Tanning and Production
What Is a Tannery? Inside the Plant That Turns Hides into Leather
A tannery turns hides into leather. See its four stages, the chemicals used, why tanneries smell, UNIDO yield figures and how to judge one.
A tannery is the plant where animal hides and skins are processed into leather. Inside, hides are cleaned and unhaired in the beamhouse, tanned with chromium salts or plant tannins, then dyed, oiled, dried and finished. The tannery decides much of how the leather in a jacket, belt or bag will look, feel and age.
This page is part of our guide to leather tanning and production. It covers what a tannery does, what goes in and comes out, why tanneries smell, and how to judge one.
What a tannery does, stage by stage
UNIDO, the UN's industrial development agency, splits tannery work into four stages.
Curing usually happens before the tannery. Hides are salted, brined or chilled so bacteria cannot spoil them, and UNIDO notes this is normally done before they reach the tannery.
For each operation in order, see how leather is made: from raw hide to finished material.
| Stage | What happens | Typical inputs |
|---|---|---|
| Beamhouse | Soaking, liming and unhairing, fleshing, deliming, bating, pickling | Water, lime, sodium sulphide, ammonium salts, enzymes |
| Tanning | Tanning agent bonds to the hide's collagen | Chromium(III) salts or plant tannins |
| Post-tanning (wet work) | Splitting, shaving, retanning, dyeing, fat-liquoring, drying | Dyes, oils, waxes |
| Finishing | Surface coats or waxes, pressing or ironing, grading | Binders, pigments, solvents |
Not every tannery does every step
Tanneries split the work. Some take raw hides only to wet blue, the pale blue state after chrome tanning. Others buy wet blue or "wet white" and only dye and finish it, as the Leeds suede tannery Charles F. Stead does.
Full-cycle plants are now rarer. Horween in Chicago says it is one of only a handful of US tanneries that still take hides from the raw, cured state to finished leather.
Why it matters to a buyer: "tanned in Italy" may describe only part of the work. Ask where the hide was tanned and where it was finished.
| Tannery type | Starts with | Ends with |
|---|---|---|
| Raw to wet blue | Salted or chilled hides | Wet blue |
| Wet blue to finished | Wet blue or wet white | Finished leather |
| Full cycle | Raw hides | Finished leather |
What goes in and what comes out
In UNIDO's model tannery, one tonne of salted cattle hides becomes about 255 kg (about 560 lb) of finished leather: 195 kg of grain and 60 kg of split. Only 53% of the hide's leather-making collagen and 15% of the chemicals bought end up in that leather.
The rest leaves as hair, flesh, fat, trimmings, shavings and wastewater. UNIDO notes that cleaner processes can turn some of these solid wastes into by-products. These model figures date from 2000, and real tanneries differ.
| Per tonne of salted hides (UNIDO model) | Amount |
|---|---|
| Finished grain leather | 195 kg; 138 m² (about 1,490 sq ft) |
| Finished split leather | 60 kg; 60 m² (about 650 sq ft) |
| Water used | About 40 m³; modern plants often below 25-30 m³ |
What chemicals are used in a tannery?
- Salt for curing and in the pickle.
- Lime and sodium sulphide to loosen hair and open the fibers. Liming effluent is the most polluted wastewater in the plant.
- Ammonium salts and enzymes to delime and bate.
- Chromium(III) salts in chrome tanning, the method behind about 85-90% of leather.
- Plant tannins such as mimosa and quebracho in vegetable tanning.
- Dyes, oils, waxes and solvents in post-tanning and finishing.
Chromium(III) is much less toxic than chromium(VI), but poor waste treatment can create chromium(VI). The EU bars leather articles that touch the skin if they contain 3 mg/kg or more of chromium(VI).
What does a tannery smell like?
Tanneries smell for three main reasons, according to IULTCS, the international union of leather chemists:
- Rotting organic matter. Hides, trimmings and fleshings putrefy if they are stored too long or too warm.
- Hydrogen sulphide and ammonia. Hydrogen sulphide smells of rotten eggs. It is released when sulphide liquors are acidified, for example in deliming.
- Solvents. Finishing can release solvents such as butyl acetate and acetone.
The smell is also a safety warning. Above 200 ppm, hydrogen sulphide can no longer be smelled, and 200 ppm for one minute can cause loss of consciousness. That is why IULTCS calls portable gas detectors essential.
Tanneries have always smelled. Historically, tanning was an "odoriferous trade" pushed to the edge of town.
How big are tanneries?
Size varies widely.
Horween processes about 4,000 cowhides and 1,000 horsehides in a typical week. Pakistan's trade development authority counts about 800 tanneries nationwide. Italy accounts for about 67% of the value of European leather production.
How to judge a tannery
You will rarely visit one, but you can check a few things.
LWG medals run Gold, Silver, Bronze and Audited. A plant must reach its medal in every section, so the weakest section sets the rating.
Poorly run tanneries have caused serious harm. A 2012 Human Rights Watch report on Hazaribagh, Bangladesh, described untreated effluent and sick workers, including children. For more on this, see how environmentally friendly is leather?.
| Check | What it tells you |
|---|---|
| Leather Working Group (LWG) certificate and medal | The plant passed an audit covering effluent, chemicals, chromium VI and traceability |
| Which site is certified | LWG certifies the facility that made the leather, not the product |
| Traceability score | LWG scores how much material traces back to a slaughterhouse; it does not audit farms |
| Tannage stated | Tells you chrome or vegetable; the store pages we checked often don't say |
Where tanneries fit in the leather you buy
The tannery sets tannage, thickness and finish, but not the grade on its own. At one US tannery, every grade goes through the same tan yards, and grades differ only in blemishes and yield. Read leather grades explained for how hides are sorted.
Made-to-order jackets from Leather Collection name the animal on each product page, but the category pages do not state the tanning method. Ask before you order if tannage matters to you.
Related pages
- How leather is produced: the chain from farm to finished leather.
- How suede is made: what a suede tannery does differently.
- Vegetable-tanned leather hides: what to know: buying hides straight from veg tanneries.
FAQ
What is a tanner's job?
A tanner runs the processes above: soaking, liming, tanning, dyeing and finishing hides into leather.
Why did tanneries smell?
Rotting hide waste, hydrogen sulphide and ammonia from unhairing and deliming, and later solvents from finishing. Older methods also used urine and dung.
Do cows need to be killed for leather?
European tanners say their leather comes from animals reared for food or hunted, and that the hide is a residue they recover. Whether leather is only a by-product is disputed.
Veganuary argues leather is a profitable trade in its own right. See is leather ethical?.
How do you tan a hide?
Industrial tanning follows the stages above. For a small-scale method, see how to tan hides into leather.
LeatherGuru Editorial Team
LeatherGuru articles are researched from published sources, cited in the text, and reviewed before publication.