Metal-Free and Chrome-Free Leather: Wet-White Tanning and What the Label Means

Chrome-free leather is tanned without chromium salts, using plant tannins, synthetic tannins or aldehydes. "Wet white" is the aldehyde route and gives off-white leather. "Metal-free" is a looser label: the sources we read do not agree on one definition, and wet white can itself be made with metal salts.

This page is part of our guide to leather tanning and production. It covers what the labels mean and where the trade-offs sit. Most of what follows comes from trade articles and sellers, and we say so where it matters.

What each label means

A repair company says aldehyde wet whites contain no chromium. Wikipedia lists metal-salt wet whites. Both can be true of different leathers, which is why the label alone is not enough.

How wet white is made

A tanning-chemicals maker says most chrome-free leathers are pre-tanned with modified glutaraldehyde. A 2002 trade article describes the idea: the hide is shaved while largely untanned, then tanned with glutaraldehyde and alcohols. A repair company adds oxazolidine as another aldehyde, and says formaldehyde was once used and dropped.

Chrome tanning works differently: chromium(III) salts cross-link the collagen and leave the hide greyish-blue ("wet blue"). For that process, see chrome-tanned leather.

Plant tannins are the other chrome-free route. Our page on vegetable-tanned leather covers it.

How it performs

The evidence is thin. These are trade articles and sellers, not independent tests.

• Heat. A 2002 article reports a shrinkage temperature of 70-75 C (158-167 F) for a wet-white pretannage, enough for shaving. In a 2003 trial by a tanning-chemicals company, an aldehyde-polymer wet white reached 80 C (176 F), against 82 C (180 F) for glutaraldehyde.
• Color. The same trial found the polymer leather ivory white and the glutaraldehyde leather yellowish. The glutaraldehyde leather fell below the light-fastness requirement, while the polymer leather just met it. The 2002 article links yellowing to ammonium salts, and says ammonium-free deliming addresses it.
• Feel and wear. A repair company says wet whites are very soft and washable, but stretch or tear easily and have a finish less durable than chrome-tanned leather. It says heat and water do the most damage.
• Plant and synthetic routes. A shoe retailer says chrome-free leather may feel stiffer at first and cost more.

Why "metal-free" turns up in car and child-product specs

Two sources tie the label to chromium(VI). A tanning-chemicals maker says demand for metal-free shoe uppers and leather goods is driven by the potential risk of chromium(VI) forming in accessories. A 2003 trade article says car upholstery must meet strict combustibility and toxicity requirements, which it links to chrome content.

The same trade article says automotive is the largest consumer of chrome-free leather. A repair company says some car makers use wet whites for interiors and that they appear in children's shoes.

We have not read a car maker's specification or a children's-product standard, so we cannot say what any of them requires.

Does chrome-free mean risk-free?

No source we read proves that. A shoe seller says chrome-free leather "eliminates the risk entirely", but its page gives no evidence for that claim.

What the evidence does say: chromium(VI), not chromium(III), is the form the EU restricts in skin-contact leather, at 3 mg/kg. Chrome-free describes the tannage, not a test result for a given jacket. Other substances, such as glutaraldehyde, bring their own drawbacks, such as itching and a bad smell, as a chemical company's author notes. For the chromium side, see chromium in leather.

What to ask a seller

1. Which tannage does the label mean: plant, synthetic, aldehyde, or metal salts?
2. If it says "metal-free", what does the maker count as a metal?
3. Is there a test report, and is it for this batch?

Leather Collection's own guide says chrome tanning is the dominant method today and that tannery chemical control matters. Its product pages do not state the tanning method. For its discussion of tanning and tannery audits, see Leather Collection's guide to tanning and tannery standards.

For what the word "tanned" tells you, see what does it mean to tan leather. For finishes added after tanning, see treated leather. For the footprint question, see how environmentally friendly leather is.

FAQ

What is chrome-free leather? Leather made without chromium salts, using plant tannins, synthetic tannins or aldehydes.

What is wet white leather? Off-white leather from an alternative tannage, most often with aldehydes, though metal salts also appear in the definition.

How can you tell if leather is chrome or vegetable tanned? We found no reliable home test, and we do not recommend burn or solvent tests. Ask the seller what the tannage is.

Is leather sustainable? This page does not answer that. See how environmentally friendly leather is.