Tannin in the leather tanning industry
Your closet most likely contains vegetable tanned leather purses, shoes and jackets, chosen for their elegance, resistance and durability. Perhaps you have a leather sofa, in your living room or a leather interior in your car. Or maybe you chose a leather case for your cell phone or tablet.
Wait a moment and think: leather is an organic material made from protein fibers. And like all other organic materials, it should rot and decompose with time. Instead, an article made of good-quality leather can last for generations.
Have you ever asked yourself how this is possible?
It’s simple: the secret lies in the tanning process, which is capable of impeding the decomposition of the hides, making them unalterable or rot-proof, resistant and ready to be further processed.
There are, in fact, various types of tanning processes: the most well-known and commonly used ones are vegetable tanning, which exclusively uses tannins as tanning agents, and chrome tanning, which uses tannins in only some phases of the process.
The Raw Material: Animal Hides and Skins
The animal hide or skin is a by-product of the meat industry. If it was not used in tanneries, it would rot and become another waste product to be disposed of.
The tanning process prevents leather from decomposing. The leather takes on the properties of resistance, elasticity and softness, preparing it for further processing. In this way, the leather becomes an extremely supple material that can be used for different applications from bags to shoes, from belts to jewelry, but even for leather sofas and armchairs, cell phone and tablet cases, clothing and outerwear.
Thanks to some special processing techniques, it is possible to obtain leathers with different characteristics, tailored to specific articles: this will produce leather of varying degrees of softness or pliability or particular shades of color.
The most widely used hides and skins in the tanning industry come from cows, sheep and sometimes pigs, all animals that are all raised for nutritional purposes. No animal is killed for the sole purpose of leather production.
Tannin, a Precious Natural Ally
Tannin is able to bind to proteins and stabilize their structure: once the tanning process is completed, it remains permanently fixed within the fibers of the leather.
This is an important feature to explain the absorbent and breathable properties that tannin confers to the leather. Think about the shoes we wear every day: physical activity, the heat, or even the simple contact with the foot are all factors that increase the temperature and humidity inside the shoe.
We all know the consequences: heat, swollen feet and the generation of unpleasant smell make us embarrassed when we take off our shoes. The origin of stinky shoes is related to the activity of bacteria, which proliferate in hot and humid environments.
Shoes with vegetable tanned leather interiors allow to maintain a dry and comfortable environment. Recent researches have shown that tannin can balance the bacterial population of the shoe, thus acting directly on the cause of the bad smell in a natural and safe way.
Vegetable tanned leather with tannins inhibits the formation of unpleasant odors. Tannin prevents the shoe environment from becoming favorable to bacterial proliferation by fostering the absorption of sweat. This environment is therefore no longer a bacteria incubator. Every time we wear shoes with vegetable leather interiors the foot remains fresh and dry.
The 4 Phases of the Tanning Process
The tanning of hides and skins is a complex and diversified process: in fact, it can be adapted depending on the type of final product desired.
Nevertheless, the process can be divided into 4 macro-phases:
Preparation
When the raw hides arrive in the tannery, they are thoroughly washed, to remove the thick layer of salt used to preserve them during transport. Then they are dehaired, and finally fleshed, to scrape off the all the organic residue. The hides then undergo a preliminary treatment which also involves cutting or splitting.
Tanning
This is the heart of the entire process: generally, the hides are loaded into drums and immersed in a solution of tanning agents. The drums continuously rotate to allow the tanning product to penetrate into the fibers of the hide or skin. The alternative, which requires more time, is to immerse the hides into large vats with gradually increasing concentrations of tanning agents (as is the case for vegetable tanning).
Retanning
The tanned hide can undergo a retanning treatment, or a second tanning phase, in which different tanning agents are generally used. Tannin is normally used for retanning chrome tanned hides. This is an important detail because chrome tanned leather and retanned with tannins will then acquire the beneficial properties of vegetable tanned leather. The hides are then fatliquored, or greased, to achieve the desired degree of softness for the finished article, and then dried.
Finishing
The leather is coated with pigments or oils to impart its characteristic appearance and consistency. The leather is now ready to be worked and transformed into purses, belts, shoes and many other articles.
Tannin in the Tanning and Retanning Processes
Vegetable tanning is the oldest known form of tanning in the world being its processes used today are essentially as they were during the Middle Ages and the Renaissance. These ancient methods, combined with the modern technology, produce extraordinary results.
Tannins are versatile products that can also be used in vegetable retanning, for example on chrome tanned leathers. This process makes the product suitable for a wide range of end applications, from traditional leather articles, to water-repellent shoes and automotive interiors.
Learn more about Vegetable Tanning
The vegetable tanning process is the result of a long artisanal tradition that has been passed down for centuries and is still the method adopted by the most renowned fashion houses. This process is a precious cultural heritage that still plays a vital role in today’s leather industry. Would you like to find out how vegetable tanned leather is made? Go to the dedicated page and learn about the entire process, step by step.