Natural skin tanning

Leather. Natural leather is made from hides, which are salted and cured, then taimed. Through the preparing process, useless matter which caimot be taimed, such as outerskin (epidermis) and flesh, are removed, leaving the tme skin (corium). In the tanning process, the fluid matter which maintains the skin in a flexible and moist condition is removed, and there remains nothing but the fibrous portion to be acted on by the tanning chemicals (1-3). 

Potassium alum, which also occurs naturally as the mineral kalinite [7784-24-9], KAl(SO 2 12H20, sp gr 1.75, is used ia tanning skins, as a mordant ia dyeiag, and ia the pharmaceutical and cosmetic iadustries (see Pharmaceuticals Cosmetics). It is used as a styptic pencil and as a hardening agent and set accelerator for cement and plaster. The ACGIH threshold limit value TWA is 2 mgAl/m (1 ). 

There has always been an abundance of natural fibers and elastomers, but few plastics. Of course, early humans employed a crude plastic art in tanning the protein in animal skins to make leather and in heat-formed tortoise shells. They also used naturally occurring tars as caulking materials and extracted shellac from the excrement of small coccid insects Coccus laced). 

In Ancient Egypt, there were some recipes for the treahnent of bums either in the critical phase or in the cicatricial phase and particularly a recipe to treat the ugly depigmentation of naturally tanned skins, daily exposed to a strong sun. 

Realgar is employed as a depilatory in tanning, its red colour being a desirable feature in the treatment of hides and skins. It has been used as a paint pigment under the name of arsenic orange, but it is not too permanent and is now seldom used. Its early use as a remedy for asthma, etc., has been mentioned (p. 23). Unless carefully prepared, the commercial product is liable to contain white arsenic, and the poisonous nature of the latter tends to limit the applications of realgar. 

Naturally white, but slightly yellowed fur skins from sheep and lambs are reduction bleached, most commonly with dithionite or/and in combination with hydrogen peroxide in a weakly alkaline medium. A true bleach in the sense of destroying the natural pigments in the hair can only be achieved by means of oxidation with, e g., hydrogen peroxide, catalyzed by iron(n) salts. This exothermic process is very difficult to control and must be monitored carefully. In addition, the skin must not be chrome tanned, as this could cause serious damage. 

Muscle and organ tissue make up most of what is referred to as meat. These materials are composed mostly of proteins and water, and they begin decomposing immediately after the animal s death. These tissues are removed from skin during tanning or taxidermy, although dried remnants may remain. In traditional natural history collections, these materials are usually wet preserved in 70% ethanol as part of whole or partial animals. 

The conversion of animal hides into leather by treatment with water-soluble plant extractives has been practiced since antiquity. This process became known as tanning and obviously involved the reaction of a naturally occurring extractive, tannin, with the protein in the hide. We now know, of course, that tannins comprise a whole spectrum of chemical compounds, but generally they are polyphenolic and polymeric. Tannins have been isolated from a wide variety of raw materials, including insect galls, fruit skins, seed hulls, leaves, bark, and heartwood. Indeed, tannins are of nearly ubiquitous occurrence in higher orders... 

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