380 The Art of Dyeing. 



are still in a condition to unite with a third body, viz., 

 the colouring matter. 



For this purpose, such solutions or mordants are employed 

 as combine readily with the cotton, when moistened with 

 them, and are not again removed by washing in water. Even 

 by boiling with water, the mordants should remain in com- 

 bination with the fibre. The mordants must not merely 

 cover the fibres, they must penetrate into them and be in- 

 timately united. When this is the case, the colours ap- 

 pear saturated and clear. 



Alumina, iron and tin salts possess these properties in 

 the strongest degree. 



Their application is two-fold, according as light or dark 

 colours are wanted. 



The process of mordanting for light colours, (light, 

 colourless grounds) is performed by moistening the calico 

 with very dilute mordants, and immediately afterwards 

 washing it in water. The mordant is contained in a 

 trough, in which there is a wooden cylinder, which is 

 completely covered by the mordant. The calico is passed 

 under the cylinder, and between two wooden rollers, and 

 pressed ; then rolled upon a third roller, and washed. As 

 it produces a considerable difference whether the calico is 

 a long or short time in contact with the mordant; the 

 greatest uniformity is obtained by allowing the calico to 

 pass twice through the same mordant. In this case, the 

 first untouched end comes last the second time, and is thus 

 equalized. Many solutions of mordants are completely ex- 

 hausted by calico, so as to leave only water behind ; it is, 

 therefore, to be observed, that mordants become weaker in 

 proportion to the number of pieces which come in contact 

 with them. Fresh mordants must, therefore, be added 

 occasionally. The application of mordants for dark colours 

 (heavy colourless grounds) is produced by impregnating the 

 calico with very strong mordants, and then drying it. The 

 impregnation is produced by means of the rollers already 

 described. 



The drying recmires much caution when the grounds are 

 uniformly produced ; it must be done as cmickly as pos- 

 sible, in order that the mordant may not stick to some 

 places more than others. This will be avoided by passing 



