19*4 DYEING. 



aljly to the fullness of the black. The decoction 

 of logwood which is reddish becomes black by 

 sulphate of iron. 



To dye cloth or wool black, the first process 

 generally is to dye it blue, which renders the black 

 to be given more intense. If the cloth be coarse, 

 and the blue dye too expensive, a brown dye may 

 be given by means of walnut peels. It is then 

 boiled for two hours in a decoction of nut galls, 

 and then for two hours more in a bath composed 

 of logwood and sulphate of iron, at a scalding heat, 

 but not boiled. During the operation, it must be 

 frequently exposed to the air. The common pro- 

 portion are five parts of galls, five of sulphate of 

 iron, and thirty of logwood, for every 100 of cloth. 

 For coarse cloths the previous blue dye is omitted. 

 The cloth is then washed and fulled. 



Silk is dyed black as follows. After boiling it 

 with soap, it is galled, and afterwards washed. It 

 combines with a considerable portion of the astrin- 

 gent principle, and increases in weight. It is then 

 dipped into a bath of sulphate of iron and gum 

 arable. 



Cotton and I'men are first dyed blue, then steeped 

 in a decoction of galls, and alder bark. It is then 

 put into a batli of acetite of iron, taken out and 

 exposed to the air. This operation is repeated 

 several times. 



Of dyeing Compotincl Colours. 



Compound colours are produced either by mix- 

 ing together two or more simple ones, or by dyeing 

 cloth first one simple colour and afterwards 

 another. 



