Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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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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