Were steels mass-produced in Ancient India?

A high-steel carbon production technology from the southernmost part of the Indian Subcontinent may be one of the first examples in the world of a green industrial-scale process, as well as of automation.

    In the version of our history written by the colonial British, there is not much mention of Indian science and technology. After all, they wanted us to believe that, barring occasional flashes of brilliance, there was not much to write home about. Industry was strictly cottage-scale, not supported by a systematic knowledge-creation tradition. The Indians were lazy, and wasteful, content to produce things on tiny scales, using skills that did not go beyond tinkering. Their only advantage was the fact that their land was blessed with spices, which they were able to sell at exorbitant prices to eager European markets. The uncharitable, even patronising, remarks of early 19th century surveyors like Francis Buchanan when describing the Indians’ metallurgical practices are hard to miss.

However, this picture is at odds with the high esteem in which Indian steels were held throughout Western Asia and Europe throughout the Medieval and Early Modern Periods. Also, it is difficult to imagine that unorganised cottage metal works were able to keep up supplies of such high quality metal for such a long period of time. Many accounts also suggest the Indians were exporting vast amounts of ingots for making the fabled Damascene or Wootz steel to Persia and further afield. Further, readers may be surprised to note that brass, so commonplace in India from time immemorial, was practically unknown in Europe: it was only in 1781 that Europeans were able to make brass for the first time by alloying copper and zinc. Then, there was the corrosion-resistant iron that was being used extensively in India.

The downplaying by the British notwithstanding, India’s ancient steels have been the subject of much research in the West since the colonialists sent samples to Michael Faraday to try and reverse engineer them, an attempt that itself ended in failure but gave rise to the discipline of metallurgy. More recently, a University College of London archaeologist, Gill Juleff brought out another interesting facet of the Indian Subcontinent’s ferrous metallurgy.

In Sri Lanka, Prof. Juleff made the intriguing discovery of iron smelting sites, always on the western or windward side of mountains and ridges, which faced the monsoon winds. As if this was not baffling enough, she discovered rectangular blocks of slag, rather than circular ones that one would expect to form in traditional round furnaces (slag is the byproduct of metal production from ore). There was only one way to figure out how steel was being produced at such locations: by recreating the technology. She set about doing precisely this, and as she went about it, learnt many fascinating things about the process.

The horizontal C-shaped furnaces were built into the mountain walls, and oriented north-south. A flat wall brought up the front of the furnace. The base of the furnace was slightly hollow and the front of the hollow along the flat wall was lined with tuyeres, or clay tapering pipes, telescoping into each other. Tuyeres were also built into the front wall, and evidently, they were meant to let in air to enable the smelting process happening inside the furnace. The furnace itself was packed with the feed - crushed ore, charcoal and flux, mixed in the right proportions - and the smelting process started by igniting the charcoal.

A reconstruction by Prof. Gill Juleff of a furnace that was used for producing the subcontinent’s famed high-carbon steel in the mountains of Sri Lanka. (Courtesy: website of Wilpattu House homestays)

Here’s the astounding fact: once the charge has been ignited, the operation requires no further human intervention. Draughts of the monsoon wind, entering the furnace through the tuyeres, would heat the charge up to the requisite temperature. In the traditional bloomery furnace, manually-operated bellows were required for blowing air into the furnace to heat up the charge. The slag produced by the operation would flow through the tuyeres lining the front edge of the floor of the furnace, and eventually down the mountain slope, with no need for manual tapping and removal. The tuyeres were embedded in the front wall at the right angles to prevent gusting, which would then prevent the wind from flowing smoothly into the furnace. The slag that remained at the bottom was what Dr. Juleff had observed as the nearly-rectangular blocks mentioned above. At the end of the operation, high-carbon steel could be recovered from the furnace.

The use of charcoal and seasonal monsoon winds makes this a very “green”, or environment friendly, process. The process may also be the earliest instance of automation for producing a large-volume product, if we ignore the (negligible) manual intervention required in charging and emptying the furnace. The furnaces could be reused. To increase the scale of production, all that was required was a longer furnace, keeping all other dimensions and feed proportions the same. What more can one ask for?

Dr. Juleff’s reconstruction of this ancient process explains how “Sarandibi steels” came to be highly regarded for swordmaking in Arabic accounts in the Mediaeval Period (Serendib is the old Arabic name for Sri Lanka). It was by using such furnaces, that were so easy to scale up, that the southern part of the Subcontinent was able to sustain high levels of production of excellent high-carbon steels like the Wootz or Damascene that were exported in large quantities for many centuries. Juleff also points out that this process eventually spread to Southeast Asia along with Buddhist influence, and thence, to Japan, where it inspired the design of the long, rectangular furnaces for producing the famed Tatara steel that was used for making Samurai swords.

This stunning high-carbon steel production technology could not have been perfected without many years of experimentation. This technology clearly illustrates that ancient Indians were keen observers and outstanding innovators, who were quick to harness any resource or phenomenon to their end, provided the outcome was not deleterious to the environment. The Indian metallurgical tradition was one of continuous innovation and refinement that had no equal in the world, and was the result of systematic enquiry and sustained multi-generational knowledge-creation, which went on to inspire similar traditions in large parts of Asia.

• 46 min read
• 2
• 0