572 DYEING Ancient Practice of Painting, is preserved in the convent of St Salvatore at Bologna, and is said not to be of later dute than the middle of the 15th century that is, about 100 years anterior to the date of Rosetti s work. In this manuscript, in addition to the materials enumerated by Alcherius, mention is made of woad and methods of making itidigo from it ; of indigo imported from India, called lagadon 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 yrana 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 to replace the respective sulphates was of more importance ) 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 185S com menced the discovery and application of a series of artificial colouring matters, which 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 m. ddle 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 shade 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 - POINTING (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 employed the fibre to be dyed and the colouring matter and 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