human
or
gpt
in which the mechanical operations are different in aim and method. In the first pits entered by the goods there is rapid adsorption in spite of the low concentration and small astringency, and the great aim is to obtain evenness of action and a good level colour. It is also necessary to maintain the rate of adsorption. All the aims are attained by frequently moving the goods. Heavy leather is suspended vertically in the pits of tan liquor and handled up and down as well as forward from pit to pit. Such pits are termed
human
In the earliest suspenders it is indeed advantageous to have the goods in constant motion. This is done by suspending on wooden frames which are rocked gently by mechanical power; such pits are termed
gpt
For dressing leather in which firmness and smooth grain are not so essential, the goods may be paddled in the first liquors. This is occasionally done with stronger liquors for the express purpose of working up the
human
pattern. The goods after passing through the suspenders are usually passed to