1835.] Calico- Printing. 9 



are usually called chemical colours.* The mixture is allowed 

 to dry on the cloth, which is then merely washed with 

 water. When colours are applied in this way they are 

 easily altered by soap, exposure to the light, &c. Hence, 

 in common language, a chemical colour means a fugitive 

 colour. The colours produced in this way, are pink from 

 Brazil wood, peach wood, and cochineal ; purple from log- 

 wood, and yellow from Persian berries. 



Perchloride of tin is much used in another common pro- 

 cess of calico-printing, known technically, by the apella- 

 tion of steam colours. It is decomposed and converted 

 into stannate of potash. The whole piece of cloth is im- 

 mersed in the liquid containing the stannate of potash, and 

 dried. The peroxide of tin is then deposited on the cloth, 

 by immersing the piece in a solution of sal ammoniac, or sul- 

 phate of magnesia ; but most commonly, in a very weak 

 solution of sulphuric acid. The different colouring matters, 

 previously thickened with starch, are then printed on the 

 cloth, and the whole subjected to the action of steam. By 

 the joint action of moisture and heat, a combination takes 

 place between the colouring matter and the oxide, which is 

 thus rendered insoluble. And no considerable quantity of 

 water is ever present to carry off the colouring matter, be- 

 fore it has .combined with the mordant. 



3. Peroxide of iron. — This metallic oxide is much used as 

 a mordant. It is employed in the state of acetated pro- 

 toxide of iron, formed by dissolving iron in pyrolignic acid. 

 Within a few days after it has been applied to the cloth, 

 especially if exposed to a moist atmosphere, it loses its acid, 

 and the iron becomes peroxidized. 



Acetate of iron, of the specific gravity 1*05 gives a black, 

 with madder. Various shades of purple are obtained by add- 

 ing different portions of the mordant and dye-stuffs. Diffe- 

 rent shades of red, from brown, red, to pink, are obtained in 

 the same way, substituting the alum mordant of various 

 strengths for the iron. Chocolates are got by mixing the 



* A very general error prevails with regard to Chemical colours, that it is the 

 mode of applying them which renders them fugitive. It is, because Chemical 

 colours are made with changeable materials, that they are more easily acted on 

 than madder colours. Brazil pink for instance, is equally acted upon by light 

 and soap when dyed. 



