MORDANTS.

5i7

whilst the remaining parts receive less. If, on the other hand, the affinity ofthe mordant for fibre and colour is too feeble in itself, or is over-balanced bysome other body present, the shades resulting will be impoverished, meagre,and probably fugitive.

If a mordant, as is sometimes the case, has a much more decided affinityfor the colouring matter than for the cloth or yarn, the• colour produced isdeposited not on or in the fibre, but at the bottom of the dye-beck, in theshape of a lake or pigment, whilst the goods are merely stained or smearedwith colour. Hence, not every metallic base or salt which has a strongaffinity for colouring matters, and forms abundant and possibly beautiful pre-cipitates in solutions of dye-wares, is fitted for use as a mordant. It isnecessary for the mordant to combine both with fibre and colour withregularity, and not too rapidly, so that the compound formed may not beloosely plastered over the surface of the fibre, but may inter-penetrate itssubstance. The result will, otherwise, be uneven, fugitive, and dull.

Another essential condition is that the mordant must have no injuriouseffedt upon the fibre. If too strongly acid or alkaline it will have a corrosiveadfcion, and the goods, as it is technically called, will be “ tendered.” Thecolouring matter may also be “flattened ” or deprived of its lustre by an ill-compounded mordant. The great majority of mordants are acid, and thepractical difficulty is duly to proportion the acid to the base, so as to producea well-balanced whole. If there is too little acid the mordant becomes too“ dead,” and the base is delivered to the fibre rapidly and irregularly. If theacid is in excess the mordant parts with its base too sparingly and slowly,and the tissue is weakened.

It is also important that mordants should not of themselves affedt the colourof the fibre. When, like the salts of iron, manganese, or copper, they possessan independent tindlorial power, their use is limited to some particular set ofshades. Thus, an iron mordant imparts of itself a buff colour to vegetablefibre. It can, therefore, generally be used only where the shade intended isa black, brown, olive, drab, or some other “sad” colour. Compounds of tinand of alumina, which leave the fibre colourless, can be used for light andbright shades.

Mordants, as a matter of course, are presented to the fibre and to the colourin a liquid state, but they must be capable of becoming insoluble as the com-bination is accomplished. This change of condition, from a soluble to aninsoluble state, is brought about in several ways. Frequently it is a case

glossy. This is a serious difficulty for the jobbing dyer, since garments which have been wornalways present inequalities of surface, and are, therefore, when re-dyed certain to appearspotty. We may here briefly refer to the different “ appetite ” for mordants and colours pre-sented by different growths of wool. Two different wools treated in exactly the same mannerwith the same quantities of the same dye-wares do not necessarily take the same intensity,sometimes not even the same tone, of colour. The climate where the wool is produced, thebreed of the sheep, the nature of their food, and possibly other causes have a modifyinginfluence. Hence woollen manufacturers who pride themselves on the uniformity of theirresults are generally careful to use, year by year, the same growths of wool for the same classof goods.

The varying affinities of different kinds of cotton for colour have been pointed out in anearlier portion of the work: p. 28.