Leather is produced by a process called tanning , the following is a brief description of what is involved . Implement suppliers may be aware of this information , but judging by some advertising , many are not .
WHAT IS TANNING
Leather is made from animal skins or hides which have been chemically treated to preserve quality and natural beauty. The chemical procedure used to ready raw animal hides for use is called “tanning.” A piece of hide or skin which has been tanned produces a strong, flexible leather which is able to resist decay and spoilage.
The majority of leather made today is produced from tanned cattle hides, though many types of hides can be used, including those from horses, pigs, goats, calves, labs, deer, kangaroos, reptiles, seals, and walrus.
STAGES OF TANNING
Raw animal skins go through several steps during the tanning process. Depending on the type of hide used and the desired end-product, the steps taken during tanning can vary greatly.
Animal skins or hides are first “cured,” a process which involves salting and/or drying the hide once it’s been stripped from the animal. Because this step needs to be performed almost immediately upon removal from the animal, it often takes place inside the meat-packing industry or at a nearby factory. Hides can be cured in one of two ways:
Wet-Salting is done by salting the hide and then piling many skins together until they form a moist bunch. They are then left to cure for one month, so that the salt can completely be absorbed into the skin.
Brine-curing is more common than wet-salting, as it’s considered a faster, easier method. During brine curing, hides are positioned carefully in vats and smothered with a mixture of salt and disinfectant. After 10-16 hours, the skins are completely cured and ready to move on to the next stage.
Once the hides have been cured, they are then soaked in water for several hours to several days. The water helps to rid the skin of salt, dirt, debris, blood and excess animal fats.
After soaking, animal hides are moved through a machine which strips the flesh from the surface of the hide.
The hides are then transported to a large vat, where they are immersed in a mixture of lime and water, which loosens the hair from the skin. After a 1-10 day soak, the hair is mechanically removed from the hide.
Stray hairs and fat which were missed by machine, are removed from the hide with a plastic tool or dull knife in a process known as “scudding.” Scudding is done by hand.
After the hair and debris has been cleaned from the skin, hides are delimed in a vat of acid. After the lime has been pulled from the skin, hides are treated with enzymes, which smooth the grain of the leather and help to make the resulting product soft and flexible.
Hides and skins are often treated several times during the process of tanning. Which type of tanning procedure is used, depends largely on the hide itself and the resulting product intended.
Hides which have been tanned with a vegetable tanning agent solution produce flexible, but stiff leathers, such as those used in luggage, furniture, leashes, belts, hats, and harnesses.
Vegetable tanning consists of stringing hides on large frames, located inside large vats, and exposing them to tannin, a natural product found in the bark, wood, leaves and fruits of chestnut, oak and hemlock trees. Hides are transferred to many different bins during this step, each containing a stronger solution of tannin. Vegetable tanning prevents the skin from decay and shrinkage.
Mineral or chrome tanning is performed on skins which will be used for softer, stretchier leathers, such as those found in purses, bags, briefcases, shoes, gloves, boots, jackets, pants, and sandals.
Hides which are tanned with minerals are pickled first in an acid and salt mixture. From there, hides are soaked into a chromium-sulfate solution. This process is much faster than vegetable tanning, and is usually a 1-day project.
Depending on the desired product, the hides then go through a dyeing process, which also involves adding moisture back into the skin. Hides which have been vegetable tanned are bleached and them soaked with oils, soaps, greases and waxes to make them more pliable.
Rolling leather running the skins through a machine, which works to firm the leather to make it stronger.
After the rolling process has finished, leathers are stretched, where they dry out in a heat controlled room.
The final step in the tanning process involves finishing the skin. This is done by covering the grain surface with a chemical compound and then brushing it. Light leathers are buffed and sandpapered to cover imperfections. Leathers which are buffed for long periods of time become suede.
Waxes, pigments, dyes, glazes, oils, waxes and other solutions are also added to make the leather more appealing to the buyer.