It's no surprise that the production of leather dates back nearly as long as human history. Ever since man has hunted animals for food, we've used their skins for shelter, clothing and equipment. As a byproduct of the food industry, leather manufacturing and the production of leather goods continues to evolve today, turning what would otherwise be waste—the hide of an animal—into beautiful clothing, furniture, accessories and more. But how did it all begin?
The earliest uses of animal skins presented a significant challenge—if left untreated, the skins were susceptible to drying out or rotting, rendering them useless.
History of Tanning
Methods of preservation had to be developed to maintain the flexibility of the skin and prevent decay. Initial attempts included drying them out in open air and sunlight, rubbing animal fats into the skin, smoking them over an open fire, and eventually soaking them in a bath of twigs, bark and leaves. This last technique, using plant products to soften and preserve the hide, lead to the development of what we now know as the vegetable tanning process.
From the Old Germanic word "tanne" meaning fir or oak tree, "tanning"—a complex technique of turning an animal's skin into leather—refers to the use of tree bark rubbed into the skin as a part of the preservation process. While civilizations throughout Europe, Asia and North America developed their own methods, it's the Ancient Greeks who can be credited with creating the first vegetable tanning recipes.
As societies advanced, so did the development of the tanning process. At once a closely guarded secret handed down from father to son, trade guilds evolved to protect and promote the art of tanning, which eventually lead to royal charters being issued, authorizing the official production of leather.
Later, in the 18th century, new tanning techniques had to be developed to respond to new applications of leather particularly for upholstery and fine clothing, which required a softer leather than that produced by vegetable tanning. The addition of chromium salts to the process lead to the development the chrome tanning process, which could easily produce softer, supple leathers in a fraction of the time it takes to produce vegetable tanned leather. Today, we still use two primary methods of leather manufacturing—vegetable tanning and chrome tanning—produced in factories known as "tanneries".
A note on the difference between the use of the words hide and skin. "Hide" refers to the skin of large animals, such as cattle, horse and bison. "Skin" is used to refer to smaller animals, such as calf, lamb or goat.
The Tanning Process
Today's production of leather involves three primary processes to produce leather with a final or finishing process to prepare the leather for garment or product production:
Once the animal is killed, the skin is removed while the body heat is still in the tissue of the skin, and then fleshed to remove any meat or fat tissue from the skin. The next step is to salt cure the hide if it's not immediately being tanned. Curing the hide pulls water away from the skin so as to prevent rotting and bacterial growth for storage until the hide is to be tanned.
When the hide is ready for tanning, it goes through several preparatory steps known as the Beamhouse operations:
- Soaking—The first step is to soak the hide in drums of clean water where paddles and mixers massage the hide to remove the salt from the curing process and reintroduce moisture.
- Liming—The next step is to treat the skin with a milk of lime, preparing the hide by removing additional hair, modifying the protein structure, swelling the fibers, and removing fats and grease within the hide.
- Unhairing and Scudding—An unhairing agent is applied to the skin as the hide is turned in a machine to remove excess hair. Finally, a tanner uses a knife to remove any final hairs in a process called "scudding".
- Deliming and Bating—Next, the hide is placed in a drum where a deliming agent is worked into the hide using a paddle to bring down the pH balance and remove the alkali from the hide introduced during liming. At this point, enzymes soften the hide in preparation for the tanning process.
- Pickling—The final step in the Beamhouse operations is pickling, which treats the hide with salt and sulfuric acid to help facilitate the penetration of the mineral agent.
As we mentioned above, there are two primary methods of tanning: vegetable and chrome tanning. Vegetable tanning involves the extraction of tannins—a naturally occuring chemical in barks and plants—which the skin is soaked in to ultimately render the hide into a leather that is flexible and resistant to bacterial growth.
Uses: shoe soles, saddles, belts, luggage
Chrome tanning involves the use of chromium salts and man-made ingredients rather that plant or bark based chemicals. The advantages of chromium tanning is that it's faster and renders a leather that is much more pliable than the slightly stiffer vegetable tanned leathers.
Uses: upholstery, bags, fine leather accessories, garments
After the tanning process is complete, the leather goes through various stages to make it ready for product production.
- Splitting—The hide is placed through a machine with large blades to thin the leather to it's proper thickness.
- Dyeing—Oil dyes and finishes are added to the hide along with various fats, waxes, resins and water.
- Staking—A process that soften certain leathers for garment or bag production.
- Milling—Dry vessels which brings the leather to its desired softness.
- Finishing—The final steps necessary to even the color, cover imperfections, make a cleanable surface, and add any cosmetic finishes.
*Images courtesy of Horween Leather Company.