192 ANIMAL PROTEINS 



oak bark, " retanned " in sumac, mordanted with chrome, 

 dyed with coal-tar dyestufls and finally oiled with linseed 

 oil. It will be easily seen that in a very strict sense nearly 

 all tannages are combinations. 



Usually, however, the term " combination tannage " is 

 confined to those cases where the main tanning agents not 

 only differ in type, but where none are in predominant 

 quantity. A typical case is that of " semichrome leather," 

 in which a vegetable tannage is succeeded by a chrome 

 tannage. E.I. tanned sheep and goat skins are rather 

 heavily " stripped " of their vegetable tannage and heavy 

 oiling, by drumming with warm soda solutions, and after 

 washing with water are chromed with the one-bath process ; 

 they are neutralized, dyed, fat liquored and finished for glace 

 upper leather. 



In a precisely similar way kips and split hides which have 

 received vegetable tannage are stripped and retanned in 

 chrome and finished as for box calf, of which they are a good 

 imitation. Such vegetable-chrome combination tannages 

 possess many of the properties of chrome leather. 



To chrome the pelt first and afterwards to subject it to 

 vegetable tannage is also an obvious possibility, but has not 

 yet been made a commercial success in this country, but has 

 been increasingly used in the U.S.A. during the War. 



Another typical case of combination tannage is the 

 dongola leather produced by the use of gambier and of 

 alum and salt. This is a vegetable-alum combination, and 

 yields a good quality leather for light uppers, gloves, etc. 

 Goatskins for " glazed dongola " are paddled tanned in 

 gambier liquors, and alum and salt are subsequently added. 

 They are tanned in 24 hours, well washed, and are fat 

 liquored without ageing. The E.I. tanned skins may also 

 be stripped with soda, and retanned in alum and salt, using 

 flour also if desired. Dull dongola are first tawed and then 

 retanned in gambier liquor. " Suede " and " velvet calf " 

 are also tawed and retanned with gambier. 



Yet another case of combination tannage is that of sheep- 

 skins for glace uppers, which are first tawed thoroughly 



