Coal-tar dye

“ The fast or fugitive character of a color is an inherent property of the coloring matter used, and depends mainly, if not entirely, upon its chemical constitution. In order to improve the fastness of coal-tar colors we should examine thoroughly the characteristic of every coloring matter, then choose the fastest and reject the rest, or only employ them when they are perfectly admissible. Such a process of selecting the fittest has gone on in the past with reference to the dye-woods, and such is the sifting process now at work among the coal-tar colors. ”

“ Coal tar dyes have come to stay, vegetable dyes for the most part have gone and will not return, and there is no sadness in the word. It is rather for us to rise to the challenge that has come, to recognize our greater heritage, and by pains, patience and intelligence in our work to ply the art worthily.
COLOR MIXING
The following general principles of color mixing apply to dyeing, both when colors are mixed in a dye-bath and when they are dyed one color over another:
Red is grayed by small amounts of yellow and blue or by any color containing both of these, as green, brown or gray. ”

“ Another opinion is that the fibres have pores, which, when expanded by heat or chemical agents, admit particles of colouring matter. However this may be, it is certain that different materials ‘take’ dyes in different proportions; thus, silk and wool take the coal-tar dyes in the most perfect manner, but cotton requires the intervention of a most powerful mineral or animal mordant. Wool takes the colouring matters of most dye-stuff so well that the deepest tints can readily be produced. ”

“ There would be no need to grow apprehensive concerning our coal-tar dye industry and the manufacture of other products dependent upon materials derived from coal. The British dye industry is in its infancy. At the moment its benzol requirements are modest, being approximately 4,000,000 gallons a year. But it is an industry which, given full opportunity, promises to thrive and to expand amazingly, and so one may safely anticipate that its benzol needs will advance by leaps and bounds. ”

“ Remove the cloth from the solution, wash in boiling water, and dry between pieces of filter paper. A bright red indicates coal tar dye. If the coloring matter is entirely from fruit, the woolen cloth will be either uncolored or will have a faint pink or brown color which is changed to green or yellow by ammonia and is not restored by washing. ”

“ They are all fugitive, and are now of little or no importance to the dyer. The coal-tar colours of this class, on the other hand, are extremely numerous. The developed dyes are formed in situ upon the fibre by the successive application of two or more substances. They include aniline black, a permanent black produced by the oxidation of aniline, and the ice colours, which are azo dyes derived from certain coal-tar products containing nitrogen.
The mordant dyes form one of the most important classes of colouring matters, for they include not only most of the vegetable dye-stuffs, e.g. ”

“ While the shades are somewhat faster to light on wool than they are on cotton, they are no faster to soaping and in some cases not so fast. What may be the function of the salt, or other such added substance, is not very clear, probably it plays the same part as to similar bodies in dyeing the basic dye-stuffs. The dye-stuffs which are referred to above are all derived from coal-tar, and in the recipes which follow many examples of their use will be found. ”

“ We are too prone to compare the ordinary home dyeing of today or the cheaper commercial dyeing with the good pieces that have been preserved from the past. When in justice the comparison is made of the best with the best, the coal tar dyes not only do not suffer but they really gain. ”

“ At the present time it may truly be said that the dyer is furnished with quite an embarrassing number of coal-tar dyestuffs which are capable of producing every variety of colour possessing the most diverse properties. Many of the colours produced are fugitive, but a considerable number are permanent and withstand various influences, so that the general result for some years has been the gradual displacement of the older natural dyestuffs by the newer coal-tar colours. ”

“ By a similar process, using a dye-bath containing the aniline salt and oxidizing mixture, cotton fibre is easily dyed. The black cannot be used for silk or wool, as the oxidizing materials attack these fibres, but for cotton dyeing and calico printing this colouring-matter has come seriously into competition with the black dyes obtained from logwood and madder. The use of aniline for this purpose, first rendered practicable by Lightfoot, is among the most important of the many wonderful applications of coal-tar products in the tinctorial industry. ”

“ In the making of illuminating gas, itself a finished chemical product of the century, a vast amount of once wasted products, especially coal tar, are now extensively used; and from coal tar and the residuum of petroleum oils, now come those splendid aniline dyes which have produced such a revolution in the world of colours. The saturation of sand by a dye and its application to fabrics by an air blast ”

“ Since, however, they yield fast colors with other useful mordants, and upon other fibers than wool, these alizarin colors prove of the greatest value to the dyer of textile fabrics generally. Let us not forget the fact, then, that it is among the "mordant dyes," the very class to which belong most of the natural coloring matters, that we find our fastest coal tar dyes. ”

“ The artificial blues derived from coal tar are very numerous, and representatives of all classes, direct, basic, acid and mordant of dye-stuffs may be found among them. The direct blue dyes do not work very well on wool. They are apt to dye very red, and somewhat dull shades, which are, however, fairly fast to washing and light. The basic blue dyes are fairly numerous, and may be used to dye from pale sky to deep navy tints. They are apt to work somewhat unevenly on to wool, owing to their great affinity for the fibre. ”

“ Now I will mention a process for dyeing felt a deep dead black with a coal-tar black dye which alone would not give a deep pure black, but one with a bluish-purple shade. To neutralise this purple effect, a small quantity of a yellow dyestuff and a trifle of indigotin are added. A deep black is thus produced, faster to light than logwood black it is stated, and one that goes on the fibre with the greatest ease. But I have referred to the use of small quantities of differently coloured dyes for the purpose of neutralising or destroying certain shades in the predominating colour. ”

“ The coal-tar or aniline blues are not offered to the general public as laundry blues, but laundry proprietors have them frequently brought under their notice, chiefly in the form of solutions, usually 1 to 1 1/2 per cent strong. These dyes are strong bluing materials, and, being in the form of solution, are not liable to speck the clothes. Naturally their properties depend upon the particular dye used; some are fast to acids and alkalies, others are fast to one but not to another; some will not stand ironing, while others again are not affected by the operation ”

“ Dyeing. When a fabric or fiber is impregnated with a uniform color over its whole surface, it is said to be “simply dyed.” On the other hand, if distinct patterns or designs in one or more colors have been impressed upon a fabric, it is called printing.
Vegetable dyes were formerly used, but since the coal tar dyes have been discovered the latter are used entirely. Over fourteen thousand colors have been produced from coal tar. Different fibers and fabrics attract dyestuffs with varying degrees of force. Wool and silk attract better than cotton and linen. ”

“ The important vegetable dye catechu (q.v.) is used in dyeing cotton and wool brown. On wool, catechu yields khaki browns in single bath by using copper sulphate as the mordant. On silk, it is largely employed for weighting purposes in the process of dyeing black. Although dyewoods are still much employed, they are being steadily replaced by coal-tar colours. The vat dyes are insoluble in water, but yield reduction products which are soluble in aqueous alkali, and can be readily reoxidized to the dye-stuff. ”

“ There is a widely-spread idea that these colours are fugitive—that they rub off, that they fade on exposure to light, that they wash out, and, in short, that they are in every way inferior to the old wood or vegetable dyes. These charges are unfounded. One of the best refutations is, that two of the oldest and fastest of natural colouring-matters, viz. alizarin and indigo, are coal-tar products. There are some coal-tar dyes which are not fast to light, and [Pg 199] there are many vegetable dyes which are equally fugitive. ”

“ Moreover, all the earlier coal tar dyes—mauve, magenta, Nicholson blue, etc., belonged to a class which, even up to the present time, has only furnished us with fugitive colors. They were indeed prepared from aniline, and it appears to me that the defects of these early aniline colors, as well as their designation, have been handed down to their successors without due discrimination, so that in the popular mind the term "aniline color" has become, as a matter of habit, synonymous with "fugitive color." ”

“ By the introduction of dye-stuffs derived from coal tar the cloth is now dyed after being woven, care being taken to choose those which will dye the two fibres equally well when self-shades are wanted, or those which will dye one fibre better than the other, and thus allow a woven piece of gloria to be dyed of two different colours. As most dyers know, the most brilliant effects are obtained when the finished woven piece can be dyed. ”

“ While such colouring agents as caramel, turmeric, litmus, saffron, beet-juice, indigo, and some of the coal-tar dyes may be considered comparatively harmless, there can be no question in regard to the very objectionable character of certain other pigments which are sometimes employed: these are mainly inorganic, and include plumbic chromate, salts of copper and arsenic, zinc-white, barium sulphate and Prussian blue. ”

“ No permanent effect can be obtained by merely mixing-in coal-tar dyes at random. In addition to certain organic dyestuffs, artificially prepared mineral colours and colour lakes—artificial preparations of an organic dyestuff with an inorganic substratum—are also used for improving. ”

“ Coal-tar dyes are not much used for the production of blacks, as they do not give such a satisfactory result as logwood with an iron mordant. In the dyeing of blacks the preliminary operation of souring is always omitted and that of sumaching sometimes, but if much tan has been removed it will be found necessary to use sumach, although cutch may be advantageously and cheaply substituted. ”

“ Coloring matter used may be coal-tar dyes or pigments such as bone black, carbon black, and iron oxides. Pigments are usually more satisfactory, although dyes are sometimes preferred in articles for insulation.
A lubricant is added to the molding mixture to overcome the tendency to stick in the mold. ”

“ The total number of coal-tar products runs into the thousands, and is constantly being increased by fresh discoveries.
In Germany, just before the war, the industries engaged in making these products (no longer by-products, but far more important than coke and gas) were capitalized at $750,000,000. One firm made no less than 1,800 coal-tar dyes, besides 120 pharmaceutical and photographic preparations. ”

“ If there are natural colouring-matters which are fast and which are æsthetically orthodox, these are rivalled by tar-products which fulfil the same conditions. Such dyes as aniline black, alizarin blue, anthracene brown, tartrazine, some of the azo-reds and naphthol green resist the influence of light as well as, if not better than, any natural colouring-matter. The artificial yellow dyes are as a whole faster than the natural yellows. There are at the present time some three hundred coal-tar colouring-matters made, and about one-tenth of that number of natural dyes are in use. ”

“ But science is progressive, fields of investigation other than aniline have been opened up, so that now, although a large number of fugitive dyes are still manufactured from coal tar, there are others, as we have seen, which are as fast and permanent as we have ever had from natural sources. ”

“ Since the year 1856, in which the first coal-tar colour, mauve, was discovered, the art of dyeing has made enormous advances, mainly in consequence of the continued introduction of coal-tar colours having the most varied properties and suitable for nearly every requirement. ”

“ If we now turn to examine the colors given by these artificial "mordant dyes" on silk, we notice, also, a good series of fast colors similar to those which they give on wool; and even on cotton we see many fast colors, of which we have no representatives among the dyewoods.
If we were not prepared to find so few really fast natural dyes, surely we cannot but be surprised to find what a considerable number of fast dyes are to be met with among the coal tar coloring matters requiring the aid of mordants. ”

“ When we examine the results of actual exposure experiments, such as are here shown on these four diagram sheets, surely we have no hesitation in declaring how utterly false is the popular opinion that all coal tar colors are fugitive to light, while the good old-fashioned natural dyes are all fast. ”