MILLING TANBARK FOR TREATMENT OF HIDES
People have used leather since time immemorial. Technology of treating hides has been developing and improving for ages. The craft of processing hides to leather is called tanning.
Tanning industry
To process hides, an abundant source of water is needed. The town of Třebíč being situated in the picturesque valley of Jihlava river was an ideal place for development of the tanning industry. Rawhide was first soaked and rests of fat and flesh were removed from it. Thereafter, fur was removed using lime. The hide changed to pelt, which was soaked in lye to become soft. Only after that the tanner could start the most important stage of the procedure – the tanning itself. Hide was, according to its future kind of use, tanned with alum, fat or tannin. The entire procedure of hide treatment from soaking to tanning was accompanied by distinctive odour.
Processing tanbark to tannin
The windmill of Třebíč crushed tanbark to tannin, which was the necessary raw material for tanners. Most tannin needed for treatment of hides is contained in oak bark. Tannin creates necessary quality of leather, such as stability, elasticity, toughness and water-resistance. Tanbark was gained from 15 – 20-year-old trees. It was peeled from standing trees or removed from felled trees. Tanbark had to be dry, so the long peeled-off pieces of bark were gathered to structures similar to straw men. Dry bark has almost half its original weight.
Milling technology
Dry bark was then processed in a mill with a grinding device. The windmill of Třebíč had five pairs of bark crushers. The bark crushers were small wooden beams with pointed ends. They were powered by a wind wheel via a shaft. They fell down, like hammers, to holes filled up with dry bark.
Treating hides with tannin
Treatment of hides using tannin is a long and exacting procedure. Prepared hides were straightened out in pits. The pits were filled with tannin solution and after that scattered with fine tan. After certain time, the hides were rearranged to let the tannin penetrate to every point. In total, the hides lay in the pits for several months or years.
Used tan served as fuel
The locals would buy the macerated tan from the tanners, as they did not need it anymore, and dry it on streets and between houses. The tan was then used as a cheap source for heating.