It was considered, even into the nineteenth century, that although the manufacture of 'Russia leather' could be successfully undertaken in the rest of Europe, production of the necessary birch oil would still require import from Russia or Poland. Ī smaller-scale process was also carried out by some individuals using a kettle-like clay pot a couple of feet high. A quantity of five hundred 'fuhren' of birch bark could give three thousand buckets of tar. A burn could go on for ten days continuously, day and night. Others would ladle the collected tar from the pit and into barrels. The tar ran down through the bark, filtered through the linden and then through the clay drain and into the collection pit. Most of the bark burners would then watch the burn proceeding, carefully sealing air leaks in any areas that were burning too fast. A fire of straw was then lit in the centre, spreading slowly outwards into the birch bark. An airtight cover of earth, animal dung and damp fireproof material was placed over the pit, in the manner of a charcoal clamp. A completed pit might be filled ten or twenty feet high (3–6 m). The bark was very carefully stacked, so that there was no airspace between layers and so combustion could be controlled.
The pit was then stacked with carefully arranged layers of birch bark, above an insulating and filtering layer of linden husks. This drain was protected by a strainer dome to avoid ash entering the tar drain and to separate the burning bark from the flammable tar. A central drain was constructed, with an underground lined drain leading outwards to a collection pit beyond the burning pit. A large, shallow conical pit was dug, 100 feet (30 m) in diameter and lined with clay. This bark was then pressed flat under weights and left for a week.ĭistillation was performed by a process akin to charcoal burning, involving the entire village in a group effort. The season for collecting bark was in late June, when there was the most sap. Trees were carefully chosen, older trees being favoured. The papery birch bark was peeled from standing trees and collected. It was a partial pyrolysis and distillation process, similar to the making of turpentine. Production of 'degot', the birch oil or birch tar for leathermaking was a specialist craft and practised by only a few villages that then supplied other leathermaking sites. The production of Russia leather is thus a currying or curing process, more than merely tanning. Seal oil is also reported to have been used. Care is taken that it is only applied to one side of the leather, keeping it away from the grain side to avoid discolouration and poor dyeing later. Birch oil is applied to the flesh side of the leather, soaking through completely and saturating the leather entirely. The oiling process is what really distinguishes Russia leather from others. The tanbark used in Russia was the poplar willow Salix arenaria or in Siberia the more readily available bast (dark inner bark, beneath the papery bark) of the birch tree it was also reported that spruce bark would be equally effective. A great quantity of tanbark is required, around 2,880 litres for 150 hides.
Tanning steeps the leather in a solution of tanbark for around five weeks, with twice daily agitation and weekly replacement of the 'tan', or tanning solution. It followed the usual steps of long soaking and cleaning in water, liming to remove hair, and then the tanning itself. The tanning process was unexceptional amongst other vegetable tanning process using tree bark. This was not an essential part of the process, but was characteristic.
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