Leather is a durable, historic material manufacturered by tanning hides and skins of many types of animals, usually cows, pigs and sheep. Tanning converts the putrescible skin into a durable, natural material for various uses.

Leather is an extremely important commodity with thousands of uses. Together with wood and stone, leather was rooted in ancient technology and continues to this day. What differentiates the leather industry from the fur industry is in the source of their raw materials. Leather is a byproduct of the beef industry. The fur industry is not a byproduct because while the meat is used, generally speaking it is the meat that is considered a byproduct. Taxidermy makes use of animal skins, typically the head and back are most heavily utilized. Hides and skins are also used to make glues and geletins.

There are a number of processes where an animal skin can be transformmed into leather or leather wallets.

Vegetable-tanned leather is tanned with tannins and other natural reagents found in vegetable matter, tree bark, and other sources. It is brown in color with the specific shade depending on the relative chemical mixture and the underlying color of the hide. Vegetable-tanned leather is unstable in water. Water will discolor it, and if left to soak and dry it shrinks becoming less supple and virtually brittle. Hot water will shrink it drastically making the leather rigid and eventually brittle. Boiled leather is where the leather is purposely hardened by being immersed in hot water, wax or similar hot liquids. Historically, 'boiled leather' was used in armor (also book binders) since it was hard yet light weight. For leather carving or stamping, this is definitely the leather to use.

Chrome-tanned leather, invented in the 19th century, is tanned with chromium sulfate and chromium salts. It is more supple and pliable than vegetable-tanned leather, and reacts much better with water since it will tend not to discolor. A greater range of colors is also possible with chrome based leathers.

Aldehyde-tanned leather is tanned using glutaraldehyde or oxazolidine compounds. Most tanneries refer to this as 'wet-white' leather due to its color. It is the main type of leather used in baby shoes and in cars. Formaldehyde tanning (extremely dangerous) is yet another aldehyde tanning process. 'Brain-tanned' leathers are of this type and are known for water absorption. "Brain tanned" leathers are labor-intensive using oils derived, quite literally, from animal brains. They are soft and can be easily washed with water. "Chamois" leather is also aldehyde tanned the only difference being that Chamois leather is made using cod oil that oxidizes easily to produce the aldehydes required to tan the leather.

"Synthetic-tanned" leather is tanned using Novolac or Neradol polymers. This white leather was invented when vegetable tannins were in short supply during WWII. Melamine and resins are also synthetic and provide filling other leathers require. Urea-formaldehyde resins were also used until people realized that free formaldehyde was being formed (again, very dangerous)

"Alum-tanned" leather is tanned with aluminium mixed with protein sources like flour or egg yolks. Many would argue that this is not truly a leather inasmuch as the item is not technically tanned. Nevertheless, this process produces very bright colors that are very popular and not otherwise possible with vegetable-tanned leather.

Rawhide is manufactured by literally scraping the skin thin (very hard to do even with a machine, this process was featured on the show "Dirty Jobs"). After which it is soaked with lyme and then fully stretched taut until it dries completely. Rawhide is stiff and relatively fragile despite its tough guy name, but its useful for things like drums or for applications where the leather does not need to flex.

Leather can be oiled to repel water. Frequent oiling with some sort of oil based leather conditioner keeps the leather soft and increases lifespan dramatically.

At the upper end of the leather spectrum is "Full-Grain leather," which is a clean and natural leather which has not been corrected since very few imperfections existed in the natural hide. Only the cow's hair is removed (by the way, the hair is utilized to make rope) The leather remains natural which permits greater fiber strength and increased durability. The natural grain also breathes better and is more comfrotable in clothing, particularly leather jackets. Full-Grain Leather wears better and rather than simply wearing out it will slowly charmelize and devlelop a patina which many argue makes the leahter obtain a charachter. Aniline leathers are almost always a full-grain leather.

Top-Grain leather is fuzzy on one side and smooth on the other. The smooth side is the outter side. The hides are made from slightly inferior quality raw materials and the natural grain has been removed and the smooth surface applied. Top-Grain leathers are usually painted, but despite this they are typically still relatively important because it must be remembered that the imperfections in the hide are caused by the cow living its natural life, things like insects, barbed wire and other rigors of life do mark the animal making full-grain leathers relatively rare.

With suede, the grain is completely removed and it is often an interior split of the hide (ie. the inside of the skin is now what you see facing out).During the splitting operation the grain and drop split are separated with a precise machine. The drop split can be split yet again to get a middle split. With thick hides, if you can believe it, it can theoretically be split yet again.

The best suede is made from the flesh split shaved to the correct thickness and it is often fuzzy on both sides. Its less durable than top grain leather but it is cheaper because from the same piece of hide, more suede can be produced.. Suede is "fuzzy" on both sides. Suede is less durable than top-grain. Suede is cheaper because many pieces of suede can be split from a single thickness of hide, whereas only one piece of top-grain leather can be made. However, tanneries apply different techniques to make it appear more like full-grain leather, particularly by mixing glue with one side and passing the suede through rollers. This type of suede is referred to as Latigo and is often used in cheaper leather products.

Patent leather is a high gloss finish seen in wedding shoes and evening bags for special events. It typically has some sort of plastic coating and was invented by S. Boyden in Newark, NJ in the 19th century.

Vachetta leather is used as trimmings in luggage. It is often untreated and can be stained by water and sunlight will also tend to discolors it.

Slink is a very rare leather and it is made from the skin of an unborn calf and it is prized to make the softest gloves. It is extremely expensive since its only source are cows that quite literally die pregnant.

Slink is leather made from the skin of unborn calves. It is particularly soft, and is valued for use in making gloves.

Nubuck is top-grain cattle leather which has been sanded, but has not been completely smoothed, which gives the leather a velvet like feel.

Belting leather is a full grain leather that was originally used in industry. It is often found on the surface of briefcases and wallets, and can be identified by its thick, firm feel and smooth finish. Belting leather is often favored for these applications because it is one of the few leathers that can retain its shape without an independent frame.

Napa leather is soft and supple, typically found in personal items because it is of relatively low cost, and is often derived from sheep.

Leather made from exotic skins have been in heavy demand and many reptiles have been hunted down just to obtain skins. Alligator is an excellent example of this phenomenon. Alligator populations have survived, but demand has not really dropped, pushing prices for alligator skins to all time highs.

Leather Preservation: The natural fibers of leather will biodegrade with the passage of time. Acitic leathers are subject to red rot which powders the surfaces and changes the leather's consistency. High temperatures and humidity will aggravate the problem.

Exposure to long periods of low relative humidities can cause leather to become desiccated, but nevertheless the greatest threat to leather still remains water and high humidities.

Many cars come with leather seating which can be a cheap vinyl or a nappa leather found in upscale cars.

Leather takes a long time to biodegrade, but it DOES biograde, which is why, for instance, it is rare to find examples of ancient leather from the Romans or the Egyptians unless the leather was preserved in some sort of bog pit.

Concern for animals:

Some vegans and animal rights activists boycott leather advocating the use of synthetic leathers like PVC. Notwithstanding, the basic argument that leather is unethical is fundamentally related to whether beef consumption is ethical. If you opine that beef consumption is ethical, and that it is okay to raise beef cows, then there is an ethical obligation to utilize the animal which has been slaughtered for the greatest possible good, and that does include the leather the animal provides us.