Vegetable tanning 

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

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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.

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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

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2-Liming

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3-Fleshing

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4-Splitting

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5-Decalcination and maceration

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Rinverdimento

le pelli ottenute come scarto dei mattatoi vengono sottoposte a un processo di salatura, che blocca la decomposizione e ne agevola il trasporto. Appena giunte in conceria vanno quindi lavate, liberate dalle impurità e reidratate.

Calcinaio

serve ad eliminare tutte le parti inutili (pelo, epidermide, nervi, strato adiposo sottocutaneo, etc.) e a gonfiare le pelli per permettere un miglior assorbimento dei prodotti di concia. Tradizionalmente si ottiene questo risultato con un bagno di calce.

Scarnatura

i residui di carne ancora attaccate alla pelle e del tessuto adiposo vengono rimosse manualmente o meccanicamente, in modo da lasciare la pelle priva di qualunque residuo.

Spaccatura

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”.

Decalcinazione e Macerazione

la pelle, ancora impregnata di calce, viene lavata con acqua ed elementi decalcinanti; viene poi sottoposta a un bagno con particolari enzimi per eliminare ogni residuo di calce.

1- Beamhouse (preparation of hides)

Rinverdimento

le pelli ottenute come scarto dei mattatoi vengono sottoposte a un processo di salatura, che blocca la decomposizione e ne agevola il trasporto. Appena giunte in conceria vanno quindi lavate, liberate dalle impurità e reidratate.

Calcinaio

serve ad eliminare tutte le parti inutili (pelo, epidermide, nervi, strato adiposo sottocutaneo, etc.) e a gonfiare le pelli per permettere un miglior assorbimento dei prodotti di concia. Tradizionalmente si ottiene questo risultato con un bagno di calce.

Scarnatura

i residui di carne ancora attaccate alla pelle e del tessuto adiposo vengono rimosse manualmente o meccanicamente, in modo da lasciare la pelle priva di qualunque residuo.

Spaccatura

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”.

Decalcinazione e Macerazione

la pelle, ancora impregnata di calce, viene lavata con acqua ed elementi decalcinanti; viene poi sottoposta a un bagno con particolari enzimi per eliminare ogni residuo di calce.

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

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

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.

Slow Tanning in Tanks

It is the oldest tanning process in history. Hides are laid out on specific supports and immersed in big tanks filled with a solution of water and tannin in increasing concentrations. After a maceration in one tank, they are moved to the next one, and so on. A process that allows high quality but requires time and patience: it can last up to 8 weeks. Even nowadays, it is used by some tanneries to produce leather for shoe soles.

Fast Tanning in Drum

The drum is a machine introduced in the Nineteenth century. The hides are put inside this huge rotating container with a solution of water and tannin. The rotating movement allows a quicker absorption of the tanning agents, reducing considerably the time of the whole process in comparison to the vegetable tanning in tanks: from weeks to few days.

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?

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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

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2-Re-tanning

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3- Dyeing and fattening

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4-Second Setting Out and Drying

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Prima messa a vento

L’espressione tradizionale “messa a vento” indica in realtà una pressatura. Le pelli vengono pressate per far uscire l’acqua in eccesso. 

Riconcia

Prevede un secondo bagno in bottale con agenti concianti diversi o uguali da quelli utilizzati in precedenza.

Tintura e Ingrasso

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.

Messa a vento e asciugaggio

Una seconda pressatura elimina ogni residuo di acqua e umidità; le pelli sono quindi pronte per essere asciugate, secondo diversi metodi: semplice esposizione all’aria; passaggio in un tunnel di asciugatura con temperatura e umidità controllate, per microonde etc.

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:

Prima messa a vento

L’espressione tradizionale “messa a vento” indica in realtà una pressatura. Le pelli vengono pressate per far uscire l’acqua in eccesso. 

Riconcia

Prevede un secondo bagno in bottale con agenti concianti diversi o uguali da quelli utilizzati in precedenza.

Tintura e Ingrasso

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.

Messa a vento e asciugaggio

Una seconda pressatura elimina ogni residuo di acqua e umidità; le pelli sono quindi pronte per essere asciugate, secondo diversi metodi: semplice esposizione all’aria; passaggio in un tunnel di asciugatura con temperatura e umidità controllate, per microonde etc.

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

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.

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.

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