172 ANIMAL PROTEINS 



obtain a stuffing material with less crystalline texture. 

 The use of 10-30 per cent, rosin in the stuffing grease 

 is also usual. This prevents the leather from being so 

 slippery when in wear. The stuffing should take place 

 at temperatures from I5o-i95 F., according to the 

 melting-point of the grease employed. The bends are 

 taken out and laid in pile to cool and set in a flat condition, 

 and are then finished. 



The chrome tannage of butts for strapping and harness 

 backs, and for motor butts and picking bands may be 

 similar to that for chrome sole, but drum tannages are 

 more common and the two-bath process is often used. In 

 the latter case the acid chroming bath is preferred, using 

 6 per cent, of dichromate and of acid, with up to 15 per 

 cent, of salt, and reducing with 15 per cent, thiosulphate 

 and acid as needed. This process assists in the production 

 of the light colour which is preferred in the case of some 

 of these leathers. 



Strap butts after tanning are very thoroughly washed 

 with cold water in pits, and repeatedly struck out by 

 machine between the washings. They are then oiled with 

 heavy mineral oil, and stretched by powerful machines. 

 They are dried and curried during the stretching. Degras, 

 wool fat and vaseline are greases used, and the drying 

 and stretching finished off at 120 F. They are then 

 fluffed on the flesh, French-chalked and heavily rolled. 



Harness backs are neutralized, machine sammed, and 

 lightly fat liquored with 4^ per cent. soap. They are then 

 struck and oiled with heavy mineral oil and dried for 

 stuffing. Hand stuffing, drum stuffing, and " burning in " 

 are all used (see Part I., Section IV.). Stearin, paraffin 

 wax, ceresin wax, wool fat, sod oil and mineral oil are the 

 greases employed. The butts are blacked after stuffing 

 with lamp black and oil, glassed well and buck-tallowed 

 on the grain. 



Motor butts are fat liquored lightly, using soap only. 

 They have to be softened, therefore, during the drying 

 by being mechanically worked. A boarding machine is 



