Leather making is a craft of great antiquity but the Industrial Revolution caused a rapid increase of demand for leather. Additional sources of vegetable tannins had to be found and among these was sumac (leaves of various <i>Rhus</i> sp. grown in Mediterranean regions). Leaves of sumac contain a typical gallotannin (MR-1250) as their principal polythenolic component. Most authorities agree that the essence of vegetable tannage is to protect the molecular form of the collagen fibers in the animal skin and that this is achieved by packing the amorphous regions of the fibrillar structure with vegetable tannins. Outlines this process and the possible ways in which the leather, when tanned with sumac, ages and deteriorates. -- AATA -- CAL