168 ANIMAL PROTEINS 



The chroming bath contains 5 per cent, dichromate, 5 

 per cent, hydrochloric acid, and 10 per cent. salt. After 

 the skins are thoroughly penetrated they are horsed over- 

 night and reduced with 20 per cent, thiosulphate, up to 

 7 per cent, of hydrochloric acid being added after half 

 an hour in thiosulphate only. 



Alum pickled or tawed skins are wet back by drum- 

 ming for about an hour in water, and are then tanned by 

 the one-bath process in drums. Only a few hours are 

 needed. Towards the end of the operation about \ per 

 cent, of bicarbonate of soda may be added to the chrome 

 liquor. Acid pickled skins may be wet back with 10 per 

 cent, salt, and depickled by adding a basic alum solution 

 and the chrome tannage superimposed after about half 

 an hour without handling the goods. The basic chrome 

 alum liquor is suitable for this purpose. 



In finishing glace sheep much the same methods are 

 used as in the case of glace goat. Sheepskins are perhaps 

 more lightly fat liquored, being naturally soft and porous. 

 Degreasing is often necessary to obtain an even finish. 

 As sheep gives an empty pelt and chrome an empty tannage, 

 a slight retannage is often given in gambier, especially for 

 blacks, in which case the skins are well mordanted. This 

 retannage makes the leather less stretchy. I^ogwood and 

 iron blacks are usual. For colours, fustic or sumach are 

 the usual mordants, with tartar emetic to fix. If for glove 

 leathers, skins pickled in alum and salt or tawed should 

 be preferred, and flour may be used in the fat liquor. 



Sheepskin splits are sometimes given a chrome tannage 

 and finished as chrome chamois. This leather may be 

 used for linings, but not for polishing silver on account 

 of the sulphur originating from the reduction bath. The 

 splits are puered heavily, and pickled in 6 per cent, vitriol 

 a and 24 per cent. salt. They are paddled in this pickle 

 liquor, and 4 per cent, dichromate added in successive 

 portions. The fleshes are horsed overnight and reduced 

 in 15 per -cent, thiosulphate, to which a little hydrochloric 

 acid is added if needed. 



