Russia leather (Russian: юфть or yuft) is a particular form of bark-tanned cow leather. It is distinguished from other types of leather by a processing step that takes place after tanning, where birch oil is worked into the rear face of the leather. This produces a leather that is hard-wearing, flexible and resistant to water. The oil impregnation also deters insect damage. This leather was a major export good from Russia in the 17th and 18th centuries because of its high quality, its usefulness for a range of purposes, and the difficulty of replicating its manufacture elsewhere. It was an important item of trade for the Muscovy Company. In German-speaking countries, this leather was also known by the name Juchten or Juften.
Production Producing the leather involved three processes:
Tanning the leather. This was a bark tanning process, similar to other vegetable-tanned leather. Saturating the tanned hide with birch oil. This is the most distinctive part of the process, giving Russia leather its water resistance and distinctive smell. Dyeing the leather either red or black. This was not an essential part of the process, but was characteristic.
Tanning The tanning process was unexceptional amongst other vegetable tanning processes using tree bark. It followed the usual steps of long soaking and cleaning in water, liming to remove hair, and then the tanning itself. 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. A great quantity of tanbark is required, around 2,880 litres for 150 hides. The tanbark used in Russia was sourced from Salix repens. However, in Siberia the more readily available bast (dark inner bark, beneath the papery bark) of the birch tree was used; it was also reported that spruce bark would be equally effective.
Oiling The oiling process is what really distinguishes Russia leather from others. Birch oil is applied to the flesh side of the leather, soaking through completely and saturating the leather entirely. 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. Seal oil is also reported to have been used. The production of Russia leather is thus a currying or curing process, more than merely tanning.
Birch oil
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. It was a partial pyrolysis and distillation process, similar to the making of turpentine. The papery birch bark was peeled from standing trees and collected. Trees were carefully chosen, older trees being favoured. The season for collecting bark was in late June, when there was the most sap. This bark was then pressed flat under weights and left for a week. Distillation was performed by a process akin to charcoal burning, involving the entire village in a group effort. A large, shallow conical pit was dug, 100 feet (30 m) in diameter and lined with clay. A central drain was constructed, with an underground lined drain leading outwards to a collection pit beyond the burning pit. 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. The pit was then stacked with carefully arranged layers of birch bark, above an insulating and filtering layer of linden husks. The bark was very carefully stacked, so that there was no air space between layers and so combustion could be controlled. A completed pit might be filled ten or twenty feet high (3–6 m). An airtight cover of earth, animal dung and damp fireproof material was placed over the pit, in the manner of a charcoal clamp. A fire of straw was then lit in the centre, spreading slowly outwards into the birch bark. Most of the bark burners would then watch the burn proceeding, carefully sealing air leaks in any areas that were burning too fast. The tar ran down through the bark, filtered through the linden and then through the clay drain and into the collection pit. Others would ladle the collected tar from the pit and into barrels. A burn could go on for ten days continuously, day and night. A quantity of five hundred 'fuhren' of birch bark could give three thousand buckets of tar. A smaller-scale process was also carried out by some individuals using a kettle-like clay pot a couple of feet high. 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. It was likely that other tree species could be found that would produce an oil with similar preservative properties, but the distinctive aroma of genuine Russia leather would require the traditional birch. Cedar oil (a potent bacteriocide) is still used today as a similar preservative ingredient in leather treatments applied to finished leathergoods, such as an ingredient in British Museum leather dressing.
… excerpt ends here. Continue reading the full article.
