152 DYES. 



BLACK DYES. 



These are of the same ingredients as writing-ink ; the black 

 dye, therefore, usually contains oxide of iron, tannin, and 

 gallic acid ; logwood and the acetate of copper imparting, 

 when added, a blue shade. As the immediate application of 

 the black dye would, through quantity, be apt to injure the 

 cloth, the best black woollen cloths are first dyed red witli 

 madder, and blue with indigo. Frequently ordinary wool- 

 lens receive for the first dye logwood only, with a salt of cop- 

 per ; but a black is obtained which always turns brown and 

 rusty-colored in wear. 



Black silks have generally a decoction of galls applied 

 first ; the galls, being more attracted by the silks than the 

 iron, are therefore the true mordant. After this the silk is 

 subjected to alternate baths of sulphate of iron and a decoc- 

 tion of logwood, repeated till a deep black appears. Cotton 

 has usually the iron applied first. 



Black vats, with iron and various vegetable matters, are 

 frequently kept for an immense length of time unemptied, as 

 it is believed they improve by age. 



The Red maple (Acer rubrum) of the United States, ap- 

 plied with the sulphate or acetate of iron, gives, as discovered 

 by Dr. Bancroft, a more perfect black than any of the com- 

 mon vegetable dyes. With alum it yields a permanent cin- 

 namon-color, both upon cotton and wool. The bark and 

 leaves are both used. 



The common Nutgall, as is well known, is an excres- 

 cence produced by the puncture of an insect, a species of 

 cynips, upon an Asiatic species of oak ( Quercus infectoria). 

 Besides tannin and gallic acid, Dr. Bancroft has detected a 

 coloring matter. With an aluminous basis, galls yield a 

 fawn or light cinnamon color. 



The bark of Butternut (Juglans cathartica) gives to cot- 



