Science Fair Project Encyclopedia
Leather is a material created through the tanning of hides, pelts and skins of animals, primarily cows. Leather was a very important clothing material, and its other uses were legion. Together with wood, leather formed the basis of much ancient technology. Leather with the fur still attached is simply called fur.
Forms of leather
There are a number of processes whereby the flesh of a dead animal can be formed into a supple, strong material commonly called leather.
- Vegetable-tanned leather is tanned using tannin (hence the name "tanning") and other ingredients found in vegetable matter -- tree bark, and other such sources. It is supple and brown in color, with the exact shade depending on the mix of chemicals and the color of the flesh. Vegetable-tanned leather is not stable in water; it tends to discolor, and if left to soak and then dry it will shrink and become less supple and harder. In hot water, it will shrink drastically and plasticize, becoming a rigid, brittle material of little use.
- Chrome-tanned leather, invented in 1858, is tanned using chromium sulfate and other salts of chromium. It is more supple and stretchier than vegetable-tanned leather, and does not discolor or lose shape as drastically in water as vegetable-tanned. More esoteric colors are possible using chrome tanning.
- Alum-tanned leather is tanned using aluminum salts mixed with a variety of binders and protein sources, such as flour, egg yolk, etc. Purists argue that alum-tanned leather is technically "tawed" and not tanned, as the resulting material will rot in water. Very light shades of leather are possible using this process, but the resulting material is not as supple as vegetable-tanned leather.
- Rawhide is made by scraping the skin thin, soaking it in lime, and then stretching it while it dries. Like alum-tanning, rawhide is not technically "leather", but is usually lumped in with the other forms. Rawhide is stiffer and more brittle than other forms of leather, and is primarily found in uses such as drum heads where it does not need to flex significantly; it is also cut up into cords for use in lacing or stitching.
Leather -- usually vegetable-tanned leather -- can be oiled to improve its water resistance. This supplements the natural oils remaining in the leather itself, which can be washed out through repeated exposure to water. Frequent oiling of leather, with mink oil or a similar material, keeps it supple and improves its lifespan dramatically.
In general, leather is sold in three forms:
- Full-Grain leather, made from the finest raw material, are clean natural hides which have not been sanded to remove imperfections. Only the hair has been removed. The grain remains in its natural state which will allow the best fiber strength, resulting in greater durability. The natural grain also has natural breathability, resulting in greater comfort. The natural Full-Grain surface will wear better than other leather. Rather than wearing out, it will develop a natural "Patina" and grow more beautiful each passing year. The finest furniture, and footwear are made from Full Grain leather.
- Corrected-Grain Leather. Corrected Leather is fuzzy on one side and smooth on the other. The smooth side is the side where the hair and natural grain used to be. The hides, which are made from inferior quality raw materials, have all of the natural grain sanded off, and an artificial grain applied. Top grain leather must be heavily painted to cover up the sanding and stamping process. It is actually more similar to vinyl than it is to leather.
- Suede, is the interior split of the hide. It is "fuzzy" on both sides. Suede is less durable than top-grain.
Suede is cheaper because many pieces of suede can be split from a single thickness of hide, whereas only one piece of top-grain can be made. However, as the look of full-grain is in demand, manufacturers use a variety of techniques to make suede appear to be full-grain. For example, in one process, glue is mixed with one side of the suede, which is then pressed through rollers; these flatten and even out one side of the material, giving it the smooth appearance of full-grain.
Leather is sold in a variety of thicknesses. Top-grain thicknesses, called weights, are categorized by ounce ranges, as in "7-8 oz" or "3-4 oz". Derived from the weight per square foot, these measures actually refer to the thickness of the piece of leather; each "oz" is approximately 1/64th of an inch of thickness. Hence, 7-8oz leather is roughly 8/64ths or 1/8th of an inch thick. The weight is usually given as a range, as above, because the inherent variability of the material makes ensuring a precise thickness very difficult. Some leather manufacturers report leather thickness in millimeters; 3-4 oz leather is roughly equivalent to 1.3mm leather.
Leather from other animals
Today, most leather is made of cow hides, but many exceptions exist. Lamb and deer skin are used for soft leather in more expensive apparels. Kangaroo leather is used to make items which need to be strong but flexible, such as motorcycle gloves. Leather made from more exotic skins has at different times in history been considered very beautiful. For this reason certain snakes and crocodiles have been hunted to near extinction.
In the 1990s, farming of ostriches and emus for their meat became popular. As a side product, ostrich leather became a fad for a while. Ostrich leather has a characteristic "goose bump" look because of the large follicles from which the feathers grew.
In Thailand, sting ray leather is used in wallets and belts in the same way as regular cow leather. Sting ray leather is as tough and durable as hard plastic - even a metal file cannot leave a scratch. The leather is often dyed black and covered with tiny round bumps in the natural pattern of the back ridge of an animal. These bumps are then usually dyed white to highlight the decoration.
Working with leather
Leather can be decorated by a variety of methods, including:
- leather dying
- leather painting
- leather carving
- leather stamping
- leather embossing
Leather in modern culture
Leather, due to its excellent abrasion and wind resistance, found a use in rugged occupations. The enduring image of a cowboy in leather chaps gave way to the leather-jacketed and leather-helmeted aviator. When motorcycles were invented, some riders took to wearing heavy leather jackets to protect from road rash and wind blast; some also wear chaps or full leather pants to protect the lower body.
Leather fetishism is the name popularly used to describe a fetishistic attraction to people wearing leather, or in certain cases, to the garments themselves. There is a thriving Leather subculture in lesbian, gay male, bisexual, transgender, and queer BDSM culture.
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