Tanning and Production
What Does It Mean to Tan Leather? What "Tanned" Really Tells You
Tanned leather is hide whose collagen has been permanently stabilized. See what tanning changes, how it differs from rawhide and what the word tells a buyer.
To tan leather means to treat a raw animal hide so that its protein structure changes for good. The hide stops rotting and becomes durable leather. "Tanned leather" is hide that has been converted to leather by a tanning agent, most often chromium salts or plant tannins.
The word tells you the hide has been stabilized. It does not tell you the grade, the layer, the color or the finish.
This page is part of our guide to leather tanning and production. It explains what the word means and what it promises a buyer. For the factory process itself, see how leather is produced.
"Tanned" has two meanings
Dictionaries give two senses of "tanned." One is skin that has darkened in the sun. The other is a hide "converted to leather by a tanning agent". This page covers the second.
The two senses share a history. The word comes from medieval Latin tannum, meaning oak bark, the old source of tanning material. The color tan is named after undyed vegetable-tanned leather.
What tanning changes inside a hide
The leather-making part of a hide is the corium, its collagen layer. The beamhouse removes the hair and epidermis on one side and the flesh and fat on the other.
Tanning then works on that collagen:
- Plant tannins bind to the collagen and coat it. The fibers become less water-soluble and harder for bacteria to attack.
- Chromium(III) salts cross-link the collagen. The hide turns a greyish blue, called "wet blue".
The change is permanent. The hide becomes more durable and much less likely to decompose.
How you can measure it: shrinkage temperature
Shrinkage temperature is the point at which a hide shrinks when heated, a measure used in leather conservation research. The more tanning material is fixed in the hide, the higher it goes, and a higher figure means a more stable material.
So "tanned" is not a vague word. It describes a change in the hide's stability that a lab can measure.
| Material | Shrinkage temperature |
|---|---|
| Untanned hide | Below 65 °C (149 °F) |
| New vegetable-tanned leather | 70-85 °C (158-185 °F), depending on the tannin group |
| Chrome-tanned leather | Over 100 °C (212 °F) |
Tanned leather vs rawhide
[Rawhide](https://en.wikipedia.org/wiki/Rawhide_(material)) is the same hide without the tanning. The hair, meat and fat are removed, then it is stretched and dried.
A hide can be made soft without being tanned, by rubbing, stretching and working fat into it. Unless it is regularly given more fat or oil, it goes back to rawhide, especially after getting wet.
One naming trap: "rawhide" laces sold for boots are usually tanned leather.
| Column 1 | Rawhide | Tanned leather |
|---|---|---|
| Tanning agent | None | Chrome, plant tannins or another agent |
| When dry | Hard and translucent | Flexible, depending on tannage and finish |
| When wet | Softens and stretches | Chrome leather keeps its shape better than veg tan |
| Decay | Not stabilized | Much less likely to decompose |
The main ways to tan
Speed varies a lot. Chrome tanning takes about a day. Vegetable tanning took about six weeks in all at one US tannery and about 12 months in one UK oak-bark pit tannery.
For each method in depth, see what is vegetable-tanned leather? and brain tanning: how the process works.
| Method | Tanning agent | What it gives |
|---|---|---|
| Chrome | Chromium(III) salts; hide turns wet blue | Supple leather; about 85-90% of leather made today |
| Vegetable | Tannins from bark and leaves | Firmer leather for belts, luggage and tooling |
| Wet white | Aldehydes or aluminium, zirconium, titanium or iron salts | Off-white leather |
| Tawing | Alum and aluminium salts, often with egg yolk or flour | Alum alone shrinks the skin and leaves it hard |
| Brain or oil tanning | Emulsified oils from brains, eggs or soap and oil, plus smoke | Soft, washable buckskin |
Is brain-tanned buckskin really "tanned"? Sources disagree
This is the edge case that shows what the word means.
- One view: brain-tanned leathers such as buckskin are made with emulsified oils and count as a tannage.
- The other view: the outdoorsman Horace Kephart wrote that true Indian-tanned buckskin is "not tanned at all." To him it was a raw skin softened by breaking up its fibers, then treated with brains and smoke.
Both views agree on the role of smoke. Formaldehyde from wood smoke gives the hide some resistance to microbes and water. Kephart notes that smoked buckskin goes a little stiff after wetting but softens again when rubbed.
We don't settle this question here. In practice, it means "tanned" can cover very different chemistry. If you want to make buckskin yourself, see how to brain-tan a deer hide.
What tanning is not: dyeing and finishing
Tanning is only one of four stages in a tannery: beamhouse, tanning, post-tanning and finishing.
- Tanned but not finished. Wet blue is chrome tanned but still undyed and pale blue. "Crust" is leather that has been tanned with no further finishing.
- Color comes later. Dyeing and fat-liquoring happen in post-tanning.
- The surface comes last. Finishing adds coats or wax and presses or irons the leather.
So "tanned," "dyed" and "finished" are three separate claims. A hide can be the first without being the other two.
What "tanned" on a label tells a buyer
- It confirms the hide is leather, not rawhide. That is all it confirms on its own.
- The method changes how the leather behaves. Chrome leather is more supple and copes better with water. Vegetable-tanned leather darkens with water and can shrink and harden if soaked and dried.
- It is not a grade. At one US vegetable tannery, every grade is tanned the same way, so the grades differ in blemishes and yield, not tannage.
- Names can mislead. Some leather sold as "buckskin" is chrome-tanned sheepskin dyed to look like it.
If the tanning method matters to you, ask the maker which one was used. For grades and layers, see our guide to leather types, grades and quality.
Choosing finished leather
On Leather Collection jacket pages, each made-to-order jacket names its animal: cowhide, sheepskin, lambskin or goatskin. The pages do not state whether the leather is chrome or vegetable tanned. Ask before you order if that matters for your use.
A short history of tanning
Tanning is very old. It was being done at Mehrgarh, in present-day Pakistan, between 7000 and 3300 BCE.
Early tanners removed hair with urine, lime or controlled rotting. They softened hides by pounding them in dung or soaking them in brain solution. Chrome tanning came much later, in the second half of the 19th century.
Related pages
- What is a tannery?: the plant where tanning happens.
- How to tan hides into leather: a home method, step by step.
- Vegetable-tanned leather hides: what to know: buying hides from a veg tannery.
FAQ
What does "tanned" mean?
For leather, it means the hide has been converted to leather by a tanning agent. For skin, it means darkened by the sun.
What is tanned leather?
It is animal hide whose collagen has been permanently stabilized with chromium salts, plant tannins or another agent, so it no longer rots like raw skin.
What is leather tanning?
It is the process of treating animal skins and hides to produce leather, and it happens in a tannery.
How long does it take to tan leather?
Chrome tanning takes about a day. Vegetable tanning takes weeks to months, depending on the method.
Can tanned leather turn back into rawhide?
Tanning permanently changes the hide's protein. A hide that was only softened with fat, without tanning, can go back to rawhide if it is not re-oiled.
LeatherGuru Editorial Team
LeatherGuru articles are researched from published sources, cited in the text, and reviewed before publication.