How shoe leather is tanned

Vegetable tanned leather ready to be crafted.
Image source: benedix

Have you ever wondered why one pair of shoes lasts and lasts, while another falls to pieces as soon as it’s introduced to the first seriously wet day of autumn? Clearly not all leather is created equal. But how do you tell the difference between quality shoe leather and its poor relation? The answer? It’s all about the tanning.

Tanning

Early leather shoes were crudely made.
Image source: Shevtsova Julia

Tanning is the process by which leather is treated so that it doesn’t do what animal skin would otherwise do with the application of rainwater, perspiration and bacteria – turn into a stinking, rotting mess.

Nobody knows exactly when humans learned to tan leather, but the oldest fragment of tanned hide ever discovered comes from Armenia and dates from 3500 BC. That’s a pretty old shoe, but there’s evidence we’ve used leather even longer than that. By analysing stone flake tools, archeologists have found evidence that we were working with hides as long as 400,000 years ago.

The middle ages saw leather tanning come into its own with a boon in the industry that lead to the introduction of new products like suede and nubuck. Fast forward to the nineteenth century and a new production method revolutionised tanning, but polluted a lot of rivers.

Chrome tanning versus vegetable tanning

Tree tannins have been used to tan leather for thousands of years.
Image source: Anna Kepa

About 80% or more of the world’s leather is chrome tanned, a chemical process invented by German and Swedish inventors Friedrich Knapp and Hylten Cavalin in 1858. Finally patented by an American chemist called Augustus Schultz, chrome tanning produces superbly supple leathers that take a wide range of bold dyes.

But when it comes to shoes, the new ways aren’t necessarily the best. The best leather for shoes is vegetable tanned, a process that causes less pollution, exposes workers to less harmful chemicals and which creates the sort of leather that’s tough, durable and ages beautifully.

Plant leaves and tree bark contain substances called tannins which protect the living organism from attack by pests, fungus, and bacteria. When applied to animal skin, extracts from oak, chestnut or conifer bind to the proteins in the hide, reducing its susceptibility to decay.

The best leather for shoes

When you’re choosing a pair of new shoes, always go for vegetable tanned Italian leather, the best of which comes from Tuscany where small firms work together, each specialising in a different part of the tanning process.

Although Italian leather takes longer to process, and is more expensive to produce than its chrome-tanned equivalent, it’s well worth the wait. Vegetable tanning creates products that are naturally tougher, longer lasting and stunningly beautiful.

Vegetable tanning gives the leather a wonderful natural colour which can be dyed or simply left as it is. When you apply waxes or polishes to your vegetable tanned footwear, you change its appearance in a way that’s unique to your shoes – that wonderful patina of aged leather is the mark of vegetable tanning.

And don’t forget the smell – only vegetable tanned shoes have that wonderful aroma of new leather, a scent that comes from the woody perfume of the bark and leaf extracts used in the tanning process.

The environment

Unless carefully controlled, tanneries can flood local rivers with waste.
Image source: Avivalad

Tanning can be pretty rough on the rivers into which the waste effluent pours, and even natural vegetable tanning can, if not properly regulated, cause environmental damage. But chrome tanning, especially in developing countries like India, Bangladesh and China is highly toxic to the natural world and to the people employed in the industry.

Kanpur in India lies at the centre of world leather production, and is the industry’s biggest exporter. Most of the industrial effluent from the tanneries is dumped untreated into local rivers where it poisons crops, wildlife, and people. Thanks to world demand for cheap leather products, those living and working in the area suffer from asthma, blindness, skin diseases, cancers, and more.

By contrast, Italian leather made using the vegetable tanning process – like that used for Samuel Windsor leather shoes – is governed by strict EU regulations to ensure minimal environmental harm and maximum quality. Only after tanning is our leather shipped to India where we provide employment for expert craftsmen there.

Your feet

Shoes made from vegetable-tanned leather are comfortable and hard wearing.
Image: Clem Onojeghuo

While chrome tanned products are deemed safe for use by people, the chemical process does not end when the hides leave the factory. And while the danger is probably small, some manufacturers – like luxury car makers – will only use vegetable tanned leather because of the potential health risks posed by chrome tanned products.

That’s because chrome tanning uses Chromium III salts which are absorbed into the hide, protecting the protein in the leather from biodegradation. But when you expose Chromium III treated leather to heat – think car seats baked in the sun – some of this salt transforms into Chromium IV, and that’s highly toxic.

Vegetable tanned leather shoes are good shoes. Good for you, good for those who make the leather, and good for those who manufacture the shoes. Comfortable, hard wearing and practical, they’re good for your feet and, if they’re Samuel Windsor shoes, good for your pocket too.

Posted in Leather shoes.

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