Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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myrabolans ( myrobalans )

A vegetable tanning material obtained from the dried astringent fruits of certain species of Terminalia, and used extensively in the tanning of leather. The dried fruit is rich in tannin, averaging 30 to 32%, but the percentage varies greatly with different grades and sources.

One of the principal advantages of myrabolan extract, which has to a large extent replaced sumac and plant galls in European tanneries, is its acid-forming properties. It contains 3 to 5% sugars, which is much more than most other tannins contain; consequently fermentation takes place readily in the tan liquor and satisfactory plumping of the hides and skins is obtained in the early stages of tanning. Myrabolan tannin also contains a large proportion of ellagitannic acid, and thus readily deposits bloom. The disadvantages of the tannin are its slow penetration, and its tendency to produce a spongy leather of poor wearing quality. Because of these characteristics, myrabolans is usually blended with other more astringent tannins, e.g., wattle, quebracho, or mangrove, which penetrate faster.

Myrabolans is a pyrogallol class of tannin, with low viscosity, a medium pH (3.2) and salts content, and very high acids content. The tannin also contains chebulinic acid and a fairly high proportion of ellagitannin.

In addition to its used in the tanning industry, myrabolan tannin is also used as a black dye and in the manufacture of some inks. See also:VEGETABLE TANNINS . (175 , 298 , 306 )

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