Bark mill

Bark mills were used to grinding or cutting the roots, branches, or barks of different species of trees, to form a fine powder (tanbark) suitable for the operations of the tanner in the preparation of leather for clothes, boots, furniture, etc. The powdered wood more quickly yields up the tannin required for the tanning process. The dried bark was often stored in bark houses.

Water-, steam-, horse- or ox- and wind-powered bark mills existed. Water-powered bark mills were sitting alongside rivers and leats were dug to bring water to the wheel.

A barker was a person who stripped bark from trees to supply bark mills.

Various forms of machinery were used in the process of chopping, grinding, riddling and pounding the bark, such as Farcot’s bark-cutting machine, extensively used in France, Weldon’s bark-grinding mill, and another grinding mill, much used in America and known as Wiltze’s or Catskill’s mill.

Bark tanning or vegetable tanning is part of the ancient process of creating durable, water repellent leather with a lot of 'body'. It can be done to most types of skin, but it is usually reserved for tanning leathers from large and thick hides such as cattle, horses, and pigs. The leather produced has been commonly used for saddles, canteens, stiff shoes, belts, wallets, holsters, harnesses, helmets, pouches, trunks, shields and gun cases. It was also used as an integral part of bellows, hinges, wagon wheels, etc. Vegetable tanned hide is flexible and is used for luggage and furniture.

Mineral tanning, being cheaper and faster, replaced the use of bark and mainly uses chromium Sulphate. Once the desired level of penetration of chrome into the substance is achieved, the pH of the material is raised again to facilitate the process. In the raw state chrome tanned skins are blue. Chrome tanning produces a stretchable leather which is excellent for use in handbags and garments.

Tawing uses alum and aluminium salts, together with egg yolk, flour, and other salts. The leather becomes 'tawed' by soaking in a warm potash alum and salts solution. The process increases the pliability, stretchability, softness, and quality of the leather. The addition of egg yolk and flour to the standard soaking solution further enhances its fine handling characteristics. Then, the leather is air dried for several weeks, which allows it to stabilize. Tawing is used on pigskins and goatskins to create the whitest colour.

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Wikipedia