SECTION VI.-COMBINATION TANNAGES 



THE formation of leather being due to the adsorption of 

 colloidogenic substances at the interface of the tanning 

 liquor and the hide gel, there is the obvious possibility that 

 several such substances may be used simultaneously, and 

 that the resulting leather may be due to the combined effect 

 of these substances. Indeed, the average vegetable tannage 

 consists of such a combination tannage, each tanning 

 material contributing its own individual tannin and 

 characteristic astringent non-tannins. There is evidently 

 also the possibility that the different types of tannage 

 discussed above might be used either simultaneously or 

 successively, and that a leather might be obtained which 

 combines to some extent the qualities of each of the types 

 in combination. It is such a case that is generally called 

 a " combination tannage." There are many conceivable 

 combinations, and in this section will be chiefly discussed 

 a few which have demonstrated some commercial possi- 

 bilities. Some of these have already received notice in the 

 preceding sections. The manufacture of curried dressing 

 leathers is a combination of vegetable and fat tannages. 

 The manufacture of waterproof chrome uppers illustrates 

 a combination of chrome and fat tannages. The use of 

 " syntans " in conjunction with vegetable tanning materials 

 is also a combination tannage. The case of chamois leather 

 is possibly a combination of aldehyde tannage with fatty 

 acid tannage. Two-bath chrome leather is a combination 

 of chrome, sulphur and fat tannage. Formaldehyde and 

 vegetable tannage is also a known possibility. It is clear 

 that there are possibilities of endless complexity, and that 

 what normally may appear as a simple tannage is in reality 

 a very complex combination tannage. From this standpoint 

 one might instructively consider the successive adsorptions 

 involved in a goatskin tanned first \\ith syntans, then with 



