hemlock (bark)
A vegetable tanning material derived from either
the Eastern (Canadian) hemlock, Tsuga canadensis,
or the Western hemlock. T. heterophylla, the
former being the best known and most used. The
bark of the eastern hemlock has an average tannin
content of 15 to 16%, while that of the western
variety average 10 to 11%. One characteristic of
the bark is the lack of any appreciable quantity
of sugars, with the result that it does not
produce acids by fermentation. Because of this, it
is customary to add a small amount of organic acid
to hemlock tan liquor. Another characteristic is
the reddish color it imparts to the leather, which
can be modified considerably by the addition of
other tanning materials, such as oak bark or
quebracho.
Hemlock bark was for many years the most important
tanning material used in the United States and
Canada, and was, along with oak bark, the
principal material used in tanning leather on a
commercial scale.
It was responsible for the characteristic "red"
leather produced in America in the 19th century.
See also: VEGETABLE
TANNINS . (175 )
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