The bark of the common European birch (Betula
verrucosa) or (B. pubescens), used in leather
manufacture, particularly in Russia, for hundreds
of years. The outer bark, which peels off easily,
is not used; it is the inner bark from which the
tannin, in the amount of 10 to 15%, and 11%
soluble non-tans, is extracted. Older trees, those
50 to 60 years of age, yield the richest tannin.
Used alone, birch produces a pliable, leather of a
yellowish-brown color; it is, however, more often
mixed with some other tannin, often willow bark.
In addition to tannin, the oil obtained from the
bark is used to dress the leather, imparting to RUSSIA LEATHER its
characteristic odor. Other species of birch have
been used to a limited extent in North America and
India. See also: VEGETABLE TANNINS .