The bark of the Cassia auriculata, and the milky juice of the Asclepias gigantea, are used for tanning in India.
The red astringent gum obtained from Butea frondosa, a middling size tree, common in Bengal and the mountainous parts of India, is used by the natives for tanning. English tanners, however, object to its use on account of the color which it communicates to the leather.
The barks of the Mora excelsa, Benth; Courida (Avicenna nutida), cashew (Anicardium occidentale), guava and hog-plum (Spondius lutea, Linn.), have all been successfully used for tanning in Demerara and the West India Islands, where they are very abundant. Specimens were sent from British Guiana.
The root of the Palmetto palm (Chaemaerops Palmetto) is stated to be valuable for the purposes of tanning. The leaves of Nerium Oleander contain tannic acid. The bark of a species of Malphigia is much used by the Brazilians.
The panke (Gunnera scabra) is a fine plant, growing in Chili, on the sandstone cliffs, which somewhat resembles the rhubarb on a gigantic scale. The inhabitants eat the stalks, which are subacid, tan leather with the roots, and also prepare a black dye from them. The leaf is nearly circular, but deeply indented on its margin. Mr. Darwin measured one which was nearly eight feet in diameter, and therefore no less than twenty-four in circumference. The stalk is rather more than a yard high, and each plant sends out four or five of these enormous leaves, presenting together a very noble appearance.
The barks replete with the tanning principle should be stripped with hatchets and bills from the trunk and branches of trees in spring, when their sap flows most freely. The average quantity of oak bark obtained from our forests is estimated at 150,000 tons annually, of which Ireland and Scotland furnish but a very small quantity.
The following table, given by Dr. Ure, shows the quantity of extractive matter and tannin yielded by different substances:—
| In 480 parts | In 100 parts | |
| by Davy. | by Cadet. | |
| Sicilian sumach | 78 | — |
| Malaga ditto | 79 | — |
| Souchong tea | 48 | — |
| Green tea | 41 | — |
| Bombay catechu | 261 | — |
| Bengal ditto | 231 | — |
| Nutgalls | 127 | 46 |
| Bark of pomegranate | — | 32 |
| Bark of Virginian sumach | — | 10 |
| Bark of Carolina sumach | — | 5 |
Catechu and Gambier are very valuable for tanning, and are alluded to under the heads GAMBIER and ARECA PALM.
CATECHU is obtained from the Acacia Catechu, an arboreous tree growing from fifteen to twenty feet high, with a brown and scabrous bark. The interior wood is brown, dark red or blackish, and the exterior white, one or two inches thick. It inhabits various parts of the East Indies, of which it is a native, and is also now common in Jamaica. It bears whitish or pale yellow flowers.