Leather, a flexible and durable material created from animal rawhide and through a tanning process, comes in a variety forms. Leather undergoes a long, arduous process to produce luxurious and tough material that can be found in books, automobiles, shoes, jackets, drum heads, and dog chews. Leather has an extensive history, sometimes used for armory after hardening, and becomes increasingly popular to preserve documents and other important texts. In fact, leather can be oiled to improve its water resistance to supplement those already existing oils within the animal skins themselves. These oil supplements include mink oil, neatsfoot oil or other similar materials.

Various Leather Production Processes:

The manufacturing process of leather entails three different sub-processes, including prepping, tanning, and crusting stages. In fact, all authentic leather will undergo these exact sub-processes. A fourth sub-process known as surface coating might also be added to cover imperfections. These operations vary with each form and type of leather.

• Langston University: Tanning Goat Hides (PDF) ��� An extensive guide authored by Dr. Roger C. Merkel that describes the tanning process of goat hides.
• Leather Tanning by Spencer Black (PPT) ��� A power-point slide presentation covering the leather tanning process.
• Pergamena.net: How Leather is Made ��� A step-by-step description covering the leather manufacturing process of vegetable tannage.
• Carleton College: History of Leather Tanning in Woburn ��� A brief historical background on leather tanning in Woburn, Massachusetts.
• Duke University: Leather Footwear Industry ��� Labor Factors: An extensive overview of the labor factors concerning the leather footwear industry.
• South Dakota State University: SDSU Research Could Improve Leather Tanning ��� A short article addressing how research conducted at South Dakota State University could help advance the leather tanning process.
• Elaw.org: The Scope for Decreasing Pollution Load in Leather Processing (PDF) ��� An extensive report about hair-saving methods to decrease pollution in the leather production industry.
• Indian Leather Technologists' Association: Greener Leather Processing: New Avenues (PDF) ��� An extensive report introducing greener leather processing methods for a cleaner environment.

Leather Forms and Types:

There are various leather forms and types manufactured for many different products. Some forms include all natural ingredients spawned from vegetation which are used during the tanning process, while others are beginning to receive health recognition for both workers and consumers. Leather can be fashioned in many colors, textures, and levels of durability. In fact, some methods have existed throughout history to bring about the same reliable material made to endure the roughest conditions.

• Conservation Online: Vegetable-tanned Leather ��� Vegetable-tanned leather consists of a process using tannin and other additives found in vegetation. This leather has a supple-brownish color with little to no variance in the shades produced from the different mix of chemicals and color. Vegetable-tanned leather has a usability specific to leather carving and stamping. It has a special place in history for book binding, and occasionally fitted for armory after solidifying.
• United Nations Industrial Development Organization: Chrome Balance Leather Processing (PDF) ��� Chrome-tanned leather, formed from chromium sulfate and other salts derived from chromium, has a composition more supple and pliable than leather tannage originating from vegetable matter. It has a wet-blue color with varying colors down the spectrum.
• Leather Research Laboratory: Formaldehyde-tanned Leather ��� Formaldehyde tanning, a dangerous substance for workers and customers alike, uses a variation of aldehyde tanning, such as brain-tanning, or using emulsified oils made from animal brains. Chamois leather, another form of aldehyde tanning, uses cod oil to oxidize and easily produce the existing aldehydes that tan the existing leather.

• Synthetic-tanned leather uses scented polymers, such as Novalac and Neradol, which produces an off-white color and was first invented due to a shortage of vegetable tannins during World War II. Melamine and other amino acids provide the filling of modern-day leathers.
• Types of Leather ��� Rawhide leather, made by scraping animal skins thin, soaking it in lime for a restricted amount of time, and then stretching it over a flat-bed to allow it to sundry, has a stiffer and more brittle composition than other leather forms. Rawhide is usually found on drum heads and dog chews.
• Full-grain Leather consists of pre-cut top grain and split layers. It has not been treated through sanding, buffing or snuffing methods in order to remove existing imperfection and natural marks on the surface of the rawhide. High-quality full-grain leather can usually be found in two finish types including aniline and semi-aniline. These two types create a vast assortment of furniture and footwear on the consumerist market.
• What is Top Grain Leather? ��� Top-grain leather, the second-highest quality consists of a separate, split layer, which makes it thinner and more pliable than full grain leather. Top-grain leather has a sanded surface and finished coat added to the leather's surface to make a colder, plastic feel. This type of leather does not cost as much in comparison to other types.
• Leather Terms Glossary: Corrected-grain Leather ��� Any leather with an artificial grain applied to its surface qualifies as corrected-grain. These hides do not meet the standards for vegetable-tanned or aniline leather. Any existing imperfections are corrected, sanded, and impressed into the surface before being dressed with the desired stains and dyes.
• Split Leather ��� Split leather, fabricated from the fibrous portion of the hide once the rawhide has been removed from the hide itself. The top-grain and drop-split are separated during the splitting operation. Suede manufacturers typically use split leather to create the clothing, furniture, and other materials.

Environmental Impact of Leather Tanning:

Leather tanning imposes a high environmental impact on livestock and through chemical pollution of land, air, and water during its manufacturing process. Some of the chemicals emitted into our atmosphere and environment include hydrogen sulfide and ammonia. Leather also requires 25 to 40 years to fully decompose after taxing its utilitarian value. In fact, one ton of hide produces toxic levels of chromium in living bodies of water surrounding leather tanning facilities. Pesticides and solid byproducts left over from the tanning process considerably strains water treatment installations all over the world.

• Environmental Hazards of Leather ��� A brief article covering the environmental hazards of leather tanning.
• Leather Processing: Cleaner Production Fact Sheet and Resource Guide (PDF) ��� An extensive chapter addressing the conversion over to cleaner, leather tanning production processes.
• Toxicity Reduction in Leather Tanning Wastewater by Improved Coagulation Flocculation Process (PDF) ��� A detailed report presenting toxicity statistics and methods to improving wastewater runoff levels from leather tanning facilities.
• The History of Pollution ��� A short overview addressing the history of pollution and the total impact the industrial fields consisting of oil, coal and leather tanning have made on the environment.
• United Nations University: Colors of Water: Bangladesh's Leather Tanneries ��� A short article addressing the toxic wastewater produced by the leather tanneries in Bangladesh.
• Columbia University: Chromium-6 Found in Tap Water of 31 U.S. Cities ��� A short article addressing a water survey that detected chromium-6 in the water supply of 31 U.S. cities.
• A Case Study of the Leather Industry in Brazil (PDF) ��� An extensive case study covering the leather industry in Brazil, including the pollution produced from the native leather tanning facilities.
• Leather Tanning and Finishing Facilities Fact Sheet (PDF) ��� An extensive fact sheet providing statistical data of the leather tanning and finishing facilities in Florida.
• Measures Taken Against Water Pollution in Tanneries and Leather Finishing Plants (PDF) ��� A publication that addresses adjusted measures to eradicate water pollution produced by leather tanneries and finishing plants.
• Leather and Tanning ��� A short article addressing the leather tanning process, including the pollution it produces from Chicago plants.