tanning, process by which skins and hides are converted into leather. Vegetable tanning, a method requiring more than a month even with modern machinery and tanning liquors, employs tannin; its use is shown in Egyptian tomb paintings dating from 3000 B.C. Mineral tanning includes tawing, or alum tanning, another ancient method, and chrome tanning, the process most common today, based on the use of chrome salts and requiring only a few hours. Known as early as 1856, chrome tanning was first patented in the United States by Augustus Schultz in 1884. In oil tanning, or chamoising, the pelts are treated with fats and hung to dry; the leather is commonly napped on both sides and is very absorbent. The most recently developed tanning process employs artificial agents (syntans). Most heavy leathers, such as sole leather, are vegetable tanned; many light leathers are chrome tanned. The Native Americans of North America used the chamois method, employing the fat, livers, and brains of animals. Their tanned white buckskin was highly esteemed, especially for clothing, both by Native Americans and by colonial pioneers. In the tanyards of European settlers tanners used oak and hemlock bark; gallnuts; the wood, nuts, and leaves of the chestnut tree; and the leaves of sumac.