tanning - Modern methods of tanning, Ancient methods of tanning, Another use

The process of turning raw animal hide or skin into a permanent, durable, flexible form. Cleaned skin is soaked in solutions of vegetable extracts containing tannins (eg oak bark) or, since the 19th-c, chrome salts.

Tanning is the process of converting putrescible skin into non-putrescible leather, usually with tannin, an acidic chemical compound that prevents decomposition and often imparts color.

Modern methods of tanning

The first stage is the preparation for tanning. The second stage is the actual tanning and other chemical treatment.

Preparing hides begins by curing them with salt. The hides are then soaked in clean water to remove the salt and a lime/water solution to loosen the hair.

Tanning can be performed with either vegetable or mineral methods. Before tanning, the skins are unhaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days.

Vegetable tanning uses tannin, from which tanning gets it name. Vegetable tanned hide is flexible and is used for luggage and furniture.

Mineral tanning usually uses chrome. 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. (Encarta, 2003)

Depending on the finish desired, the hide may be waxed, rolled, lubricated, injected with oil, split, shaved and, of course, dyed.

Ancient methods of tanning

In ancient history, tanning was considered a noxious trade and relegated to the outskirts of town, amongst the poor. Indeed, tanning by ancient methods is so foul smelling that tanneries are still isolated from those towns today where the old methods are used.

Tanners would take an animal skin and soak it in water. Next, either they soaked the skin in urine to loosen hair fibers or they let the skin putrefy for several months, after which they dipped the skin in a salt solution.

Once the hair was removed, tanners would bate the material by pounding dung into the skin or soaking the skin in a solution of animal brains. They would also take cedar oil, alum, or tannin and stretch the skin as it lost moisture and absorbed the tanning agent.

Variations of these methods are still used by do-it-yourself outdoorsmen to tan hides. The use of brains and the idea that each animal has just enough brains for the tanning process have led to the saying, "Every animal has just enough brains to preserve its own hide, dead or alive."

Another use

The term tanning is also used metaphorically for a hiding in the sense of severe physical punishment which leaves clear marks (reddening, stripes, or even scars) on the beaten skin.