The ancient art of leather production
The ability to make leather has a long and rich history that stretches over the millennia.
Image © Victorian Picture Library
Who first invented – or discovered – the leather making process? Several cultures have been credited with initially identifying how to tan animal skin, including the inhabitants of Mehrgarh in modern-day Pakistan, the Sumerians (in what is now southern Iraq), the Egyptians and the Hebrews. Whatever the answer to this age-old question, it is evident that when our ancestors decided to wrap pieces of softened animal skin around their feet to protect them from stones and thorns, they were able to walk faster and more safely. Similarly, animal skin clothing could protect their bodies from the elements and food could be conveniently carried in bags manufactured from this readily-available material. When peoples who formerly lived as nomads established agricultural settlements, the birth of animal husbandry provided a steady and accessible source of both food and skins.
However, untreated skins (and the products made from them) could become hard and brittle or rot away, so they were of limited use. Undoubtedly then, identifying a way to make a skin flexible and long-lasting was a major step forward in human development. One suggestion for how leather was first made is that tanning was discovered accidentally – perhaps when animal skins that had been lying in pools full of rotting leaves and bark from oak trees no longer putrefied. Once the skin was in this stable state, it could be softened by rubbing in fats and oils.
Museum of London
Different tannins were found to be effective. For example, the ancient Egyptians and Mesopotamians reportedly used the bark of the gum arabic tree – Acacia nilotica – and other methods of tanning were based on the use of sesame oil. Some historians suggest that a number of leather types, including a supple alum leather called ‘aluta’ and durable leather for sandals were being manufactured in the city of Rome soon after its founding in the 8th century BCE.
With experience came sophistication. Leather makers soon realised that scraping away excess flesh and fat could improve the product. It was then discovered that using a solution of water and the ash from a fire enabled easier removal of hair from the skin – a process now known as ‘liming’. As the demand for leather grew, dedicated tanneries large and small were set up in one place after another.
The English word for tanning is believed to have its root in the medieval Latin tannare, which itself is a derivative of tannum (oak bark). Other languages commonly spoken in Britain’s earlier history display a similar commonality, such as the French tan (tanbark) and the old Cornish tann (red oak).
A tough occupation
To say that the work of an ancient tanner was unglamorous would be an understatement. The preparatory stage was arduous and could take several weeks. Skins arriving at the tannery were typically stiff and dirty with dried gore, so the tanners would soak them in water until they were clean and soft. Any remaining flesh and fat would then be removed by pounding and scouring the skin. Hair was loosened by painting the skin with the previously-mentioned alkaline lime mixture, soaking it in urine, or simply allowing the skin to putrefy for several months. After that, it could be dipped in a salt solution and then the tanner would scrape off the hair with a knife.
The next step involved the tanner ‘puering’ (softening) the skin by soaking it in a solution of animal brains or by pounding in dung – commonly from dogs or pigeons – until the skin became supple. This was a fermentation process that relied on enzymes produced by the bacteria found in the dung. The tanner of ancient times often used his bare feet to knead the skins in the dung water – a process that could take two or three hours.
It is interesting to note that, while the vast majority of tanneries today are mechanised, with many using full of state-of-the-art computerised equipment, there are examples of leather makers popular with tourists using ancient methods – such as those in Fez, Morocco. For example, skins are first soaked for two or three days in a mixture of cow urine, quicklime, water and salt – a caustic mixture that helps to loosen excess fat, flesh and hair. The tanners then scrape away excess hair and fat to prepare the skins for dyeing. In the next step, the skins are softened in a mixture of water and pigeon dung after which they can absorb dye easily. Just as in the past, the tanner uses his bare feet to knead the hides to achieve the desired softness. All this preparatory work would be done prior to traditional vegetable tanning.
Kept outside the town
It was the combination of animal dung, decaying flesh and urine that made ancient tanneries so repulsive. Tanning was considered a ‘noxious’ or ‘odiferous’ trade, and as a result it was forced to locate to the outskirts of the town. Nothing has changed – where the production of leather by these ancient methods is even now carried out, it is normally considered to be so foul-smelling that such tanneries are still isolated from nearby towns. Interestingly, the Bible book of Acts records that the Apostle Peter spent ‘quite a few days in Joppa with a certain Simon, a tanner, whose house was by the sea.’ The work of a leather maker was considered unclean and demeaning from a Jewish perspective, with tanners being placed on a social level below dung collectors. Simon’s work brought him into regular contact with the dead bodies of animals, meaning that he would be in a constant state of ‘ceremonial impurity’. According to a number of different sources on the subject, Simon may well have used seawater in his tanning, and his workshop was likely located on the outskirts of the town because of the smell.
Children employed as dung gatherers were often seen in ancient cities. Also common were pots located on street corners, where human urine could be collected for use in tanneries or for cleaning laundry.
Different tanning processes
While the use of urine and animal brains appears to be quite universal with ancient tanners around the world, some unusual – perhaps even unique – practices could be found. For example, people living in colder climates, such as what is now called Greenland or Alaska, would scrape the hides (typically seal skins) with curved ulu knives or special stone scrapers to remove the hair. The hides would then be beaten and softened with urine. In the next stage the leather workers, who were mainly women, would bite the hides until they became very soft and then rub them with fish oil and fat.
A different method of tanning was reconstructed from leather garments dating from the fifth century BCE that were discovered preserved in Greenlandic ice. At the outset, the hide’s layer of fat was apparently removed with clay, after which it was covered with a mixture of animal brain, fat, liver and salt. In the next part of the process, the hides were sewn together with needles made from bone or horn to create a round tent, and phenol – an active tanning ingredient – was introduced in the form of smoke from an open fire.
From ancient times leather makers have used tannin derived from tree bark and certain plant leaves. In some variations of the process, alum or cedar oil were applied to the skin as a tanning agent and, as the skin was stretched, it would absorb the agent.
Leftover leather could be used to make adhesive. Scraps of hides would be placed in a vat of water and left to deteriorate for several months. The mixture would then be boiled to produce what was called ‘hide glue’.
Wide variety of uses
Ancient civilisations found many applications for leather, including armour, bags, boats, boots and sandals, harnesses and tack, quivers, scabbards and water skins. Leather panels were also affixed by copper studs to chariot wheels.
European leathergoods manufactured during the Middle Ages (generally accepted as between the 5th and 15th centuries CE) included belts, bottles, bridles, buckets, chairs, ink wells, satchels, shoes and even coins.
As their experience increased, European tanners and leather workers established trade guilds in order to maintain control of the supply of this much sought-after material. Elsewhere, Arab craftsmen improved the art of tanning, which led to ‘Morocco’ and ‘Cordovan’ leathers becoming highly-prized in Western Europe. Particularly from the late 16th century, Morocco leather was valued as the material of choice in luxury book bindings due to its strength and its ability to hold gilding well.
Colour, decoration and new chemicals
For thousands of years, humans have adorned themselves with leather that has been decorated by such methods as gilding, painting, stamping and tooling, and which has often also been coloured with a plant-based dye. During the 14th and 15th centuries, ornamentation in leather was often produced by cutting a drawing into the grain side which was then emphasised by beating it from the fleshy side.
Traditional dyeing is still practiced in the Moroccan cities of Fez and Marrakesh, where all the colouring agents are reportedly natural and plant-based. Bright red dye is obtained from bell pepper or poppy, rose is used for pink, orange colouring comes from henna (which can be mixed with sugar to achieve a black dye), indigo provides blue, green is obtained from mint, and pomegranate with saffron create yellow dyes.
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The Industrial Revolution – which began in Britain in the mid-18th century – brought rapid advancement in both chemistry and technology, and this helped to increase efficiency and diversity within the leather making industry. Patent leather, known for its glossy surface, was invented towards the end of the 1790s (see the article ‘The birth of patent leather’ for a detailed consideration of this material’s development).
Around 1840, the medical fraternity adopted the practice of soaking gut sutures in a chromium (III) solution. It was then discovered that chromium salts could also be used in tanning and so was embraced by leather makers. Chrome tanning streamlined the manufacturing process and eliminated many of the preparatory steps required for traditional vegetable tanning. It has been estimated that some 80-90 per cent of tanning worldwide today employs chromium salts.
The technological changes brought about by the Industrial Revolution saw a gradual mechanising of leather making. The mid-19th century saw the introduction of powered equipment that performed such operations as splitting, fleshing and dehairing, but that is an entirely different story.
Into the 21st century
The process of leather making – a skill that was perhaps discovered by chance – has proved to be one of the most valuable lessons in the development of the human race. The material has certainly been very versatile and, although synthetic alternatives and pressures from some sectors of society have affected the use of leather as a basis for many products, it still enjoys significant popularity with consumers around the world.
How can we help?
Please contact SATRA’s footwear team (firstname.lastname@example.org) for the testing of leather products and components, or email email@example.com for assistance with checking leather for the presence of restricted substances.
This article was originally published on page 30 of the October 2020 issue of SATRA Bulletin.