What is the Leather?
Leather is a natural durable and flexible material created by tanning animal rawhides and skins. The most common raw material is cattle hide. It can be produced at manufacturing scales ranging from artisan to modern industrial scale.
Leather is used to make a variety of articles, including footwear, automobile seats, clothing, bags, book bindings, fashion accessories, and furniture. It is produced in a wide variety of types and styles and decorated by a wide range of techniques. The earliest record of leather artifacts dates back to 2200 BC.
The leather manufacturing process
The leather manufacturing process is divided into three fundamental subprocesses: preparatory stages, tanning, and crusting. A further subprocess, finishing, can be added into the leather process sequence, but not all leathers receive finishing.
The preparatory stages are when the hide is prepared for tanning. Preparatory stages may include: soaking, unhairing, liming, deliming, bating, bleaching, and pickling.
What is Tanning Process?
Tanning is a process that stabilizes the proteins, particularly collagen, of the raw hide to increase the thermal, chemical and microbiological stability of the hides and skins, making it suitable for a wide variety of end applications. The principal difference between raw and tanned hides is that raw hides dry out to form a hard, inflexible material that, when rewetted, will putrefy, while tanned material dries to a flexible form that does not become putrid when rewetted.
Many tanning methods and materials exist. The typical process sees tanners load the hides into a drum and immerse them in a tank that contains the tanning “liquor”. The hides soak while the drum slowly rotates about its axis, and the tanning liquor slowly penetrates through the full thickness of the hide. Once the process achieves even penetration, workers slowly raise the liquor’s pH in a process called basification, which fixes the tanning material to the leather. The more tanning material fixed, the higher the leather’s hydrothermal stability and shrinkage temperature resistance.
What is the Crusting process?
Crusting is a process that thins and lubricates leather. It often includes a coloring operation. Chemicals added during crusting must be fixed in place. Crusting culminates with a drying and softening operation, and may include splitting, shaving, dyeing, whitening or other methods.
For some leathers, tanners apply a surface coating, called “finishing”. Finishing operations can include oiling, brushing, buffing, coating, polishing, embossing, glazing, or tumbling, among others.
Leather can be oiled to improve its water resistance. This currying process after tanning supplements the natural oils remaining in the leather itself, which can be washed out through repeated exposure to water. Frequent oiling of leather, with mink oil, neatsfoot oil, or a similar material keeps it supple and improves its lifespan dramatically.
What Type of Leather Is Available?
Leather comes in various forms depending on the production processes. These forms include:
Brain Tanned Leather:
It is particularly soft and washable. The production of this form of leather uses emulsified oil that are mostly extracts from the brains of animals.
Vegetable Tanned Leather:
Supple and delicate, needing a relatively high level of maintenance. It can harden, shrink, or even become brittle if soaked. The production of this type of leather uses extracts from vegetables, fruits, tree barks, roots, among other plant extracts.
Synthetic Tanned Leather:
It is white in color and is made through a process that uses aromatic polymers (synthetic plastics).
It has good water absorption qualities and made via a process that also uses oils that oxidize, producing aldehydes.
Chrome Tanned Leather:
It is slightly liable to drastic changes in its shape and texture when in water. It is made from a production process that uses chromium sulfate and other chromium salts.
This is the end product of an animal hide processed using the simplest of methods that involve scraping the skin to achieve a thin layer, and soaking the hide for some time, stretching it as it dries. It is stiff, brittle, and not commonly considered actual leather.
Other forms of leather include Alum-Tanned Leather, Rose Tanned Leather, Aldehyde-Tanned Leather, and Formaldehyde Leather.