162 APPLIED SCIENCE 



189. Dyeing and Dyestuffs. The process by which color- 

 ing is added to fabrics by means of dyestuffs is called dyeing. 

 Dyeing may be done in one of three ways: (1) by immersing 

 loose raw material, such as unspun cotton threads, in the 

 coloring solution; (2) by immersing yarn before it is woven; 

 and (3) by immersing the woven cloth itself. The latter 

 method is the cheapest and the one most commonly used. 



Dyestuffs are obtained from animals, vegetable substances, 

 minerals, and organic materials. Examples of the dyes 

 obtained from these four classes of materials are furnished 

 by cochineal coloring matter, indigo, Prussian blue, and 

 aniline dyes respectively. 



Fibers of animal origin, such as silk or wool, can be dyed 

 by simply immersing them in the color solution, but materials 

 such as linen and cotton, which have a vegetable origin, 

 will not hold some dyestuffs. Therefore, in the case of these 

 latter fabrics it is often necessary to apply to the cloth or 

 to the coloring solution some chemical salt, such as alum, 

 in order to make the dyestuff adhere to the material. The 

 chemical salt applied for this purpose is called a mordant. 



190. Printing on Fabrics. It is often desirable to print 

 a colored design on a fabric that has been already dyed. 

 There are three modern methods of printing patterns: 

 direct printing, discharge printing, and resist printing. 



In direct printing the fabric is passed between polished 

 copper rollers, on the surface of which a design has been 

 engraved. When there is to be more than one color in the 

 design a separate roller is necessary for every additional 

 color. The coloring material, which consists of dyestuffs 

 made into a paste, is placed beneath the rollers, a single 

 color for each roller. As each roller rotates it comes into 



