Mike Redwood

Columnist

International Leather Maker


Sheep graze on the wide sandy coastal grasslands in a remote part of Wales amid a patchwork of ancient temperate rainforest. At the edge of the gnarled sessile oaks, quercus petraea, scrub and other small windblown trees, one oddly shaped specimen stands out as being different. It’s a black acacia, an Australian tree. It is here because of the tanning industry.

Sir Joseph Banks, the naturalist and botanist who took part in Captain Cook’s famous first voyage of discovery to the South Pacific, is credited with introducing it to the West. He later sent botanists to many parts of the world and helped make Kew Gardens in London arguably one of the top botanical gardens in the world. Many species were introduced to Europe through them.

He was also deeply interested in the uses of botanical materials in agriculture and industry. He was a strong supporter of instructing Sir Humphry Davy to look at the chemistry of tanning with oak bark – the major tanning method used in the UK in the late 1700s.

Davy built on the work of the French chemist Armand Seguin and isolated tannin, going beyond the concept of “astringency” that was being used to explain tanning. He showed how to identify and measure the tannin content, separating it from lignins and other materials he defined as non-tannins.

Natural tannins

He found that acacia types from India were high in natural vegetable tannins would tan faster than the long twelve months required for oak. He had it made and self-tested footwear to demonstrate its effectiveness compared to oak extracts. Later he showed that black acacia from Botany Bay in Australia was perhaps even better.

The tree was brought to Europe to be used for tannin and for the wood, which was good for paper. But it was also highly invasive, producing many seeds which were quickly spread widely by vermin, hence its arrival and survival in a remote corner of Wales.

It also was taken to South Africa, where it is now recorded as a weed, currently classed worldwide as one of the top 100 invasive species in the world. There, it started to be harvested on a rotational basis in carefully managed forests in various Southern Africa countries to form the basis of our current major mimosa supply. Trees are cut after about eight years and always replaced. The bark goes towards tannin and other materials, the wood for high quality specialist paper and the small branches for biomass in a highly sustainable system.

British tanners did not take it up with alacrity but did start to import tannins from around the world in untreated and extracted form so that, by the 20th century, a mix of chestnut, mimosa and quebracho had become more common, with oak long abandoned for mainstream production.

Between the lines

The work by Davy was outstanding. His method for analysing tannin stood as the standard for over 70 years, but his work was also remarkable for what it did not look at. It was well known that chestnut and other materials were used for sources of tannin throughout Europe with variations from North to South. Even the ancient Romans had brought their leather and the associated skills in tanning to the UK, and an Ottoman trader had presented in detail the method of vegetable tanning and dyeing only a few years before in London. He showed how brilliant yellow and red leather could be made from goat and sheep skins using the famous galls of the Quercus infectoria, the Aleppo oak, which was first mentioned as being a concentrated source of tannin by Pliny.

There are explanations for this inertia. Davy was keen to identify and isolate new elements such as potassium, sodium, calcium, strontium, barium and magnesium, along with chlorine and iodine. All while playing around with electricity and electrolysis; and looking at photography where he and the founder of photography, Tom Wedgwood, identified that white alum leather helped the image appear better than paper.

For tanners, oak-tanned bovine was the backbone for equestrian, everyday footwear and bag leather and all other leathers probably seemed irrelevant. The fact that Turkish leather, which later became tangled into the wider term of Moroccan leather in Northern European minds and has created confusion since, made beautiful lightweight footwear and an outstanding bookbinding leather did not appear relevant.

Looking for a faster horse

So, just as today with chromium, tanners were looking for a faster horse rather than the invention of the car. This is the very point that IULTCS Secretary Dr Luis Zugno has been frequently making when he discusses research and education in the leather industry, and in particular our ability to make truly competitive modern leathers.

While I recognise that the leather chemical industry continues to offer new materials, I remain convinced that too many of these new products are reacting to legislation in areas where a leather industry looking to move ahead would have eliminated the offending chemicals many years ago already.

Just like chromium, where we offer reasonable alternatives but have none yet that can properly work as well as wet-blue. These are subjects for the future, but it is quite right that the wider industry thinking needs to get away from the incremental and into entirely new territory.


mike@internationalleathermaker.com

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