The Vegetable Tanning Process
Of all leather processing methods, vegetable tanning is the oldest.
It is believed to date back to Prehistory, when humans learned to transform the hides of animals killed during hunting in garments and utensils (you find many other curiosities on the page History of Tannin).
Vegetable tanning has evolved over the centuries, through the selection of the most suitable plants to extract the tannin and the efficiency improvements of the production methods.
However, the fundamental phases have remained unchanged until today, passed down between generations as a precious artisan tradition. In particular, vegetable tanning is used to produce hard leather that, thanks to its resistance, can be used for leather soles and in some furnishing components.
This workmanship is due to the ability of the master tanners make the vegetable tanned leather a unique product, which ages but does not decay. In addition, the tannin present in vegetable tanned leather can play an important role in the fight against bacteria.
Photo: Courtesy of the Vera Pelle – Genuine Italian Vegetable Tanned Leather Consortium
Vegetable Tanning: a Great Artisan Tradition
Vegetable tanning is a real art that passed down from generation to generation.
The best tanners jealously guard their secrets. Each one conceals an old special recipe combined with state-of-the-art technology.
The type of tannin used, the doses, the tanning times and the processing methods make the difference.
All with the care and dedication that requires a natural process, with slow production times.
Of all the tannin applications, this is certainly the one with the oldest tradition.
The process has remained practically unchanged over the centuries, except for few concessions to modernity introduced in recent times.
A Method that Gives Unique Results
Bags, belts, shoes, mobile covers and all other objects made of vegetable tanned leather are three times unique: because they are the result of an artisan process; because they are created with unique materials and because in time they absorb the traces of our experience over time.
Being natural products, the animal hides have actually small differences: a sign, a different shade that characterizes them.
Tannin plays a fundamental role within the tanning process. Besides stabilizing it, tannin imparts to the leather unique properties, able to withstand all subsequent processing stages.
In addition, items made of vegetable tanned leather are completely natural products, therefore safe even for people with particularly delicate skin or sensitive to allergies.
The Tuscan Leather District
Some territories in Italy have a tradition of vegetable tanning that lasted over the centuries. Among these, the Tuscan leather district of Santa Croce sull’Arno, between the provinces of Pisa and Florence, is the area with the concentration of 35% of the national production of leather and 98% of the production of vegetable tanned leather and leather soles. To learn more, visit the page History of Tannin.
%
of national leather production
%
of national production of vegetable tanned leather and leather soles
Vegetable Tanning: Features and Benefits
Warm colours, with reddish-brown shades, and an intense scent of wood.
It promotes a sustainable economy, respecting local communities and natural resources.
It is the heir of an ancient and noble artisan tradition, carried out for centuries.
If necessary, it can be integrated with other tanning methods.
It is by far the tanning method with the least environmental impact.
The products evolve over time, absorbing the traces of our lives. They become unique.
According to scientific researches, tannin is a precious resource in the fight against bacteria.
At the end of its life, the leather treated with tannin is compostable organic waste.
The Stages of Vegetable Tanning
The process consists of 3 stages: a preparatory phase, called beamhouse; the proper tanning phase and a final stage (post-tanning) in which the freshly tanned leathers are prepared to meet the needs of leather craftsmen, in order to turn them into shoes, bags, belts and many other commonly used items.
1- Beamhouse (preparation of hides)
1- Soaking
The hides obtained as the scrap of slaughterhouses undergo a salting processing, which blocks the decomposition and facilitates the transport. As soon as they arrive at the tannery, they must be washed, cleaned and rehydrated.
2- Liming
Deletion of all unnecessary parts (hair, epidermis, nerves, subcutaneous adipose tissue, etc.) and swelling of the hides to allow a better absorption of the tanning products. Traditionally you get this result with a lime bath.
3- Fleshing
Residues of meat and adipose tissue still attached to the hide are removed manually or mechanically, so as to leave the hide perfectly clean.
4- Splitting
La pelle animale, in particolare la pelle bovina, è particolarmente spessa. Per ridurre ed equalizzare opportunamente lo spessore della pelle, lavorarla meglio (e ottimizzarne l’utilizzo) viene spaccata a metà. In questo modo, da una pelle animale se ne creano due più sottili e malleabili. La parte che originariamente guardava all’esterno (e recava i peli) è considerata più pregiata e prende il nome di “primo fiore”.
5- Decalcination and Maceration
The hide, still impregnated with lime, is washed with water and decalcinating agents. It is then treated in a bath with special enzymes to eliminate any residual lime.
1- Beamhouse (preparation of hides)
1-Soaking
The hides obtained as the scrap of slaughterhouses undergo a salting process, which blocks the decomposition and facilitates the transport. As soon as they arrive at the tannery, they must be washed, cleaned and rehydrated.
2-Liming
3-Fleshing
Residues of meat and adipose tissue still attached to the hide are removed manually or mechanically, so as to leave the hide perfectly clean.
4-Splitting
Hides, and above all cowhides, are particularly thick. To reduce and equalize appropriately the thickness of the skin (and optimize its use), it is split in half. In this way, from one single hide we obtain two, thinner and more malleable. The part that was originally external (completely bare hair) is considered more valuable and takes the name of full grain leather.
5-Decalcination and maceration
The hide, still impregnated with lime, is washed with water and decalcinating agents; It is then treated in a bath with special enzymes to eliminate any residual lime.
2- Vegetable Tanning
It is the climax of the whole process. The hides are immersed in a solution of water and vegetable tannins.
The master tanner creates the ideal blend keeping in mind the result he wants to achieve in terms of softness, strength, colour and touch feeling.
He carefully chooses the vegetable sources, the tannin concentrations, the temperature and the tanning times.
A real art of nature.
Vegetable tanning can follow two methods: using tanks or using drums.
The photos of the tanning processes are a courtesy of Pelle al Vegetale – The Italian Vegetable Tanned Leather Consortium
How Does Tannin Link with Hides?
Read more
The skin (“dermis”) is largely constituted by a protein called “collagen”. These proteins are in turn formed by long chains of amino acids that bind together by means of peptide bonds. Each chain is linked to the other by chemical bonds based on hydrogen, called “hydrogen bridge bonds”. The tannin molecule manages to fit into these spaces and to form new hydrogen bonds, through which it “binds” to the fibers of the hide.
3- Post-Tanning Treatments
The tanned hides are dried and subjected to special treatments to make them easier to work and prepare them for different end-use destinations.
1- First Setting Out
This phase consists of pressing the hides to drain the excess water out.
2- Re-tanning
It requires a second drum bath containing tanning agents which can be different or the same as the ones used previously.
3- Fatliquoring
A new step in which special dyes are added in the drum to obtain the desired chromatic effect. The hides are also treated with special oils of plant, animal or mineral origin, to confer to the leather softness and smoothness.
4- Second Setting Out and Drying
A second pressing eliminates any residual water and moisture. The hides are then ready to be dried, according to different methods: simple exposure to air; passage in a drying tunnel with controlled temperature and humidity, microwave, etc.
Un nuovo passaggio in bottale con speciali tinture permette di ottenere l’effetto cromatico desiderato; le pelli vengono anche ingrassate con speciali olii di origine vegetale, animale o minerale, che conferiscono morbidezza e lucentezza.
3- Post-tanning treatments
Tanned vegetable skins are dried and subjected to special treatments to make them workable and prepare them for the respective use destinations. The main features are:
1-First Setting Out
This phase consists of pressing the hides to drain the excess water out.
2-Re-tanning
It requires a second drum bath containing tanning agents which can be different or the same as the ones used previously.
3-Dyeing and fattening
A new step in which special dyes are added in the drum to obtain the desired chromatic effect. The hides are also treated with special oils of plant, animal or mineral origin, to confer to the leather softness and smoothness.
4-Second Setting Out and Drying
From Tanning to Final Consumer
Vegetable tanned leather is ready to be shipped and reach the companies that produce footwear, furniture and accessories but also fashion houses and automotive manufacturers. In these plants they will be transformed and prepared for the most important meeting: the one with you.