DYEING 171 



colour within its fibre, its lightness assisting this action, as the precipitate -will 

 remain suspended in water for days before it will subside. Vegetable fibre takes up 

 this dye as easily as animal, but whether by an attraction for the stuff, or by a 

 mechanical capillary attraction of the fibre is not so easily determined. A piece 

 of stuff suspended in a vessel filled with water, having in it some insoluble cartha- 

 mine, all the colouring particles will flow to and combine with the fibre from 

 a considerable distance, giving a proof of the existence of some force drawing them 

 together. 



Such then are the various conditions and principles involved in the processes of 

 fixing the dye within or upon the stuff. 



During the operations of dyeing there are certain circumstances which have to be 

 attended to, in order to facilitate and affect certain hues or tints of colour. Thus, 

 witli many of the colouring substances, heat not only favours but is necessary for 

 the solution of the dye, and also its combination with the stuff or mordant. Decoctions 

 of woods are always made by hot water, and the dyeing processes with decoctions are 

 in hot liquor. When the colouring matter of quercitron bark is extracted by boiling 

 water, the colour produced upon the stuff will be a rich amber yellow, but if the 

 extract be made by water at 180 Fahr., a beautiful lemon yellow will be the dye pro- 

 duced by it, using the same mordant in each case. Colours dyed by madder and 

 barwood must be done at a boiling heat during the whole process, or no dye is effected. 

 Sumach, another astringent substance, is most advantageously applied at a boiling 

 heat ; and in order to have a large body of this dye fixed upon the stuff, it should be 

 immersed in the liquor while hot and allowed to cool together, during which the 

 tannin of the dye undergoes some remarkable change in contact with the stuff. 

 Safflower dyes are kept cold, so are tin bases, Prussian blues, and chrome yellows : by 

 applying heat to the last a similar result is effected to that with bark ; instead of a 

 lemon yellow, an amber yellow will be obtained. Almost all colours are affected less 

 or more by the temperature at which they are produced. Some mordants are fixed 

 upon the stuff by heat, such as acetate of alumina ; the stuff being dried from a solu- 

 tion of this salt at a high temperature loses part of the acid by being volatilised, and 

 there remains upon the fibre an insoluble suboxide, which fixes the dye. These 

 remarks respecting the methods apply more particularly to vegetable stuffs, as cotton, 

 and in many cases also to silk, but wool is always dyed at a high heat. Although 

 wool seems to have a much greater absorbing power than cotton, the latter will absorb 

 and become strongly dyed in a cold dye-bath, in which wool would not be affected ; 

 but apply heat and the wool will be deeply dyed, and the dye much more permanent 

 than the cotton. 



The permanence of colours is another property to be carefully studied by the 

 practical dyer, as the colour must not be brought under circumstances that will destroy 

 its permanency during any of the operations of the dye-house. The word ' permanent,' 

 however, does not mean fast, which is a technical term applied to a colour that will 

 resist all ordinary operations of destruction. For instance, a Prussian blue is a 

 permanent colour, but not a fast colour, as any alkaline matter will destroy it ; or a 

 common black is permanent, although any acid matters will destroy it ; while Turkey 

 red is a fast colour and not affected by either acid or alkaline matters. A few of the 

 circumstances affecting colours in the processes they are subjected to may be referred 

 to in this place. If, for instance, the air in drying the dyed stuff in a hot chamber be 

 moist, there is a great tendency to the colour being impaired in these circumstances. 

 For example, a red colour dyed with safflower will pass into brown, a Prussian blue 

 will pass into a grey lavender, whilst chrome yellows take an amber tint. Almost all 

 colours are more or less affected by being subjected to strong heat and moisture ; even 

 some of those colours termed fast are affected under such circumstances. A dry heat 

 has little or no effect upon any colour, and a few colours are made brighter in their 

 tint by such a heat, as chrome orange, indigo-blue, on cotton, &c. 



Some of these effects of heat and moisture differ with different stuffs ; thus indigo- 

 blue upon cotton is not so much affected as indigo-blue upon silk, while safflower-red 

 upon cotton will be completely destroyed before the same colour upon silk will be 

 perceptibly affected. The same colouring matter fixed by different mordants upon 

 the same stuff is also differently affected under these conditions. 



Light is another agent effecting a great influence upon the permanence of colours, 

 which should be also considered by the dyer. Reds dyed by a Brazil wood and a 

 tin mordant, exposed to the light, become brown ; Prussian blue takes a purple tint ; 

 yellow becomes brownish ; safflower-red yellowish, and these changes are facilitated 

 by the presence of moisture ; such as exposing them to strong light while drying from 

 the dye-bath, either out or within doors. The direct rays of the sun destroy all dyed 

 colours ; even Turkey red yields before that agency. 



Boiling was formerly prescribed in France as a test of fast dyes. It consisted in 



