1835.] Calico- Printing . 7 



have imbibed the mordant, while the other parts of the 

 cloth remain white. Sometimes acids, or other substances, 

 are printed on cloth already dyed, to remove the colour 

 from certain portions of jt which are to be left white, or to 

 receive some other colour. 



Occasionally, substances are printed on cloth before it is 

 dipt into the indigo vat, to prevent the blue colour from 

 becoming fixed on those parts to which they are applied. 

 Substances possessed of these properties are called resist 

 pastes. 



It is a very common practice to communicate mordants 

 and colouring matters to cloth at the same time. 



We must give a sketch of the different substances thus 

 applied, before proceeding to detail the different processes. 



I. MORDANTS. 



The term mordant, is applied by dyers to certain sub- 

 stances with which the cloth is impregnated before it is 

 dyed, otherwise the colour would not fix, but would dis- 

 appear on washing or exposure to the light. The name 

 was given by the French dyers, (from the Latin word mor- 

 dere, to bite,) from a notion entertained by them that the 

 action of mordants was mechanical, that they were of a 

 corrosive, or biting nature, and served merely to open the 

 pores of the cloth, into which the colouring matter might 

 insinuate itself. It is now understood that their action is 

 chemical. They have an affinity to the cloth, which causes 

 them to adhere to it ; while the colouring matter has an 

 affinity for, and adheres to the mordant. 



The usual mordants employed by the calico-printer, are 

 the three following : — 



1. Alumina, or the alum mordant. This mordant is made 

 by dissolving alum in water, and adding acetate of lime to 

 the solution. The liquid has a specific gravity of 1*08, 

 and contains about as much alum undecomposed, as the 

 liquid can hold in solution. For particular purposes, 

 calico-printers make a mordant by mixing three parts of 

 acetate of lead with four of alum. This mordant consists 

 of a mixture of acetate of alumina and alum ; for, about a 

 third part of the alum remains undecomposed. 



When cloth is impregnated with this mordant, such is 



