No. 129. 439 



We must except indigo ; after which the dyer is not possesssed 

 of a dye that I know of, that will color so permanently, that 

 water will not discharge it. 



This apparently insurmountable difficulty has been overcome 

 by an ingenious contrivance. Simply by immersing the cloth to 

 be dyed in certain prepared substances, which makes the dye 

 permanent, that, without the use of this preparation, would be- 

 come fugitive. This bond of union between the dye-stuff and the 

 cloth has received the appellation of mordants. 



The term mordant (from the Latin word mordere, to bite,) is 

 applied to certain substances, with which the cloth to be dyed 

 must be impregnated. The red color given to cotton by madder 

 would not hold, unless the cloth had been previously steeped in 

 dilute salt of alumina. The cloth decomposes the salt of alumina, 

 and combines with a portion of alumina. The red coloring prin- 

 ciple of the madder, possessing an affinity for the alumina, com- 

 bines immediately with it, consequently, the alumina is held by 

 the cloth, and the coloring matter by the alumina, thus the dye 

 becomes fixed. The same color may form various dyes, by 

 ©hanging the mordants. If, for example, you color with cochi- 

 neal, and use the aluminous mordant, the cloth will become 

 crimson; if oxide of iron is used with it, black is produced. 

 These mordants are composed of earths, tannic acid, and metallic 

 oxides. 



That most generally made use ot is alumina, either in the form 

 of common alum, or acetate of alumina. Alum is composed of 

 potash, alumina, and sulphuric acid. Nearly all the metallic ox- 

 ides appear to have an affinity to cloth. However, the oxides of 

 iron and tin are the most used as mordants. 



AVhen the oxide of tin is employed, it is in the state of proto- 

 chloride and acetate of tin. By this means alone can scai-let, 

 the brightest of all known colors, be produced. Tannic acid 

 from nutgalls and sumach has a strong affinity for cloth. Oil is 

 frequently used for dyeing linen cloth, &c. Cloth intended to be 

 dyed, should first be made perfectly white, as colored materials 

 will invariably interfere more or less with the dye. 



