Mineral Tanning
Prior to the introduction of the basic chromium species in tanning, several steps are required to produce a tannable hide. These steps include scudding, or removing the hair, liming, or the introduction of alkali agents such as sodium hydroxide, deliming, or restoring neutral pH, bating, or softening the skin with enzymes, and pickling, or lowering pH of the hide with salt and sulfuric acid. The pH is very acidic when the chromium is introduced to ensure that the chromium complexes are small enough to fit in between the fibers and residues of the collagen. Once the desired level of penetration of chrome into the substance is achieved,the pH of the material is raised again to facilitate the process. This step is known as "basification". In the raw state chrome tanned skins are blue and therefore referred to as "wet blue." Chrome tanning is faster than vegetable tanning (less than a day for this part of the process) and produces a stretchable leather which is excellent for use in handbags and garments.
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