Page:The New International Encyclopædia 1st ed. v. 06.djvu/641

* DYEA. 559 DYEING. tion; its permanent residents number 261 (cen- sus of 1900J. DYEING (OF. diieit, to dye, AS. deagian, from deag, color; connected with AS. dCaic, dew). The art by which various substiinces, especially textile fibres, are impregnated with coloring matters with sullicient tenacity to resist the action of water or ordinary wear. HisiORT. The art of dyeing was known to the ancients, and it is mentioned in the Bible that Jacob gave his favorite son Joseph a coat of many colors, and iloses tells how the skins of the ram and the badger used for the Tabernacle were dyed red. The purple of the Tyrians was known at an early date: the King adopted it as one of his principal ornaments, and it has since continued a badge of royalty. Accord- ing to Pliny, this purple color was derived from certain shellfish found along the coast of Phoe- nicia, but the method of its preparation was lost. Pliny is also the authority for the state- ment that "methods of dyeing black, yellow, and green were brought into Greece from India on the return of Alexander the Great. Toward the close of the Middle Ages the art of dyeing was greatly developed in northern Italy, especially in Florence, where the dyestuff archil (q.v.) was discovered about 1300." The early voyagers to America brought back with them new and valu- able dyestuffs, such as cochineal, log^vood, and quercitron. Subsequently dyeing developed according to the discoveries of new dyestuffs, and the application of improved processes, until about the middle of the nineteenth century. Since then, the natural dyestuffs have been gradually giving way to artificial colors derived mostly from coal-tar (see Ccvl-Tar Colors). The liiost important natural and artificial color- ing matters may be found described in articles under their special names. A list of the best- known artificial dyestuffs may be foimd under CO.M.-T.VB CoLOBS." ^lineral and vegetable dyes were formerly considered more lasting than the artificial ones: but this view has. in most cases, positivelv no foundation in fact. The accompany- ing table shows which artificial substances have either partly or completely displaced natural ones in the dyeing of animal and vegetable fibres. Dyestuffs have been roughly divided into two classes, viz., substances which are capable of permanently dyeing fabrics by themselves, with- out the aid of other substances, and substances which cannot dye fabrics without the aid of the so-called 'mordants.' It must, however, be re- membered that the same substance may act as a dye of the first class with animal fibres, and as a dye of the second class with vegetable fibres ; and vice versa. For example, picric acid acts as a 'substantive' color with silk or wool, while cot- ton fabrics cannot permanently be dyed with it. 5I0BDANTS. Tliese are substances capable of combining with other substances (the commer- cial dyestuffs) to form insoluble colored com- pounds. Thus, aluminum salts make an in- soluble red compound with alizarin, and are therefore used as mordants in calico-printing. Ferric salts make, with alizarin, an insoluble dark purple compound, and are likewise cm- ployed as mordants in calico-printing. Soluble mordant salts must themselves be transformed into insoluble compounds before they are allowed to form the dyes, in order to prevent the mor- danting material from being dissolved out of the fabric when the latter is introduced into the dye-bath. Therefore, after the fabric has become impregnated with the soluble mordant salt, it is treated with ammonia, lime, or hot steam — with a view to transforming the soluble salt into an insoluble hydroxide, or an insoluble basic salt; or else the fabric is treated with sodium phos- phate or sodium arsenate — with a view to trans- forming the soluble salt into an insoluble phos- phate or arsenate. In the case of animal fibres, the same end is often attained by simply im- mersing tlie fabric in a boiling dilute solution of the soluble salt, the insoluble mordant being then deposited in the fibre directly. The fabric containing the insoluble mordant is ready to be treated with the dyeing substance, the resulting color of the fabric being evidently that of the compound formed by the latter with the mor- dant. Another method of dyeing with the aid of mordants, extensively employed in calico-print- ing, consists in mixing the dye directly with the soluble form of the mordant and with starch, dextrin, gum, or some other tliickening sub- stance, printing the mixture on the fabric, and then subjecting the latter to a process of steam- ing. The result is of course the same as in case the other methods are employed : for the steaming process has the effect of transforming the soluble into an insoluble form of the mor- dant, the latter then combining with the dye- ing sibstance. ilordants may be either basic or acid, the former combining with 'acid dyes,' the latter with 'basic dyes.' The mordants men- tioned above are basic, and their compounds with dyes are termed 'lakes.' Among the acid mor- dants may be mentioned tannin, or tannic acid. After the" fibre has been impregnated with this mordant in its ordinary, soluble form, it is passed through a weak solution of chloride of tin or of tartar emetic. These produce, respect- ively, the tannate of tin or the tannate of anti- mony (tartar emetic is a compound of anti- mony), and these insoluble tannates further combine into insoluble colored compounds with dyes. "Theobies of Dtetn'G. The question as to whether dveing involves true chemical combina- tion of the fibres with the dyestuffs or not has not yet been definitely answered. Some in- vestigators believe that dyed fibres are merely mechanical mixtures; others hold that dyed fibres are true chemical compounds: finally, still others hold that they constitute what are now termed 'physical mixtures.' or 'solid solutions.' Those who accept the chemical theory argiie that if the dyestuff did not combine chemically with the fibre, then there would be no reason why chemically neutral colored substances should not act as dyes: yet true dyes are genera llv either acid or" basic, while the fibres themselves may be cither basic or acid, or else may include both basic and acid constituents. -Another argu- ment in support of the chemical theory is found in the fact that some substances, while thorn- selves colorless, are capable of imparting color to fabrics when directly applied to them : the view being that colored substances must be transformed cliemically in order to produce color. The principal arguments in favor of the 'l)hysical mixture' theory-, advanced by O. >}■. Witt in 1890. are as follows: (1) Solid fuchsin is green, with a metallic lustre; solutions of