The following summary of the
tanning process is adapted from
here.
After removing the horns and hooves, and trimming unusable portions of the hide (belly, areas around head and legs, udders, and hide edges), the tanner washed blood, dung, and dirt from the hide.
Next, fat, hair, and flesh were removed—usually by immersion in a solution of lime or urine. (In sufficiently warm conditions, the hide could be sprinkled with urine and folded hair-side inward to encourage rotting of the hair follicles.)
After treatment, loosened hair was scraped from the hide with a blunt single-edged knife, and flesh was removed with a sharper, double-edged knife.
After rewashing, the hide was de-limed and and softened by one of two alternate processes:
a) an alkali-rich process of immersion in warm dog dung or bird droppings
b) drenching in a solution of barley or rye in stale beer or urine
The hides were washed again, then agitated in a solution of crushed oak bark. After being layered with ground bark, the hides were transferred to a pit filled with a weak tanning solution. Later, they would be moved to a tank containing a high concentration of tannins, in a process that required at least a year to complete.
After 12-18 months soaking in tannin solutions, the tanned hides were rinsed, and smoothed using a two-handled setting pin. Next, they were dried slowly in a dark shed before being sent to a currier, for stretching, shaving, and softening by the application of greases, sometimes brain.
en.wikipedia.org
