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Leather Types and Terms
- Garment Leather – A light weight soft leather ranging from 2-5 oz.
- Chap Leather – A heavier leather than garment leather, heavier duty ranging from 4-5 oz.
- Upholstery Leather – Comparable to garment leather but on the heavier side from 3-5 oz.
- Oil Tanned – A versatile, water/fluid repelling, sturdy leather ranging from 3-5oz.
- Latigo – Heavy duty firm leather ranging from 4-10 oz.
- Deer or Elk skin – Very soft and supple lightweight leather with grain or suede from 2.5-4 oz.
- “Distressed” Leather – Leather finish that gives the grain side an antique or “used” look.
- Suede Splits – The inside piece of a thicker piece of leather with suede on both sides from 2-5oz.
- Patent Leather – Leather that has a hard and glossy finish (This used to be a patented process, hence the name)
- Glazed – Another form of finishing that produces a hard glossy finish.
- Alligator Grain – A faux alligator embossing on leather to make it look like alligator hide.
- Ostrich Grain – A faux ostrich embossing on leather to make it look like ostrich hide.
- Lace or Thong – Leather that is cut into thin strips that can vary in width for a variety of uses.
- Sinew – A string made of shredded fibers of animal tendon.
- Artificial Sinew – A man made sinew substitute.
- Waxed Linen Thread – Linen thread that has had wax applied during manufacture.
Here we will try to explain the basics of different leather tanning processes for informational purposes with regards to the materials we use.
Leather tanning is a multi-staged process of preserving an animal hide or pelt so as to make is useful for many different purposes. Tanning will prevent hides from the normal decaying process that happens to dead animal flesh, keep the hide supple and durable and water/fluid resistant.
The surface of the hide or grain side contains hair and oil follicles and is smooth, roughed up to be a suede or sometimes the hair is left intact. The flesh side is thicker and softer.
The most common hides used in leather manufacturing are from cattle, sheep and pigs. Other exotic leathers include: kangaroo, stingray, shark, horse, and buffalo to name a few.
Tanning is a reaction of the collagen fibers in the hide with preserving chemicals and oils in several steps usually with a drying or resting period between processes. Leather may be tanned mechanically (mass produced) or “by hand” the old fashioned way. Obviously the mechanical means is less time and energy consuming but yields more waste products than the old fashioned way. Tannins which are of plant origin is where we get the name “tanning” from. Other chemicals include salts, chromium, alum, syn-tans (synthetic chemicals), formaldehyde, glutaraldehyde and heavy oils.
Most hides are preserved in salt or brine solutions before the actual tanning process begins. Salts kill bacteria, fungi and have been used for years to preserve food and other animal products.
The Tanning Process Briefly Explained
The first step in any tanning process is to remove the salt or brine by soaking. This also restores moisture to the hide and helps to remove fats and flesh that may be left on the hide. After the salts are removed, hides will be scraped to a uniform thickness and excess fat and flesh will be removed. The hair removing process will begin next (unless the hair is to remain on the leather). Hair removal is done by several different methods, liming being the most common. Other methods of hair removal include thermal, oxidative and chemical methods. After the liming or other chemical treatment, hair is removed by scraping by hand or machine. After liming hides are treated to remove the lime and enzymes are used to soften the leather and make it more flexible. Hides may be treated with a salt pickling for further preservation.
Vegetable Tanning or Vegtan
This process involves soaking hides in increasing concentrations of vegetable or plant tannins. The most common source of these tannins is from the bark of certain trees, among them are oak, hemlock, alder, chestnut oak, birch, willow and fir. Other barks are used for different results. Each one will add a different color or characteristic to the leather and often more than one type is used. Also, dung (excrement) usually from dogs or pigeons can be used. Human urine has also been used in the tanning process as well as brains or decaying animal flesh. The hide will be treated and stretched several times to allow the tannins to soak through the hide. The stretching process opens up the hide to allow moisture to escape while letting the tannins in. Another method involves kneading or agitating the leather either by hand, stomping on it in a vat like you would to extract juice from grapes or by mechanical means while it is soaking in the tannin solution. Also, hides can be stacked in pits layered with tree barks or dung or a mixture of the two, covered and kept wet for a period of time until the tannins are absorbed into the hides.
After the hides have sufficiently absorbed the tannins they are set out to smooth and dry. Drying may be by several different methods, the simplest being air drying where the hide is hung or racked and air is allowed to naturally circulate around it. Other methods include mechanical means where heat, circulated air, vacuuming or electromagnetic fields are used to dry the leather.
Chrome tanning is the method used for most mass produced lightweight leathers. Advantages of chrome tanned leather include softness, pliability, heat resistance and water stability. Chrome tanning is science of attaining a certain pH in the pickled leather and adding it to a chromium salt bath and raising the pH After this chrome bath, hides will have excess liquid removed and be graded according to their thickness and qualities. They may go through further processing including splitting (cutting the grain side from the flesh side in order to make two or more pieces) and shaving for a desired thickness or weight. Leather is then sent to a dying process to introduce color. Some leather may be dyed on the surface only, while others are dyed partially or completely through the leather. Fat-liquoring is the next step which introduces oils back into the leather which are lost in the previous tanning processes. This is an important step to preserve the softness, pliability and water resistance of the leather.
All leather will pass through one or more finishing processes after it is dried. Finishing processes include buffing with abrasives to give a suede finish, dying for colors, waxing or oiling for water or fluid resistance, shellacs and lacquers for gloss and shine. Leather may also be embossed at this time. After finishing the leather is ready for whatever the leather craftsman has decided to create out of it.
Leather is sold by weight. You will see leather referred to in approximate ounces per square foot. Weight of leather depends on several different factors, mainly the type of leather (cow, pig, sheep, buffalo, etc.), the tanning and finishing processes and the thickness. A piece of buffalo skin leather that has been chrome tanned could be lighter in weight than a cow hide latigo of similar thickness because of the extra oils and waxes in the latigo. Generally an ounce of weight is equal to 1/64” in thickness. Because of slight variances in the thickness of the finished leather, they are advertised with a weight range. The weight range is used to gauge the approximate thickness of the leather. A U.S. quarter dollar is equal in thickness to 4 oz. leather.