Oil Tanned Leather
Tanning is the process of treating skins of animals to produce leather, which is more durable and less susceptible to decomposition.
Tanning leather involves a process which permanently alters the protein structure of skin. Making “rawhide” (untanned but worked hide) does not require the use of tannin. Rawhide is made by removing the flesh and fat and then the hair by use of an aqueous solution (this process is often called “liming” when using lime and water or “bucking” when using wood ash (lye) and water), then scraping over a beam with a somewhat dull knife, then drying. The two aforementioned solutions for removing the hair also act to clean the fiber network of the skin and allow penetration and action of the tanning agent, so that all the steps in preparation of rawhide except drying are often preludes to the more complex process of tanning and production of leather. Before tanning, the skins are unhaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days.1
To accommodate this, old tanning agents, such as alum and salts were replaced by newer chemicals.
Chromium tanning was invented in the 1800’s, which enabled a shorter time in the entire process. In addition, instead of using clay lined pits, the tanners began using rotating drums. The drums allowed the hide to be subjected to the actual ‘tanning’ step of the process more thoroughly and quicker. 2
Leather tanning is without a doubt one of the oldest human activities. In the beginning, skins obtained from hunting and livestock breeding could be used for clothing or tents, but they became stiff at low temperatures, while they rotted with heat. It was probably then that attempts were made to render them more flexible and stronger by rubbing in animal fats; the first rudimental tanning process is mentioned in Assyrian texts and in Homers Iliad.3
The name of tan is applied to coarsely powdered bark which is obtained mostly from oak and hemlock trees, although all barks contain more or less tannin, and in some countries the extract of others is used. To tan a skin is to saturate it with tannin in such a manner as to promote the slow combination of this principle with the gelatine, albumen, and fibrine contained in the former.4
Tanning is a general term used for the process of converting animal skins to finished leather. Animal hides and skins absorb tannins to keep them from
decaying and to keep them pliable. Technically, the term “tanning” refers to the process by which collagen fibers in a hide react with a chemical agent (tannin, alum or other chemicals), but the term leather tanning also commonly refers to the entire leather making process.5
The most common tanning agents used in the U. S. are trivalent chromium and vegetable tannins extracted from specific tree barks.6 )
The best tanning factories/companies are from German, US, Italy. Many of them have branches in Asia, Europe, USA or South America. Most of Asia countries do not have the technology/skills/machine to do the tanning process; Asia countries also do not have the big cow to produce large lather/briefcases. Big cows normally come from Brazil, Texas or Europe. After the cow was slaughter in the local like Texas, the cowhide with fur/blood will be sent to South Asia, like Vietnam, to remove the fur and blood due to heavy pollution reason; then the clean half product will be sent to other countries to do the final process, like tanning. One of leather factory in Shangdong China every day export 40,000 square feet to US state for auto leather seats purpose. Mexico also produces some leather; the leather from Mexico normally is thick and stiff. One of well known leather companies based on Texas who sell leather bags online has tanned factory on Mexico board and produce quite heavy leather bags as well.
1.http://en.wikipedia.org/wiki/Tanning 2.http://www.squidoo.com/cows-to-jackets 3.http://www.leatherresource.com/history.html
4.http://www.publicbookshelf.com/public_html/The_Household Cyclopedia_of_General_Information/historyof_cff.html 5.http://serc.carleton.edu/woburn/issues/tanning.html) 6.http://www.epa.gov/ttnchie1/ap42/ch09/final/c9s15.pdf#search=%22leather%20tanning%22