Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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sumac

A vegetable tanning material obtained from the dried leaves of certain species of Rhus, especially R. coriaria (from the Mediterranean region—Sicilian sumac) and more recently from various American sumacs, including the dwarf sumac (R. copallina), the white sumac (R. glabra), and the staghorn sumac, (R. typhina). Sumac provides a very desirable tannin where white or light-colored, soft and supple leathers are required. Because it produces such desirable qualities of drape, feel, flexibility, etc., it is used in the tannage of goatskins (morocco leather), skivers, roans, etc. Another important advantage of sumac is that the leather produced with it does not darken upon exposure to light and is less likely to decay than leather produced by use of some other tannins.

In spite of its special value for certain classes of leather, the use of sumac as a tanning agent has declined in recent decades. This decline has been due in part to the development of less expensive tannins, such as wattle, quebracho, and myrabolans for general tanning, and also perhaps to the adulteration of the product by commercial harvesters of sumac in the Mediterranean region.

Good quality sumac is sold in the form of a light, yellowish-green powder, which has a tannin content of about 26 to 27%; however, the tannin content may vary from 25 to 30%. Sumac generally has a higher pH value than other tannin materials in its class, i.e., about 4.0, and also a very high acids and salts content. A large proportion of the salts are weak acids. Sumac, which is one of the pyrogallol class of tannins, is very mild in its action and penetrates the hide substance very slowly. Unlike most of the pyrogallol tannins, sumac does not formBLOOM (1) . Its first recorded use as a tanning agent was in England in 1565. See also: VEGETABLE TANNINS .

(175 , 207 , 363 )




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