Leather is not a surface

A finished leather offers itself to the eye as a surface. It can be smooth, matt, glossy or velvety; it can carry a uniform colour or show veining and differences of tone. Under the hand it can feel firm, yielding, dry or almost waxy. It is easy to believe that the tanner’s craft consists in producing that appearance.

When the hide arrives at the tannery, none of those qualities exists yet. The material is heavy, wet or salted, folded over on itself and ragged along the edges. Its thickness varies, some areas are denser and others looser, and it carries the marks of its own origin, of the flaying, of the curing and of the journey.

Two hides can take the same colour and not become the same material. One absorbs quickly, the other resists. One holds an even surface, the other shows scars and veining that finishing can soften, bring out or make more visible still. Colour can level what is seen; it cannot make identical what, inside, never was.

The craft begins below the surface.

The material comes from another supply chain

The tannery does not produce raw hide: it receives it. The cattle, sheep, goat and pig hides and skins used by the tanning industry normally come from the food supply chain and are classified as animal by-products. Tanning turns into a material something that, with no other use, would have to be handled and disposed of.

That does not make what came before irrelevant. A hide being a by-product does not cancel the conditions of rearing, the transport, the slaughter, the precision of the flaying and the effectiveness of the curing. A cut made during flaying reduces the usable area; curing done too late can compromise the structure before the damage is visible. A scar belongs to the life of the animal; a tear made by a blade belongs to the process.

Traceability serves this purpose too: to establish how much the tannery knows about its own material, the supplier and the abattoir, and not merely to state a country of origin. The tanner cannot correct a hide’s history after the fact, only know it well enough to decide whether and how to work it.

A hide just taken from the animal is putrescible biological matter: to stop it degrading quickly it has to be chilled, salted or cured by some other method compatible with transport. Salt reduces the water available for microbial activity and slows deterioration. It does not improve the material: it does not close a cut, it does not rebuild a damaged fibre and it does not cancel time spent in the wrong conditions.

When a batch arrives, species, size, thickness, curing and damage are all checked. A hide suited to a soft leather-goods article is not necessarily the right one for a belt, a shoe upper, an upholstery leather or a sole leather. Selecting does not mean separating the good from the bad: it means understanding which transformation that material can take. The store is the first place where what a hide can become is decided.

Before tanning, material has to be removed

Tanning proper comes after a long preparation. First the hide has to recover the water lost during curing: in soaking it is immersed and moved in water together with products that remove salt, dirt and substances that must go no further. This is not a simple wash. Rehydration means bringing the fibre structure back to a condition in which it can be worked evenly; if some areas stay drier, they will react differently later on.

Hair and epidermis are then removed, when the finished product is not meant to keep them. In conventional processing this stage can use lime and sulphides, at concentrations and for times that have to be controlled to obtain the necessary effect without damaging the grain. Fleshing takes away the fat and residual tissue left on the flesh side after flaying. Splitting can divide a very thick hide into two layers. Deliming removes the products used in the liming and reduces the swelling, while enzymatic bating prepares the structure for the softness required.

These operations are often described as a preliminary and unglamorous corner of the tannery. In fact they settle much of what will still be possible. Insufficient cleaning can obstruct the penetration of the products that follow; treatment that is too aggressive can weaken the structure; imprecise fleshing leaves differences; badly set splitting reduces the thickness where it should have been kept. Before adding colour, softness or protection, the tanner has to remove everything that would stop the hide receiving them.

Transformation begins by subtraction.

The grain is not a printed pattern

In tannery language the grain is the outer part of the hide, the side where the hair and the follicles were. Its pattern is not a decoration applied at the end: it belongs to the original structure of the material. When a hide is split, the upper layer keeps the grain; the lower one is called the split, and it can go to different processes and different products.

This does not make the split unusable material: it can become suede, it can be coated or it can take finishes capable of producing articles with precise characteristics. It does not, however, have the original fibrous surface of the upper layer, and it should not be described as though it were the same thing. The words suede and nubuck also describe different processes: suede is normally obtained by working the flesh side or a split, while nubuck comes from lightly buffing the grain side, which produces a velvety surface while keeping the structure of the outermost part. To the eye they can look alike. Their construction does not.

A leather that keeps its natural grain shows scars, wrinkles, follicles and differences more readily; a corrected or coated surface can look more uniform and offer more protection. What decides is not a moral hierarchy but an end use: a bag designed to change over time may call for a lightly covered surface, while a seat subjected to thousands of rubs, to light, heat and cleaning needs a more structured protection. The craft consists in declaring what has been done and in doing it consistently with what the object will have to withstand.

Tanning makes a transformation irreversible

Raw hide is largely a network of collagen fibres. That structure has strength and elasticity, but in its natural state it stays vulnerable to water, to heat, to micro-organisms and to decay. Tanning changes the way the fibres interact: the tanning agents penetrate the hide and stabilise the collagen structure, making it non-putrescible and able to withstand processing, drying and use.

Impregnating the surface is not enough: the agent has to reach through the thickness of the hide and distribute itself in a way compatible with the intended result, and only then be fixed into the structure. Penetration and fixation are not the same thing. If the tanning agent reacts too quickly in the outer zones, uniformity in the inner parts becomes harder to obtain; if it penetrates without fixing, stabilisation stays incomplete and more of the product ends up in the spent bath.

So the tanner controls concentration, the amount of water, temperature, pH, time and the movement of the drum. The cylinder turns, but it does not know what is happening inside the hide: it runs the programme it was set and goes on running it even when the material is answering differently from what was expected. The machine produces movement; the craft decides when that movement has achieved a sufficient transformation.

Vegetable does not mean leaves left in the pits

Vegetable tanning uses tannins extracted from plant materials. In the Tuscan district, chestnut, mimosa and quebracho extracts are common, used on their own or in blends chosen for the structure, the colour and the behaviour wanted. Today those tannins reach the tannery as liquid extracts, concentrates or powders: they are not necessarily leaves and bark left to steep with the hides until nature decides the work is over.

The plant origin of the tanning agent is real. So is the technology needed to extract it, dose it, drive it in, fix it and handle what stays in the bath. Vegetable tanning can be carried out in pits, in drums or through combined systems, and how long it takes changes with thickness, article, bath concentration and method. Sole leather is not built like a soft leather for a bag, and a thin cowhide does not require the same process as a heavy material for saddlery.

Nor does the word vegetable mean the absence of chemistry. Tannins are chemical substances made by plants, they interact with collagen through chemical and physical phenomena, and the spent baths contain organic matter that has to be handled and treated. The natural origin of a product does not remove responsibility for the process.

Chromium III and chromium VI are not the same thing

Chrome tanning normally uses salts of trivalent chromium, written as chromium III. The technology gives leathers that are stable, heat-resistant, relatively light and able to carry a wide range of colours. Hexavalent chromium, or chromium VI, is a different and dangerous chemical species: it is not used deliberately as an agent in ordinary chrome tanning, but it can form through oxidation of chromium III when the process, the formulation, the substances used or the storage conditions are not properly controlled.

The distinction should become neither a blanket alarm nor an alibi. Saying simply “it contains chromium” does not describe which chemical form is present; saying that chromium VI is not added is not enough to show that it cannot form. European legislation prohibits the marketing of leather articles intended to come into contact with the skin when the concentration of chromium VI reaches or exceeds the limit set. So the tanner has to know not only what goes into the drum, but also the reactions that could take place later, during production, storage and the life of the finished object.

In the same way, a leather described as chrome-free is not a leather made without chemicals. It may use vegetable tannins, synthetic agents, aluminium, zirconium, modified aldehydes or different combinations, and each produces its own properties, consumption, risks and treatment needs. The useful question is how it was used, how effectively it entered the leather and what came out of the process.

Thickness is a design decision

After tanning the leather is stable, but it is not finished. It has to be pressed to squeeze out part of the water it absorbed, it can be split again, and it is shaved to reach the required thickness. Shaving produces thin shavings and reduces the differences across the surface. It looks like a simple adjustment; in fact it settles an essential part of the future behaviour.

A belt needs body and resistance to stretching; a shoe upper has to be moulded without tearing; a glove has to follow the movement of the hand; a soft bag has to give without losing its shape altogether. More thickness does not automatically mean more quality: a leather that is too heavy can be unsuitable for a seam, hard to fold or out of proportion with the object, and one that is too thin may not hold the pull, may deform or may show the marks of the structure beneath.

The value lies in consistency: bringing a naturally irregular material to a thickness even enough without taking away what the use will need. Every pass of the blade removes a possibility, and material once shaved cannot be put back.

Colour has to go in before it can show

Neutralisation, retanning, dyeing and fatliquoring can follow the tanning. Neutralisation adjusts the acidity left behind; retanning changes fullness, firmness, elasticity and the behaviour of the different zones, and it can use agents other than those of the main tannage, building properties the first would not have produced.

Dyeing introduces colour into the structure and should not be confused with surface finishing. A dye dissolved in the bath penetrates the fibres; a pigment applied during finishing forms instead, together with the binders, a more or less covering layer on the surface. They are different tools.

The choice depends on the article; the difficulty lies in repeating it. Two hides from the same batch can absorb differently because of thickness, fibre density and earlier processing, and the same dosage does not guarantee the same tone. The colourist has to watch the bath, draw samples, compare the shade under the right light and correct without losing the other characteristics. A colour has not succeeded merely because it looks good while the leather lies still on the table: it has to stay consistent after drying, finishing, folding, rubbing, stitching and use.

Fatliquoring then distributes through the structure substances that contribute to softness, flexibility and handle, and this stage too is not a matter of applying oil in general: type, quantity and distribution have to be compatible with the tanning agent, the dyeing, the drying and the end use. A leather can be soft and at the same time empty, or firm and resist folding too much.

Mechanical operations follow the drying: staking makes the leather more flexible, dry milling in the drum softens it and brings out the grain. The final handle comes from the interaction of chemistry, water, drying and mechanical movement. There is no softness that is best in the absolute. The craft does not look for the softest possible material, it looks for the right behaviour.

Finishing is not necessarily a disguise

Finishing covers the operations carried out on the dry surface to change its appearance and its performance: it can add colour, uniformity, gloss, resistance to water, to dirt and to scratches, and it can be transparent or build a more covering pigmented film. In the commercial account of leather a lightly finished surface is presented as inevitably more truthful, while heavier coverage is treated as though it served only to hide mediocre material. Sometimes it does. It is not a rule.

A transparent finish requires a surface able to stay visible and accepts that the marks become part of the identity of the product; a pigmented finish allows more uniformity and can offer the protection that heavy-wear uses need. The choice becomes a problem when it is concealed, or when the surface promises something the structure cannot keep. An embossing can imitate a natural grain; it cannot create the fibre density that grain is supposed to stand for. A finish can cover a mark; it cannot rebuild a weak area.

A perfect surface does not prove that the leather has been perfectly made: it proves only that, at that moment, the surface looks perfect.

The reverse holds as well. A natural leather can show wrinkles, differences of grain, small scars and variations of colour, and those marks can become part of the language of a product. But not everything irregular deserves to be celebrated. A deep cut does not turn into a merit because it testifies to the human hand, and an area of damaged grain does not gain value by being called lived-in. A dye that bleeds, a finish that lifts or a surface that cracks early are not patina. They are problems.

Patina is a transformation produced by use, by light and by care, particularly visible in some lightly covered vegetable-tanned leathers: it can darken the colour and build a surface different from the original one. But a material designed to develop it has to go on doing its job: expected change and degradation are not the same thing. The craft also consists in drawing that line, leaving visible what belongs to the material and declaring what compromises the product, without turning every defect into a poetic story.

At Santa Croce, a hide crosses a district

In the Tuscan tanning district, production is not necessarily held inside a single company. The activity has grown up between Santa Croce sull’Arno, Ponte a Egola, San Miniato and the surrounding municipalities, through a network of tanneries, workshops, chemical suppliers and research centres. Some firms run a wide cycle starting from raw hide; others begin from already tanned semi-finished stock such as wet-blue, or put stages such as splitting, shaving, drying or finishing out to specialist operators.

A hide can therefore pass through several plants before it is finished. That does not make it any less a craft: it makes it essential that every stage be identified, coordinated and compatible with the next. Whoever shaves has to know what thickness the finishing will need; whoever dyes has to know how the previous tannage behaves; whoever finishes has to respect the approved handle, colour and grain. The district model replaces the image of the isolated master with a collective competence: not one person in front of a pit, but a sequence of specialisations. Quality does not depend on a hide staying under the same roof: it depends on its not losing its identity as it crosses several.

Before running a batch the tannery makes samples. The customer judges colour, handle, thickness, grain and strength, and can ask for minimal corrections that, in the material, force several stages to be reworked: a deeper tone changes the relation between dyeing and finishing, a softer handle imposes a different retannage. The approved sample becomes a promise, and production has to repeat it on hides that will never be identical to the one it was born on. This is where contemporary craft shows its hardest form: not in the unrepeatable piece, but in the ability to obtain a recognisable result from materials that keep arriving with differences.

The hand and the eye are not enough. Finished leathers can be put through physical, chemical and fastness tests: tear strength, flex resistance, rub fastness, colour stability, the presence of substances subject to limits. A leather can have a perfect colour and transfer it onto a light fabric, be soft and tear near the seam, look uniform and show cracks after repeated flexing. The laboratory does not contradict the craftsman’s judgement: it forces it to survive beyond the first look.

Sustainability is not a shade of green

Tanning uses water, energy and chemicals, and it produces waste water, emissions, sludge, trimmings, fleshings, hair, dust and spent baths. The quantity and nature of the outputs change with the material, the type of tannage, the technology and the article. There is no zero-impact process. Vegetable tanning uses agents of renewable origin, but its baths can carry a high organic load and have to be treated. Chrome tanning can use small quantities of tanning agent and produce light, stable leathers, but it demands rigorous management of the baths, of the residues and of the risk of chromium VI forming.

The Tuscan district has developed centralised treatment plants, systems for handling sludge and a consortium dedicated to recovering residual chromium from specific tanning baths, which is purified and returned to the companies for reuse. These are important pieces of infrastructure. They do not automatically turn every leather made in the district into a sustainable material, which has to be measured through consumption, emissions, recovery, durability and chemical compliance.

Vegetable describes the origin of the tanning agent. Chrome-free describes the absence of chromium in the declared system. Recycled describes the recovery of a material. None of these words, on its own, tells everything that happened. A serious environmental declaration does not pick the most reassuring term: it shows figures, boundaries and responsibilities.

Technology does not remove the hand. It moves it

The contemporary tannery uses programmable drums, automatic dosing systems, presses, shaving machines, drying plant, finishing booths and instrumental laboratories. It does not necessarily look like the dark room with a few wooden vats that nostalgic communication keeps offering. This does not mean the craft has disappeared: it means the hand comes in at a different point, where the programme to be set is decided, the parameters are read and someone recognises when the machine is correctly repeating the wrong operation.

A pump doses exactly the quantity programmed, even when that quantity does not suit the batch. A drum keeps to the cycle it was given, even when penetration is already sufficient. A booth lays down a uniform finish, even when the formulation covers too much. Automation increases the precision of what has been decided; it does not guarantee that the decision was right: the material always brings in new variables.

The surface has to go on working

A leather is not made to lie flat on a tannery table. It will become something else: it will be cut, skived, laminated, glued, stitched, folded and assembled, and it will meet the pressure of a buckle, the heat of a car, the sweat of a hand, the weight of a bag, the tension of a shoe or the rubbing of a seat. The tanner has to imagine those stresses while the leather still has no final shape.

Properties do not hold in the abstract. A resistant finish can protect an upholstery leather and be excessive on a small leather good that has to keep depth and softness: the same property can be a quality in one product and a fault in another. That is why the tanner does not build a fine leather in general, but a material able to face one precise use.

The customer sees the colour. The leather-goods maker sees the cutting. The shoemaker sees the fold. The upholsterer sees the usable area. The tanner has to see them all before the object exists.

During processing a hide loses a great deal: salt, hair, epidermis, fat, residual tissue, water, ragged edges and part of its own thickness. It receives tanning agents, colour, fatliquors and finishes. Yet it does not become an entirely new sheet: it keeps its fibre structure, its irregular shape, the differences between one zone and another and some of the marks gathered before it entered the tannery.

Competence does not consist in erasing every difference. It consists in making it compatible with a function. The tanner has to obtain repeatability without pretending the material is standard, build performance without necessarily erasing the origin, decide how much to leave visible and how much to protect. Leather is not a surface on which an appearance is applied: it is a structure that has to go on working after changing its nature.

The colour reaches the eye. The craft stays inside.