dye-stuffs; for fast colours a blue part can be communicated to it by the indigo vat. For a lower class of colours no indigo is used, but instead, a mixture of yellow wood (fustic or quercitron) with madder for the red, and logwood for the blue part; or again, the sulphate of indigo may be employed for the blue.
Tan brown.According to Mr Jarmain, the wool is mordanted by boiling it for an hour with one per cent, of its weight of bichromate of potash ; it is then washed, and transferred to the dyeing vessel, with the following percentages of its weight of materials : madder, 3'2; fustic, 4'8; camwood, 2; barwood, 175; sumach, 2'1 ; with these materials it is boiled for two hours.
Dark drab.From the same authority we take the following as the weights required to dye 100 lb wool, previously mordanted with 1 lb of bichromate of potash:camwood, 64 lb; sumach, 2 lb; madder, 2 J lb ; fustic, 41b ; logwood, 2 J lb ; boil for one hour and a half, and afterwards, to darken the colour, pass into water containing 1 lb of sulphate of iron.
Black, from a dyer's point of view, is compounded of the three simple colours, red, yellow, and blue, in a state of concentration; but in reality the blue predominates in all good black colours, and gives them their density and at the same time their lustre. What is called a dead black, crape black, or jet black, is the nearest approach to a neutral black, but even this would be brownish if the blue did not predominate. It is often extremely difficult to obtain a black dye to suit a particular market. Of ten pieces ap-pearing equally black to the uninitiated, an expert would, perhaps, pronouace one to be sooty, another purple, another red, another brown, another green, and so on.
We should have to go back some years in the history of dyeing, to find a time when black was actually dyed with the three elementary colours. In some processes blue from indigo was first applied, and then, upon an alum mordant, red and yellow from madder and weld respectively; such a colour was unexceptionable for stability, but its great cost caused it to be disused.
At the present day, logwood is the chief dye-stuff for blacks upon wool or cotton, and gall-nuts and other astringents for silks. Ani-line black, on account of obstacles to its application, cannot be said to have yet established itself in dyeing proper, though it is much and highly valued in calico printing.
Black dye upon silk.Silk easily takes a black by treatment first with decoction of gall-nuts, and subsequently with a salt of iron. For blue blacks the silk is usually first dyed with Prussian blue, and then with gall-nut black. Extract of chestnut-wood with an iron mordant gives a good black. In modern black silk dyeing, materials are heaped upon the fibre which are not necessary to its colour, but which increase its weight in an extraordinary manner, so as not only to compensate for the loss of 25 per cent, of natural gum in the silk, but even, in some cases, to double or treble the original weight. The silk is, of course, much injured by the ac-cumulation of foreign matters upon it, the fibre becoming harsh and brittle, and soon showing the effects of wear. The chief sub-stances used for weighting are lead salts, catechu, iron, and galls, with soap or fatty matter, to soften in some degree the harshness these occasion.
Black upon wool. Upon woollen cloth of fine quality, the black is dyed upon a basis of indigo blue, and, from the use of woad for this colour, such blacks are in England called " woaded blacks." The first process, therefore, in producing the best black is to dye the wool in the indigo vat of a tolerably deep shade of blue, and afterwards boil it in a mixture of logwood and sumach, treating it with sulphate of iron ; the latter process being two or three times repeated, a very perfect and durable black is obtained, provided the indigo basis is sufficiently deep, and only a minimum quantity of logwood has been employed, say about one-fourth the weight of the sumach.
Common black.Common blacks upon wool have noindigo in their composition, but are dyed chiefly with logwood and iron salts; the wool and logwood are heated together for some time, and then sul-phate of iron is added to the dye-bath. In other blacks of somewhat better quality, the woollen is boiled for some time with solution of iron, copper, and aluminium salts, together with tartar, and when the mordanting oxides have been fixed, the colour is dyed up in logwood. The bichromate of potash mordant can also be used for the black dye, and the cloth can be "bottomed " with camwood or barwood; it is then dyed up with logwood, to which fustic or sumach may be added.
Black upon cotton.Almost the only ordinary black in cotton dyeing is obtained from logwood with iron mordant; sumach is sometimes used, and very rarely the black is dyed upon an indigo blue basis by means of sumach or galls and iron. As before stated, aniline black has not yet been practically applied in dyeing cotton. A common method is to first heat the goods for some hours with decoction of sumach, wash mordant in sulphate of iron, and then dye in logwood; another method consists in fixing an iron basis upon the cotton by the method given above (page 573), and dyeing in logwood, along with a portion of sumach or fustic, according to the shade required.
Velvet dyeing.The most important branch of black dyeing upon cotton goods, is that employed for cotton velvets and vel-veteens, in which it is desired to produce a rich lustrous effect; the process is long, tedious, and uncertain, consisting of successive applications of sumach, sulphate or acetate of iron, sulphate of copper, logwood, and fustic,the end chiefly aimed at being the production of a black with blush or violet bloom. The Manchester dyers formerly held a monopoly of this blue-black upon velvet, as it is called, but of late years the German dyers have shown themselves very formidable competitors in dyeing this class of goods.
THEORY OF DYEING.
When the great variety of processes employed in dyeing is taken into consideration, it is apparent that there must be some difficulty in constructing a general theory which shall be applicable to every case.
The earlier writers who endeavoured to generalize the principles of the art considered that the particles of colour were mechanically deposited in the pores of the fibre. The use of chemical substances in dyeing was held necessary only to dilate the pores for the admission of the particles, to prepare the particles for entrance into the pores, or to close up the pores after the colouring particles had entered. Mordants were held to be necessary because they formed cavities in the fibre adapted by their size and shape to receive and retain different kinds of coloured particles. About the middle of the last century Bergmann, observing the dyeing of wool by sulphate of indigo, considered that what took place was a purely chemical action, and that the matter of the wool entered into chemical combination with the dye-stuff, changing it from a soluble into an insoluble substance, and showing therein the power of chemical affinity. From this time the mechanical or physical theory of dyeing was supplanted by a chemical theory, in which all the observed facts were explained by the assumption that chemical forces operated between the fibre and the mordant, or the fibre and the colouring matter. A closer considera-tion by a later generation of chemists of all the phenomena of dyeing and of the nature of the materials employed did not tend to support this theory. About 1840 Dumas, the celebrated French chemist, and Crum of Thornlicbank, a skilful chemist and a practical dyer, formally disputed the existence of a chemical action in dyeing, and referred the phenomena to physical causes of attraction on the part of the fibre. Crum confined himself to the single case of the dyeing of cotton, and expressed himself convinced that it was owing either to surface contact of the dye stuff with the cotton or to its entrance into the hollow tubes of the same, the colours produced in the first case not being so stable as in the other, as far as resisting friction went. The power which cotton fibre evidently possesses of appropriating oxides from solutions, as well as colouring matters, such as indigo, was viewed by Crum as a case of surface attraction, similar to the power residing in charcoal of abstracting oxides and colouring matters from solutions, and he declared there was no such thing as a chemical combination between the cellulose of the cotton fibre and any of the chemical sub-stances or dye materials. To controvert this statement is difficult, for, though the forces at work seem to be chemical forces, the products cannot be proved to be definite chemical compounds. On the other hand, the forces of catalysis, surface attraction, and powers of porous substances which Crum substitutes for the chemical forces of the older theories of dyeing, may be said to be merely names, without definite meaning, for indicating the existence of a class of phenomena not at all understood even at the present day. Dumas views the questions more broadly, and simply declines to accept as chemical phenomena actions which do not produce real chemical compounds. He considers that dyeing is more probably owing to a physical property of fibres by which they are enabled to attract and retain coloured bodies, much in the same way that animal charcoal does, and simply because the nature of the powers exercised by charcoal are not accepted as chemical, and no one knows what they are, dyeing cannot be considered as an effect of chemical attraction or affinity. He admits, however, that there are some powers at work different from that possessed by charcoal. How is it, he asks, that wool takes up the scarlet dye so well under conditions where silk and cotton are barely tinged with colour 1 How is it that wool unites with the black precipitate formed with tannin and iron salts, while silk under the same circumstances is so difficult to dye 1 He asks, finally, how it is that certain colours can be fixed better on some fibres than others ; and wdiether it is not by some special action, not correctly called affinity, but which at auy rate is an important force, or the resultant of several forces, that this is affected. But, he continues, to confound chemical affinity, properly so called, with the phenomena of dyeing is to confound two very different things. When silk unites with Prussian blue, or wool with indigo, the action is quite distinct from what takes place when sulphur combines with lead. But, on the other hand, again fibres are not to be looked upon as acting simply the part of a filter in retaining colours.
Chevreul, at a later date, insists that in the present state of our knowledge the phenomena of dyeing can be explained only upon chemical principles. He admits that colour may be and in practice is frequently deposited upon the external parts of fibres, but there are numerous cases in which a soluble salt is decomposed by fibrous matters, as when silk is steeped in persulphate of iron ; and he cannot consider as anything else than chemical affinity that power which enables a solid body to decompose a solution of elements, themselves united by chemical affinity, and which without the contact of the solid body would have remained in per-fect union. Many other chemists, physicists, and micro-scopists have occupied themselves upon this vexed question, but without evolving any generally acceptable theory of dyeing. The balance of opinion may be said to be in favour of the supposition that as far as regards the animal fibres, wool and silk, there are many cases of dyeing which can only be regarded as effected by chemical powers ; with respect to the vegetable materials cotton and linen, the evidence is less certain, and we must wait for further research and investigation to settle the disputed question.
Books of Reference.Of the numerous works upon dyeing it may be sufficient to mention Bancroft's Philosophy of Fermement Colours (2d ed. 1813) ; Berthollet's Eléments de la Teinture, and lire's translation of the same into English (1811) ; Persoz's 'Traité de l'impression des Tissus (1S46),a most complete and accurate work for its date ; O'Neill's Chemistry of Calico Printing and Dyeing (1860), and Dictionary of Dyeing (1862) ; Napier's Manual of Dyeing (3d ed. 1875) ; Schiitzenberger's Traité des Matières Colorantes (1867) ; Crookes's Dyeing and Calico Printing (1874); and Crace-Calvert's Dyeing and Calico Printing (1875). Of periodicals specially devoted to the application of colouring matters to textiles there is only one in Great Britain, The Textile Colourist ; Germany has the Färber-Zeitung and the Muster-Zeitung ; in France there are the Moniteur de la Teinture and Le Teinturier pratique. Original articles upon the subject occasionally appear in the chemical journals, and especially in the Bulletins of the Industrial Societies of Mulhouse and Rouen. (C. O'N.)