Vegetable tanning with tannic acids is the oldest method. Used primarily for heavy cattle hides, the process may take a month or more. The tanned leather is then bleached and impregnated with natural oils and greases. The final product of the vegetable tanning process is a firm, water-resistant leather used chiefly in shoe soles but also in upholstery, luggage, saddlery, and industrial belting. Hides and skins are tumbled in huge drums partially filled with chrome-salt solutions that produce a light blue green leather, which is then cleaned, dried, and smoothed by machine.
Chamois leather is napped, or sueded, on both sides and is very absorbent.
Finishing After the leather is tanned, machines split it into flesh and grain layers. The leather must now be dried. To prevent shrinkage it is often stretched on frames or smoothed flat on a glass or metal plate before being placed on a conveyor and passed through the drying cabinet. Dried leather is generally too stiff, and it may be conditioned by spraying with water until sufficient moisture has been absorbed to ensure flexibility. Various types of finishes are then applied.