Leather is the oldest continuously used material known to man.  Its use pre-dates recorded history and although the processes used to preserve it have changed over time, it has never been improved upon as a clothing material.  It is durable, breathable and abrasion resistant.  Many cultures believed that when they wore the skin of another animal they took on some of that animal’s characteristics and gained some of its strength.  Wearing leather communicates that strength as well as purpose and identity.

What is Leather?

Leather is created when the hides and skins of animals are tanned.  Tanning is a process that converts the skin into a durable, long-lasting and versatile natural material that is almost impossible to rip.

Types of Skins Used to Make Leather

The most common type if skin to use for leather is cattle skin, but leather can be made from a wide variety of other animal skins including lamb, hog, goat, sheep, deer, kangaroo, ostrich, alligator, shark, and stingray.  Leather made from different animal skins have different qualities which make them desirable for different types of products.

~     Lambskin is prized for its softness and is popular in more expensive apparels and accessories.

~     Deer Skin is possibly the toughest leather in the world and is prized for use in coats and high quality leather accessories like handbags and wallets. It commands a high price owing to its relative rarity as well as its proven durability.

~     Stingray Skin Leather, also known as Shagreen, is tough and durable as hard plastic.  It is used in wallets and belts in the same way as regular bovine leather, and is often dyed black and covered with tiny round bumps in the natural pattern of the back ridge of an animal.  These bumps are then usually dyed white to highlight the decoration.

~     Kangaroo Skin is used to make items which need to be strong but flexible.  It is the only material used in high quality bullwhips.  Kangaroo leather is favored by some motorcyclists for use in motorcycle leathers specifically because of its lighter weight and higher abrasion resistance compared to cowhide, thus providing greater protecting in case of a fall on the roadway. Kangaroo leather is also used for high performance soccer footwear.

~     Ostrich Leather is considered one of the finest and most durable in the world and is currently used by many major fashion houses such as Hermès, Prada, Gucci, and Louis Vuitton.  Ostrich leather has a characteristic "goose bump" look because of the large follicles from which the feathers grew.

~     Bison Leather is popular in the United States, and is rugged and supple with a waxy feel.  It is often used for gloves, jackets and some baseball gloves.

How Leather is Made

Leather is created from animal skins by undergoing a complex, multi-step process.  All true leathers undergo three general processes—preparatory stages, tanning, and crusting—and an additional process, called surface coating, is also sometimes included for specific desired results.

~    Preparatory Stages are when the skin is prepared for tanning.  This stage can include several different processes such as splitting, liming, bleaching, soaking, and many more processes.  Not all processes are used for all leathers.

~     Tanning is when the skin fibers are stabilized for resistance to bacterial attack and decomposition.  After tanning the hides will remain flexible when dried and show an increase in thermal stability.  Tanning includes processed called penetration and fixation.

~     Crusting is when the skin is thinned, retanned and lubricated.  If the leather is going to be colored, a dying process is included in this stage.  The culmination of the crusting process is the drying and softening operations.  Crusting may include several different operations including splitting, shaving, rechroming, neutralization, stripping, whitening, fixation, setting, conditioning, and buffing.

~     For some leathers a Surface Coating is applied and the leather is considered “finished.”  Finishing operations may include: oiling, brushing, buffing, spraying, polishing, plating, embossing, and glazing.

Types of Tanning Processes

There are several tanning processes that are used to transform the skin of an animal into supple, strong leather.  Each process has its own definitive results.

~     Vegetable-Tanned Leather is leather tanned with tannins found in vegetable matter, such as the extracts of trees, barks, fruits, and leaves.  It is supple and brown in color, with the exact shade depending on the mix of chemicals and the color of the skin. Vegetable-tanned leather is not stable in water; it tends to discolor, and if left to soak and then dry it will shrink and become less supple and harder.  In hot water, it will shrink drastically and become rigid and eventually brittle.  Boiled leather is an example of this where the leather has been hardened by being immersed in a hot substance such as hot water or hot wax.  The natural oils remaining in vegetable tanned leather can be washed out with repeated exposure to water.  To improve water resistance, these leathers can be oiled to supplement the natural oils remaining in the leather.  Frequent oiling with mink oil, neatsfoot oil or a similar product, keeps it supple and improves its lifespan dramatically.

~     Chrome-Tanned Leather is leather tanned using salts of chromium.  It creates leather that is more supple and pliable than vegetable-tanned leather, and does not discolor or lose shape as drastically in water as vegetable-tanned leather.  It is also possible to achieve more esoteric colors when using chrome tanning.

~     Aldehyde-Tanned Leather is tanned using compounds of glutaraldehyde or oxazolidine.  This is the leather that is often refered to as wet-white leather due to its pale cream or white color.  Aldehyde leather is the most common chrome-free leather, and is often used to make infant's shoes and automobile upholstery for automobile makers that prefer to use chrome-free leather.  Formaldehyde tannin is a method of aldehyde tanning that is rarely now used due to the danger to workers of formaldehyde exposure.  Brain-tanned leather, and Chamois leather fall into the category of aldehyde-tanned leather, and are known for their exceptional softness, water absorbent capabilities, and their ability to be washed.  Brain tanned leathers are made by a labor-intensive process which uses emulsified oils often derived from animal brains.  Chamois leather is made by using oils that oxidize easily, such cod oil, to produce the aldehydes that tan the leather.

~     Synthetic-tanned leather is leather that is tanned using aromatic polymers.  Leathers tanned with this method are white in color.

~     Alum-tanned leather is tanned using aluminium salts mixed with a variety of binders and protein sources, such as flour, egg yolk, etc.  Leather made in this way is technically not leather (it is often considered “tawed,” not tanned) because the resulting material will rot in water.  It is not as supple as vegetable-tanned leather, but very light shades of leather are possible using this process.

Thickness of Leather

The thickness of a hide is referred to as its millimeter.  There is no one millimeter that is better than another as each millimeter can be used to satisfy different needs.  The lightest weight leather is thin millimeter “shirting” suede which has extraordinary drape, suppleness, and flexibility.

Causes of Leather Deterioration

Although it takes a long time, the natural fibers of leather will eventually break down with the passage of time (it takes 25-30 years for a pair of leather shoes to decompose).  Leather deteriorates primarily in the following ways:

~     Oxidation caused by excessive dryness.  Surface cracking and flaking, and over-all weakness are signs of oxidation, and are most often seen in very old, dry leather.  Oxidation will eventually turn leather to dust.  Thoroughly treating leather with leather care lotion reduces the effects of oxidation.  Oxidation is accelerated when leather is exposed to high heat.

~     Chemical damage caused from exposure to ultraviolet light, ozone, pollutants, or from chemical reactions following treatment with tallow or oil compounds.  Like oxidation, chemical damage is accelerated when leather is exposed to high heat.  Leather should be stored away from heat, and not needlessly exposed to sunlight.

 ~     Internal chafing or breaking of fibers when very dry leather is flexed.  Keeping your leather item lubricated will allow the fibers to slide one against another.  Dry leather should not be flexed until it has been thoroughly lubricated.

~     Abrasion from external sources, or internally from dirt particles ground into the leather.

~     Red rot.  Vegetable-tanned (acidic) leathers are vulnerable to a condition called red rot, which causes powdering of the surface and a change in consistency of the leather.  Damage from conditions such as red rod is aggravated by high temperatures and high humidity, and is irreversible.