WHAT IS LEATHER?
THINGS TO KNOW ABOUT Leather: is a durable and flexible material created by tanning animal rawhide and skins. The most common raw material is cattle hide. It can be produced at manufacturing scales ranging from artisan to modern industrial scale. Leather is used to make a variety of articles, including footwear, automobile seats, clothing, bags, book bindings, fashion accessories, and furniture. It is produced in a wide variety of types and styles and decorated by a wide range of techniques. The earliest record of leather artifacts dates back to 2200 BC.
Leather usage has come under criticism in the 20th and 21st centuries by animal-rights groups (e.g. PETA). These groups claim that buying or wearing leather is unethical because producing leather requires animals to be killed.
History Of Leather
A lot of us today really love wearing leather. Seems like almost everyone loves the smell of good leather but few of us know about leather. Do you know the kind of leather you are wearing? What state, country or even what kind of animal that the leather you are wearing comes from?
The manufacture of leather predates recorded history. There is evidence that some leather samples found in Northern Germany may have been produced perhaps 12,000 years ago.
A protective, hard-wearing layer of keratineous cells, which, although of varying thickness over the body of the animal, is very thin compared with the underlying DERMIS .
The grain layer or dermal surface
The juncture between the grain layer and the dermis or cerium
The major portion of the skin (the DERMIS or cerium), which is the part converted into leather.
Before tannage, the approximate composition of a freshly flayed hide is Water 64 %
Protein 33 %
Fats 2 %
Mineral salts 0.5%
Other substances (pigments, etc.) 0.5%
The 33% which is protein consists of:
Structural proteins, or Elastin (yellow fiber woven in the collagen fiber) 0.3%
Collagen (which tans to give leather) 29%
Keratin (protein of the hair and epidermis) 2%
Non-structural proteins, or Albumen or globulin’s (soluble, non-fibrous proteins) 1 %
Mucins or mucoids (mucous materials associated with fibers) .7%
Tanning processes largely differ in which chemicals are used in the tanning liquor. Some common types include:
- Vegetable-tanned leather is tanned using tannin’s extracted from vegetable matter, such as tree bark prepared in bark mills. It is the oldest known method. It is supple and light brown in color, with the exact shade depending on the mix of materials and the color of the skin. it tends to discolor, and if left to soak and then dry, it shrinks and becomes harder in water, a feature of vegetable-tanned leather that is exploited in traditional shoe-making.
- Chrome-tanned leather, invented in 1858, is tanned using chromium sulfate and other chromium salts. It is also known as “wet blue” for the pale blue color of the un-dyed leather. The chrome tanning method usually takes approximately one day to complete, making it best suited for large-scale industrial use. It is more supple and pliable than vegetable-tanned leather and does not discolor or lose shape as drastically in water as vegetable-tanned.
- Aldehyde-tanned leather is tanned using glutaraldehyde or oxazolidine compounds. It is referred to as “wet white” due to its pale cream color. It is the main type of “chrome-free” leather, often seen in shoes for infants and automobiles. Formaldehyde has been used for tanning in the past; it is being phased out due to danger to workers and sensitivity of many people to formaldehyde.
- Chamois leather is a form of aldehyde tanning that produces a porous and highly water-absorbent leather. Chamois leather is made using marine oils (traditionally cod oil) that oxidize to produce the aldehydes that tan the leather.
- Brain tanned leathers are made by a labor-intensive process that uses emulsified oils, often those of animal brains such as deer, cattle, and buffalo. They are known for their exceptional softness and wash ability.
- Alum leather is transformed using aluminum salts mixed with a variety of binders and protein sources, such as flour and egg yolk. Alum leather is not actually tanned; rather the process is called “tawing”, and the resulting material reverts to rawhide if soaked in water long enough to remove the alum salts.
In general, leather is produced in the following grades:
- Top-grain leather includes the outer layer of the hide, known as the grain, which features finer, more densely packed fibers, resulting in strength and durability. Depending on thickness, it may also contain some of the more fibrous under layer, known as the corium. Types of top-grain leather include:
- Full-grain leather contains the entire grain layer, without any removal of the surface. Rather than wearing out, it develops a patina during its useful lifetime. It is usually considered the highest quality leather. Furniture and footwear are often made from full-grain leather. Full-grain leather is typically finished with a soluble aniline dye. Russia leather is a form of full-grain leather.
- Corrected grain leather has the surface subjected to finishing treatments to create a more uniform appearance. This usually involves buffing or sanding away flaws in the grain, then dyeing and embossing the surface.
- Nubuck is top-grain leather that has been sanded or buffed on the grain side to give a slight nap of short protein fibers, producing a velvet-like surface.
- Split leather is created from the corium left once the top-grain has been separated from the hide, known as the drop split. In thicker hides, the drop split can be further split into a middle split and a flesh split.
- Bicast leather is split leather that has a polyurethane or vinyl layer applied to the surface and embossed to give it the appearance of a grain. It is slightly stiffer than top-grain leather but has a more consistent texture.
- Patent leather is leather that has been given a high-gloss finish by the addition of a coating. Dating to the late 1700 s, it became widely popular after inventor Seth Boyden developed the first mass-production process, using a linseed-oil-based lacquer, in 1818. Modern versions are usually a form of bi-cast leather.
- Suede is made from the underside of a split to create a soft, napped finish. It is often made from younger or smaller animals, as the skins of adults often result in a coarse, shaggy nap.
- Bonded leather, also called reconstituted leather, is a material that uses leather scraps that are shredded and bonded together with polyurethane or latex onto a fiber mesh. The amount of leather fibers in the mix varies from 10% to 90%, affecting the properties of the product.
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