Curing is employed to check putrifaction of the protein substance (Collagen) because of the chance of bacterial infection due to the time lag that might occur from procuring it to processing it. Preparing hides begins by curing them with salt. The fourth stage is used to apply finishing material to the surface or finish the surface without the application of any chemicals if so desired. The third stage applies retanning agents and dyes to the material to provide the physical strength and properties desired depending on the end product. The second stage is the actual tanning and other chemical treatment. The first stage is the preparation for tanning. The use of brains and the idea that each animal (except buffalo) 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." Variations of these methods are still used by do-it-yourself outdoorsmen to tan hides. The mixture would then be placed over a fire to boil off the water to produce hide glue. Tanners would place scraps of hides in a vat of water and let them deteriorate for months. Leftover leather would be turned into glue. As the skin was stretched, it would lose moisture and absorb the agent. In some variations of the process, cedar oil, alum or tannin were applied to the skin as a tanning agent. Also common were "piss-pots" located on street corners, where human urine could be collected for use in tanneries or by washerwomen. It was this combination of urine, animal feces and decaying flesh that made ancient tanneries so odiferous.Ĭhildren employed as dung gatherers were a common sight in ancient cities. The ancient tanner might use his bare feet to knead the skins in the dung water, and the kneading could last two or three hours. Sometimes the dung was mixed with water in a large vat, and the prepared skins were kneaded in the dung water until they became supple, but not too soft. Among the kinds of dung commonly used were that of dogs or pigeons. Once the hair was removed, the tanners would bate the material (see below) by pounding dung into the skin or soaking the skin in a solution of animal brains. After the hair fibers were loosened, the tanners scraped them off with a knife. This was done by either soaking the skin in urine, painting it with an alkaline lime mixture, or simply letting the skin putrefy for several months then dipping it in a salt solution. Next, the tanner needed to remove the hair fibers from the skin. Then they would pound and scour the skin to remove any remaining flesh and fat. ![]() First, the ancient tanners would soak the skins in water to clean and soften them. Skins typically arrived at the tannery dried stiff and dirty with soil and gore. Around 2500 BC, the Sumerians began using leather, affixed by copper studs, on chariot wheels. The ancients used leather for waterskins, bags, harnesses, boats, armor, quivers, scabbards, boots and sandals. Indeed, tanning by ancient methods is so foul smelling that tanneries are still isolated from those towns today where the old methods are used. Based on a newly developed analytical method for monitoring the tanning success via the ion content in the tanning liquid the process principle and the acceleration of the tanning process is proven and demonstrated.In ancient history, tanning was considered a noxious or "odiferous trade" and relegated to the outskirts of town, amongst the poor. ![]() it is shown that the same tanning result is obtained in only 5 h if the process is performed under CO2-pressure between 30 and 100 bar. Typically, about 30 h are used to tan skins with chrome. This article focuses on the reduction of time of the process for the tanning step. Compressed carbon dioxide can be used to shorten tanning times, to reduce water effluents and pollution and to save leather-finishing-fats. Several steps of the tanning process can be intensified by high-pressure technology. The leather producing industry transforms untreated hides that may rot under wet conditions and are brittle under dry conditions into durable, imperishable leather by processes which incorporate tanning agents into the hides.
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