Tanning Materials

plant parts or extracts containing tannins, which are used in leatherworking to tan hides.

Among the main tanning materials are the wood of the oak and chestnut (together with the bark); the bark of the willow, larch, and fir; and certain roots (knotweed, rhubarb, and thrift). In the oak, the tannins occur in all parts of the plant, but only the stumps and the wood and bark of the trunk and large branches, which are not suitable for use as lumber, are used as tanning materials. The quantity of tannins in oak varies from 4 to 6 percent, depending on the species and the region and time of procurement; for chestnut it varies from 7 to 8 percent; and in willow, larch, and fir tannides are found in the bark (8-20 percent). The possibilities for annual procurement of fir and larch bark are virtually unlimited. The content of tannins in root tanning materials is as much as 22 percent in knotweed, 14.5 percent in rhubarb, and 11-21 percent in thrift.

In addition to the plant tanning materials mentioned above, factories sometimes process valonia, quebracho, acacia, mangrove, myrobalan, and gallnuts. Valonia (the cups of acorns from oaks growing mainly in Asia Minor and southern Europe) contains an average of 23.5 percent tannins, and the scales that cover the acorn cup contain as much as 45.5 percent; therefore, they are separated out and marketed in the form of a separate tanning material known as trillo. Quebracho wood contains about 19 percent tannins; acacia bark, an average of 31.5 percent; mangrove bark, 14-48 percent; myrobalan fruit, 35-50 percent; and gallnuts, 19-77 percent, depending on the species.

Tanning materials have not been used in leather production for the layer tanning method in the USSR since the early 1930’s. With the development of the Soviet tanning-extract industry, all tanning materials are processed to make extracts.