ABSTRACT
Leather, in contrast to parchment, is the product of the tanning process on animal skins which occurs with the treatment of hides with vegetable tannin extracts or by chromium ions, used in mineral tanning. In Ancient Egypt, the vegetable tanning (hydrolysable tannins (pyrogallols) was employed, and is based on the treatment of animal hides using natural sources of tannins such as oak wood, gulls and sumac leaves, as well as condensed tannins (catechols) found in acacia, mimosa and pine. Vegetable tannins are large molecules, which interacts and transforms animal leather proteins (collagen) into resistant insoluble products which are chemically stable. These products may have different chemical structures, but it has some common properties such as they are insoluble in organic liquids, miscible with water, hygroscopic, amorphous substances, very sensitive to oxidation and reduction (Puică et al. 2006).Collagen-based artifacts include leather, parchment and vellum. Although the total manufacturing process of the three types differs, some manufacture steps are the same. The chemical and physical properties of leather vary significantly from those of parchment; indeed the stability of leather is increased due to the bonding of the fiber network taking place during the tanning process. Many Egyptian leather products have often been preserved intact, thus allowing a much better knowledge of the manufacturing techniques and stages, such as salting, tanning, lubrication and finishing.
