May 20, 2025

Going faster, getting poorer

We have bemoaned the fact that the leather industry was slow to industrialise for a long time and continued with ancient processes until uncovering the wonders of modern science with chrome tanning at the end of the 19th century.

By about 1200 BCE, the main tanning processes were being used and for the next 3,000 years little happened. Oil tanning uncovered more oxidisable oils and learned to make chamois, while alum was tested with egg yolk and flour to make a neat glove leather.

By the 18th century, the U.S. was uncovering the foundations of mass production with interchangeable parts that did not require the skills of an artisan at every turn. With a shortage of people and craftsmen, it was not surprising that they started to mechanise the labour-intensive tannery processes. Bark mills to chop the bark into small pieces, and then sammying and shaving devices came along, among others that could be driven by water and belting, before steam simplified things.

It was also the period when the Scientific Method evolved out of philosophy: chemistry became a science akin to today’s thinking. Careful measurements showed that burning was not caused by the liberation of phlogiston but rather by a process of oxidation. Empirical observation and experimentation, distinct from purely philosophical reasoning, took over and chemists such as Armand Séguin, Humphry Davy and Joseph Proust changed thinking about leather.

Introduction of chrome tanning

We argue the first real change only came after chrome tanning was tortuously made a success from 1850 by Cavalin, through Knapp and Augustus Schultz’s two-bath method in 1884. But sadly, consumers were already noticing the difference in industrialised leather making, faster processes and new vegetable tannins and acid. The introduction of stronger acids and new sources of tannin from all round the world created big casualties. First was the bookbinding industry with complaints about book covers disintegrating, with particles of powder falling off with every handling.

This was a consequence of acid hydrolysis. It has never been fully understood but was clearly caused by what became termed “industrial” vegetable tanning where large factories used stronger acids, extracts from condensed tannins such as quebracho, gambier and mimosa to make their leathers faster and a little cheaper. High humidity and temperature, plus urban air pollution, in the libraries served to accelerate the degradation.

With time the problem only got worse. It was found also in furniture and elsewhere. The fact that red rot is irreversible at the structural collagen level meant only consolidation or replacement works, and the consolidates are far from perfect, with many better ones now withdrawn on health grounds. Left untouched, affected leather continues to deteriorate and is creating a nightmare with collections of 19th century record books being continuously unearthed and requiring urgent treatment. Two big markets were hugely damaged and have never fully recovered.

With the excitement of Schultz and mineral leathers, quickly followed by Dennis’s easier-to-use single-bath chrome tanning process sold as Tanolin and free from royalties, this totally revolutionised the leather industry. Pits became drums, months became hours, retanning was everywhere and finishing a major process. Alongside all this came another innovation that the customers had not asked for: mass production of side leather.

With chrome tanning predominating, every hide from veal skins upward going that route was cut down the backbone. As the leather industry advanced, sides became standard to meet the needs of large-scale manufacturers and to optimise shipping and storage.

Tanners know perfectly well that the central part of the hide offers the most consistent thickness and quality, which is ideal for high-volume, standardised products. Bellies will be thin and stretchy while shoulders tend to be thicker with more irregularities, such as deep neck wrinkles, making them less desirable for many mass-market applications. Which is exactly why the previous approach often cut off the bellies to be tanned differently for light leather goods and the like, and shoulders for shrunken grain or use in sandals where smaller pattern pieces can avoid defects. Hides are left whole for upholstery and other uses requiring the full area.

Sides have neck, belly and back, which makes it hard to achieve a level aniline cover, a smooth grain and a consistent handle. To meet the requirements of the most demanding market, increasingly wanting to mechanise and deskill shoemaking, demands were made that leather should be not just an engineered product with tight specifications but as close to plastic as possible. As with movable parts, skills of hand and eye are replaced by mass mechanisation.

The automobile industry had more justification to follow the same route as the in-use demands on leather – with drivers wearing jeans with zips that catch the seat edges and enjoy dumping bricks on the rear seats. Yet designers wanting softer and more natural leathers were outvoted by production engineers demanding 100% level colouring. Automotive leather quickly drifted towards plastic.

With so much leather commoditised, it has been a small step for clients to shift to their confusingly named petro-fibre alternates. Simon Neifer of Pulcra Chemicals wrote on social media: “We took one of the most soulful, natural, and character-rich materials the world has to offer, and taught ourselves to fear it.” I agree but would argue we largely did it to ourselves.

From the moment Humphry Davy let us free to introduce gambier, mangrove and tans from Botany Bay, it has been shown to have been careless and reduced quality at the expense of financial “efficiency”. “Time and tanning makes great leather,” we said and then removed the time and the craft from the art of tanning and handed it to the machine.

A topic that we all need to spend further time contemplating.

Michael Redwood

Leather chemist, writer, and advisor on responsible leather manufacturing and material strategy. This article was originally written for ILM.