Vegetable tanning is based on tannins (polyphenols and gallic acid) which are found naturally in plant species. Tanning with plant substances has existed for over 5,000 years and was, for many centuries, the main tanning method. As these tannins are derived from plants, the leather is called vegetable-tanned leather. These substances are placed in a pit along with the skins and hides. Among all, the most commonly used are leaves, bark, galls, sawdust, olive leaves, rhubarb roots or mimosa. Vegetable tanning uses tannins (a class of polyphenol astringent chemicals), which occur naturally from plants. The three most widely used tanning agents are vegetable tannin, mineral salts such as chromium sulfate, and fish or animal oil. The transition to leather requires permanent incorporation of chemical species into the collagen network however, until the twentieth century, few tanning chemistries were known and applied by fellmongers. Technically speaking, an increase in shrinking/ denaturation temperature also accompanies the transformation of skin in leather, measured as resistance to wet heat (hydrothermal resistance). The first feature is an outstanding resistance to putrefaction (it is common knowledge that some leather artifacts dated back to thousands years ago are still preserved) in a more general perspective a tanned skin is awaited to be softer than it was in the raw state, often with a typical color and smell all the changes given by tanning should be permanent. Once a skin is tanned some typical properties are expected to appear. Historically this process was considered a noxious or “odoriferous trade” and relegated to the outskirts of town.Īt the end of beam house operations, the main component of hides is structured collagen, that is ready to be transformed into leather. Tanning hide into leather involves a process which permanently alters the protein structure of skin, making it more durable and less susceptible to decomposition, and also possibly coloring it.īefore tanning, the skins are dehaired, degreased, desalted and soaked in water over a period of six hours to two days. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name. A tannery is the place where the skins are processed. A tanning agent displaces water from the interstices between the protein fibers and cements these fibers together. Tanning is the process of treating skins and hides of animalsto produce leather.
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