How Leather Is Made
Leather is animal hide that has been chemically stabilised so it will not decay. That stabilisation is tanning, and everything else in the process is preparation for it or refinement after it.
The whole sequence runs: select the hide, strip it back to clean collagen, tan it, colour and soften it, finish the surface. Where a tannery spends its time within that sequence decides what kind of leather comes out.
The raw hide
Hides are a by-product. Cattle are raised for meat and dairy, and the hide would otherwise be waste.
Quality is decided before the tannery sees anything. Climate matters, and hides from cooler regions tend to have denser collagen and a tighter grain. So does the animal's life: scars, insect bites and barbed wire all remain visible in a hide that will be finished without correction.
Hides are cured with salt or chilled immediately after slaughter, because untreated hide begins to spoil within hours.
Preparing the hide
Before tanning can happen the hide has to be reduced to clean collagen fibre. This is the least discussed stage and it takes days.
The hide is soaked to restore water lost in curing, then treated with lime to loosen the hair and open the fibre structure. Hair and remaining flesh are removed. The lime is neutralised, and the hide is treated with enzymes that break down the material binding the fibre bundles together.
How far that opening is taken is one of the largest decisions in the process. A thoroughly opened hide will be supple. An under-opened one stays firm whatever follows, and no amount of oil or finishing corrects it.
This is also the stage where a hide is split. A thick hide is passed through a splitting machine that separates it horizontally: the upper layer carries the grain and becomes full grain or top grain leather, and the lower layers become split.
Tanning
Tanning binds agents into the collagen so the fibre can no longer decay. There are two dominant routes and they produce materially different leathers.
| Vegetable tanning | Chrome tanning | |
|---|---|---|
| Agent | Plant tannins from barks such as chestnut and mimosa | Chromium salts |
| Time | Weeks | Hours |
| Result | Firm, with structural memory | Soft and pliable immediately |
| Colour | Warm natural tan | Pale blue-grey before dyeing |
| Ages | Darkens and develops a patina | Wears rather than matures |
| Share of world production | Small | The large majority |
Vegetable tanning works the hide through progressively stronger tannin liquors, in pits or in wooden drums, over weeks. The tannins are polyphenols drawn from plant matter, and they bind through the full thickness of the hide. They are also light sensitive, which is why only vegetable tanned leather can develop a patina.
Chrome tanning achieves stabilisation in hours using mineral salts, and it dominates world production for that reason. It produces a softer, more uniform, more water-resistant leather that will never patina, because there are no plant tannins present to respond to light.
Our own Perpetual Leather is vegetable tanned over forty days in wooden drums with chestnut and mimosa extracts.
Retanning, dyeing and fatliquoring
Three things happen after tanning, and they decide almost everything about how the finished leather feels.
Retanning adjusts the character, adding fullness or firmness.
Dyeing introduces colour. Transparent dyes that saturate the full thickness leave the grain visible and produce aniline leather. Pigments applied to the surface produce semi-aniline or pigmented leather, covering the grain to the extent they are used.
Fatliquoring works oils into the fibre structure so the fibres slide against one another rather than binding as the hide dries. It is a major contributor to suppleness, and it is the reason a well-made leather arrives with most of the oil it needs already in it.
Drying and mechanical work
The stage that decides handle, and the one most accounts leave out entirely.
How a hide dries changes what it becomes. Leather dried under tension comes out firmer than leather dried loose, because the fibres set in the position they were held in.
After drying, leather is worked mechanically. Staking flexes it repeatedly to break the bonds that formed as it dried. Milling, tumbling the leather in a drum for hours, softens it further and rounds the grain. How much of this a hide receives is a deliberate decision, and two hides identical up to this point can leave the tannery with completely different handles.
This is why softness is not a property of the tannage. A vegetable tanned hide can be made very soft here, and a firm leather is firm partly because it was not given this treatment.
Finishing
The final stage decides the surface. It can be almost nothing, as on an aniline leather where the grain is left exposed. Or it can be a multi-layer film: a sealing coat, a pigmented base coat and a topcoat, built up over a surface that has usually been sanded and corrected first.
A texture may also be pressed in with a heated plate, producing pebbled or Saffiano. Where that pressing falls in the finishing sequence varies between tanneries.
The important thing to understand is that a heavy finish is a separate material sitting on the hide. How long it lasts depends on how well it was made and how well it bonded, and that is a question about the finish rather than about the leather beneath it.
How long it takes
Chrome tanning can move a hide from raw to tanned in a day. Vegetable tanning takes weeks, and in the slowest traditions considerably longer.
That difference is the whole economic argument, and it is why roughly nine tenths of the world's leather is chrome tanned.
From tannery to finished piece
The tannery delivers hides. What happens next is a different craft: selecting which parts of the hide go where, cutting, skiving the edges thin enough to fold, assembling, and stitching.
Where a panel is cut from matters enormously. The bend along the spine has the most uniform fibre in the hide and holds a shape. The belly is loose and will not.
Related reading
Types of leather · Leather patina · Saddle stitch · Aniline leather · Vachetta leather · Buffalo leather · Mushroom leather
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