Bating
]Bating is a technical term used in the tanning industry to denote leather treated with hen or pigeon manure, similar to puering (see puer), where the leather was treated with dog excrement. In both cases, this treatment was performed on raw hide before tanning to make the skins and the resulting leather soft and supple. Today, both practices are obsolete and have been replaced in tanneries by other natural proteolytic enzymes.
Leather processing
Since ancient times, tanners have used dog feces or hen and pigeon manure in the early stages of leather treatment to create soft leather. A bath solution containing these animal extracts was prepared, into which the raw hide was placed for a few days. This activated the bacteria and enzymes that interacted with the collagen in the animal skin, making the leather soft and supple. This step was followed by drenching, a term describing skins that were thoroughly washed in a bath solution of bran (usually barley or rye) or ash bark. This process was believed to open up the fibers, and if lime (CaO) was used to remove hair before the actual bating, drenching helped eliminate excess or residual lime trapped in the leather.
Early inventors focused on tanning viewed bating merely as a method for removing lime from the skins. Since the use of animal feces was repulsive, they sought substitutes by inventing artificial bates. However, they overlooked that bating also affects the skin fibers, making portions of the skins soluble and achieving the desired condition. One early invention aimed at replicating bating involved using old lime liquors (high in ammonia) neutralized with sulfuric acid. This method closely approximated the conditions created by dung.
Experimentation and Research
Puering fell out of favor after Robert Hasenclever began producing the enzyme pancreatin on an industrial scale between 1895 and 1897. By 1907, Otto Röhm was using it in tanneries. J.T. Wood, while investigating the microbial properties of dog feces, was able to isolate different bacterial species and found that aged dog feces was more potent (and therefore more effective) than fresh dog feces. The bacteria that settle on the excrement release, under the right conditions, the principal enzyme trypsin.
Natural Bates
Primitive tanning methods varied from country to country, but the use of puering and bating was not widespread, as tanners shifted to vegetable tanning, achieving nearly the same results. In Western societies, modern tanning techniques aimed to replicate the effects of puering and bating by using a natural bate. Papain, the active proteolytic enzyme found in latex harvested from the skin of the papaya fruit (Carica papaya), is believed to replicate the action of traditional puering and bating. The protein-digesting enzyme is now extensively used in the leather industry, following the dehairing of the animal skin, usually with lime and other proteolytic enzymes, then the deliming of the hide with mineral acid. This process is thought to release traces of lime still trapped in the hide after deliming, as well as remove unwanted grease and aid in the subsequent tanning process by altering proteins.
Today, in the modern tanning industry, where nearly all innovations have come from substituting vegetable tanning agents with chemical ones, bating remains the only step in leather processing where chemicals cannot replace enzymatic processes, as bating imparts certain desired characteristics to the finished leather. The large-scale use of microbial enzymes, following the introduction of fermentation technology, has become standard in the tanning industry.
Enzymatic soaking of raw hides has been shown to loosen the scud, initiate the opening of the fiber structure, and produce a leather product with less wrinkled grain when used at an alkaline pH of less than 10.5. In rabbit skins, it improves softness and elasticity, increasing the surface area yield of the fur by 3.3%. Bating also hydrolyzes casein, elastin, albumin, globulin-like proteins, and non-structural proteins that are not essential for leather making.
Primitive Practices
One of the earliest references to puering is found in the old rabbinic Minor tractate, Kallah Rabbati (end of chapter 7): "What is the reason that dogs were privileged to have books of the Law and doorpost scripts prepared from their excrement? It is because it says [of them]: 'not a dog shall bark against any of the people of Israel' (Exo. 11:7)." A record of primitive tanning from the 12th century by Abraham ben Isaac of Narbonne (1085–1158) mentions the tanning method employed in his time in southern France, where puering was still practiced after the hairs of the animal were removed with lime in preparation for writing a Torah scroll, making the hide stiff again:
"After taking dry [sheep] skins whose wool had been soaked [in lime water for removal], they leave them in the water until they become soft [=soaking]. Then they place them inside a pit designed for this purpose, adding a little dog feces, with no prescribed quantity [=puering], and a bit of salt, sealing the mouth of the pit. They leave it for one day in summer months and three days in winter months, no longer, to prevent spoilage. They then remove them and check for holes; if a hole is found, they sew it up. Then they lay the skins over a wooden frame prepared for this purpose and rinse them thoroughly with running water [=drenching]. Afterward, they prepare a heaping batch of gallnuts, pounding or grinding them thoroughly. They then apply three liters of the Baghdad measure to each leather sheet, covering both sides with gallnuts, sprinkling a little water over them. They apply more gallnuts on the grain layer—where the hairs once were—than on the flesh side, doing the same with each sheet. The application is made twice daily, and on the third application, they once more plaster with remaining gallnuts onto the leather and lay it out in the sun until it whitens, leaving it until it dries [=tanning]. They then shake off excess gallnuts and cut the leather.
Tanners in Egypt in the 12th century and those in late Yemen employed different methods to varying extents, yet without puering or bating, and without gallnuts. Rather, after soaking and fleshing, they utilized tannins found in the ground leaves and crushed tender stems of Acacia (Acacia etbaica and Acacia nilotica kraussiana), with which a bath solution was made, inserting raw hides and leaving them for about two weeks, constantly stirring and changing the water after one week. In some places in Yemen, the leaves of African rue (Peganum harmala) replaced Acacia leaves. In Yemen and Ethiopia, some tanners applied castor-bean oil from the castor plant (Ricinus communis) to the finished leather product, adding additional softness and suppleness to the leather.]\]
Leather production processes:
External links
- More information is available at [ Wikipedia:Bating ]
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