Anil Kumar Suri
What Metallurgy Can Tell Us About Our History

An exploration of metallurgy in India.

The history of metallurgy in India can tell us a lot about the history of India itself. Our scientific heritage has inexplicably always been given short shrift in our history textbooks, as pointed out here and here. It is, therefore, not very surprising that our historians don’t enter at all into this rather technical, if extremely fascinating, aspect of our history.

The use of metals marks major epochs in the history of any culture. The Bronze Age in India began around 3000 BCE in the Indus Valley region. The ancient cities of the Indus Valley Civilization (2600-1900 BCE) were part of India’s Bronze Age. The Indus Valley Civilization, also called the Mature Harappan phase, is merely the most well-known period of the Indus Valley Tradition (7500-300 BCE), which began with Neolithic (i.e., New Stone Age) settlements, such as in Birrana, Haryana (c. 7500 BCE) and Mehrgarh in Baluchistan, Pakistan (c. 6750 BCE). Another group of Bronze Age nomadic tribes, the Indo-Aryans, were believed to have entered the subcontinent in the second millennium BCE, contributing, in some versions, to the decline of these cities; the Indo-Aryans settled down in what is today Punjab and Haryana (where they composed the Ṛg Veda), slowly moving eastward and eventually founding their own cities on the Gangetic plains, in what is known as the Gangetic Tradition. These Indo-Aryans were also supposed to have begun India’s Iron Age around 1000 BCE.

Although archaeologists now overwhelmingly agree there is no evidence of such an invasion or migration, and inspite of it being based almost exclusively on unverified philological arguments, the supposed advent of Indo-Aryans continues to be the norm in academic discourse, is what is taught in textbooks, and guides prevailing constructs of ancient Indian history, such as a supposed culture shift that I had tried to examine earlier. Here, I try to look at India’s history from a more technological perspective. The picture that emerges shall not only leave us much better informed about India’s ancient history, but may undo our current simplistic notions of Stone, Bronze and Iron Ages.

The implications for the dating of the Vedas and other ancient texts

Estimates for the dates of the composition of the Ṛg Veda vary from 1900 to 1200 BCE. The term, ayas, occurring in the Ṛg Veda has been interpreted as copper. Scholars also believe that the term, kṛṣṇa ayas, which occurs in the Yajur and Atharva Vedas, but not the Ṛg, means iron, and implies that the Yajus and Atharva belong to the Iron Age, and hence were composed after 1000 BCE. The events described in the Mahābhārata too are ascribed to the Iron Age. Thus, when, how and where metals like copper and iron came to be used on the subcontinent could inform our understanding of ancient India.  

The bronze technology of the Harappans

Copper ore was abundantly available to the Harappans from the Aravalli ranges and the Chagai region of Baluchistan. Copper, however, is a difficult metal to smelt. Alloying even a small amount of tin with copper makes for a melt that is more fluid, and significantly reduces air entrapment; thus, the casting process becomes much easier, and the products are of higher quality. The resulting bronze is stronger and harder than either metal. Early on, ancient people alloyed copper with phosphorus or arsenic (whose fumes are toxic), but realised that tin was far more advantageous, and tin-bronzes incomparably superior. The use of tin to make bronzes was a major technological advancement. Today, we tend to use the term bronze only for an alloy of copper and tin.

Like other ancient cultures, the Harappans too switched to tin-bronzes in the second half of the third millennium BCE. The tin content in Harappan bronzes varied from 1-2 per cent to as high as 8-12 per cent. A higher tin content results in greater hardness. Interestingly, objects which required hardness, like knives and axes, had high proportions of tin, whereas common objects for which hardness was not particularly required had lower amounts of tin. This implies that the tin contents in the bronzes may have been varied purposely according to function by the Harappan metal-workers.

Tin contents above about 11 per cent raise a further exciting possibility. Such bronzes are what are technically called “polyphase”. The properties of a polyphase alloy can be manipulated by heat-treatment to obtain a desired combination of strength and hardness. Indeed, the fact that objects like knives and axes – which need excellent mechanical properties – have been found to have as much as 12 per cent of tin raises the question if the Indus Valley smiths had mastered this technology too. To throw more light on such questions, a detailed technical analysis of the Harappan bronzes is called for. In later centuries, the Indians would develop remarkable steel technology, best exemplified by the (wrongly-named) Damascene swords, which combined toughness with sharp edges, made by carefully engineering the iron-carbon phases. It would be no surprise if it emerged that this steel technology was the natural progression of metallurgical knowledge developed during the Indus Valley Civilization period.

The dog in the night-time: the curious case of tin 

With the decline of the Indus Valley Civilization, the use of tin stops too. Tin does not occur in the copper-base articles found in the subsequent Copper Hoard cultures, or in the Painted Grey Ware sites. Both these post-Harappan cultures have for long been associated with the incoming Indo-Aryans. However, there is a slight problem. As one of the greatest authorities on the Indus Valley Tradition, J. M. Kenoyer asks, 

“…the northwestern regions were the source of the movements of the so-called Indo Aryan speaking people. Yet, if there were such movements, why did the migrants not supply one of the most important raw materials for bronze production, i.e. tin? … Such a long break in tin acquisition is important because it would reflect the lack of contact with the regions of Baluchistan and Northern Afghanistan…”

[Kenoyer Jonathan, M. (1995). 10. Interaction systems, specialised crafts and culture change: The Indus Valley Tradition and the Indo-Gangetic Tradition in South Asia. In G. Erdosy (ed.), The Indo-Aryans of Ancient South Asia: Language, Material Culture and Ethnicity, p. 213-257. Berlin, de Gruyter.]

This presents a huge problem whether one is talking of an Aryan Invasion or a Migration. These two regions are from where the Indo-Aryans are supposed to have entered the subcontinent. Both have deposits of cassiterite (an ore of tin) and Afghanistan is close to the tin mines of Central Asia, which may have supplied the various ancient Bronze Age cultures of the region. The Harappans are believed to have established the remote Shortugai on the banks of the Amu Darya in Afghanistan, as an outpost specifically to facilitate trade with mineral-rich Afghanistan and Central Asia. Significantly, the use of copper ore from the Aravallis itself continued seamlessly into the Gangetic Tradition.

For decades, scholars attributed the introduction of the horse to the subcontinent to the incoming Indo-Aryans. Archaeologists today regard this argument as simplistic and unnecessary; indeed, there is strong evidence for the presence of the horse on the subcontinent from much before the supposed arrival of the Indo-Aryans, as detailed by Danino. However, if the introduction of the horse could at all be regarded as evidence of an Indo-Aryan migration, is it not very strange that these very people should not also bring with themselves an obviously valuable resource, that too in an era of thriving trade all over the region? Another leading Indologist, Edwin Bryant, sums it up:

“The Vedas, after all, speak of and value bronze as well as the horse. The argument here is why did the bronze-using Indo-Aryan speakers not convey tin into the subcontinent from the northwest if they were arriving from those areas?”

[Bryant, E. (2003). The Quest for the Origins of Vedic Culture: The Indo-Aryan Migration Debate, p. 224-237. New York, Oxford University Press.]

To this, one may add the fact that the Yajur Veda expressly mentions tin as prized – the Camakam following the Śatarudrīya in the Taittiriya Samhita of the Kṛṣṇa Yajur Veda recited daily by many Indians reads, Trapuṣcame (May we be blessed with tin, trapu). Tin is also mentioned in the Atharva Veda. Clearly, the Vedic people knew the value of tin.

Was the Harappans’ bronze technology indigenous?

Did the Harappans learn bronze-making from other Bronze Age Central Asian cultures, and obtain their tin from there? The greater likelihood is that they discovered the naturally occurring tin ore near the copper deposits of the Chagai district of Baluchistan itself that were already familiar to them. As tin melts at a very low temperature (232 °C), it may have been accidentally discovered by potters.

This may also explain why the use of tin declines after the Mature Harappan phase. Once their culture went into decline in the Sarasvati-Indus valley owing to climatological reasons, and the locus of activity shifted slowly eastward towards the Gangetic plain, contact with Baluchistan tapered off. Copper, however, continued to be available from the Aravallis. It was probably the non-availability of tin and the consequent difficulty in making bronze that, at least partly, triggered an increasing reliance on iron.

The appearance of iron

Many communities have traditionally smelted iron for a living in India. They do not rely on reaching the melting point of iron to separate it from the slag (the material left behind from the ore after the metal has been collected). Instead, they use a combination of naturally occurring materials like charcoal, and minerals like limestone as “fluxes” to smelt the metal at relatively low temperatures. Indeed, in many early first millennium BCE Chalcolithic (Copper Age) sites in India, archaeologists have found that iron smelting was done in low-temperature furnaces basically designed for copper. So how long ago did Copper / Bronze Age people succeed in smelting iron? 

Secondly, it is always assumed that the Iron Age follows the Copper / Bronze Age, as the ability to reach the melting temperature of copper (1085 °C) would have been attained before that of iron (1538 °C). But if iron can be smelted at low temperatures, was it even necessary for people to have learnt the art of copper smelting before discovering iron? After all, copper too must have been a chance discovery, and in many places in India, iron ore is easily and abundantly available on the surface itself without the need for mining.

Discovery of iron by Stone Age cultures

It turns out that Megalithic (Stone Age) cultures in peninsular India were producing iron too, that too from as early as the first half of the second millennium BCE. [Possehl, G. L. and Gullapalli, P. (1999). 6. The Early Iron Age in South Asia. In V. C. Pigott (ed.), The Archaeometallurgy of the Asian Old World, p. 153-176. Philadelphia, University of Pennsylvania Museum.] The earliest dates for iron smelting have been moving steadily backward with new discoveries, from Naikund, Maharashtra (800-700 BCE), Komaranahalli (c. 1400 BCE) and Hallur (c. 1500 BCE) Karnataka, Veerapuram and Ramapuram in Andhra Pradesh (c. 1500 BCE), and Paiyampalli, Tamil Nadu (1900 BCE). Thus, we find Praveena Gullapalli saying,

“Apparently the development of a full bronze technology … is not a necessary precursor to the successful development of an iron technology. … In fact, the term Metal Age might be a better descriptor of what appears in South India.”

[Gullapalli, P. (2013). 14. Lamination as Production Technique: Patterns and Possibilities. In S. A. Abraham, P. Gullapalli, T. P. Raczek and U. Z. Rizvi (eds.), Connections and Complexity: New Approaches to the Archaeology of South Asia, p. 263-278. Walnut Creek, Left Coast Press.]

But what of the Gangetic plain, where the Indo-Aryans were supposed to have been expanding? South-eastern Uttar Pradesh is of enormous historical significance. It encompasses the regions identified with the legendary kingdoms of the Sūryavaṃśa (Kosala on the Sarayupar plain), and the earliest Caṃdravaṃśa (with its capital in Pratiṣṭhāna, now Jhusi near Allahabad). In this region, furnaces for iron smelting, slag and iron objects dated to 1800 BCE have been found, as have copper objects dating to 2700 BCE – i.e., contemporaneous with the Indus Valley Civilization. In fact, the village of Malhar (Chandauli district) seems to have been a major ancient iron-producing site. Further, archaeologists have found Neolithic settlements in this region dating to c. 7100 BCE, i.e., as old as those of the Indus Valley Tradition (see second paragraph). Rice was cultivated here from the seventh millennium BCE, as were some winter crops like barley and wheat, which were more typical of the Indus Valley Tradition, indicating close interactions between the two regions from Neolithic times.

How advanced was iron technology in the first millennium BCE?

I should re-word my question: how advanced was steel technology in the first millennium BCE? Not only was iron production well-established by this time, a remarkable level of mastery of the alloying iron with carbon appears to have been achieved. Objects like daggers and sickles discovered in Bengal and dated to around 900 BCE have been revealed by analysis to be polyphase – they contain phases technically called ferrite and pearlite, obtained purposely by slow cooling (Possehl and Gullapalli, ibid.). Further, these implements had lower carbon content in their interior (~0.5%) compared with their exterior (~0.8%), indicating that they were deliberately engineered to have the best of both worlds: a strong core and a hard surface. The relationship between the composition, and hence “microstructure” of the steel and its properties, and the control of the microstructure during processing to obtain a desired set of properties is the crux of steel technology. Such an advanced level of steelmaking was not achieved in the west till more than three thousand years later.

So did the ancient Indians indeed transfer their knowledge of alloying acquired whilst working with bronze, to steel-making? The probability is very high. In both cases, they appear to show deep knowledge of, and skill in, heat-treatment and microstructural control. This would also imply that there was a strong continuity of indigenous metallurgical knowledge and skills from at least around 3000 BCE to 900 BCE and beyond. 

Let us now turn to the Indus Valley Tradition itself.

Bronze Age iron in the Indus Valley?

Manda in Jammu is the northernmost known site of the Indus Valley Civilization. About 150 km to the north-east of Manda as the crow flies is the Megalithic site of Gufkral in Kashmir. Excavations in Gufkral revealed iron objects dating back to c. 2000 BCE. Thus, the advent of iron technology here overlaps with the Mature Harappan phase (2600-1900 BCE).

Iron objects have been found in as many as eight Indus Civilization cities, as distant as Mundigak in Afghanistan, and Lothal (Gujarat) in India, which were dated to the second half of the third millennium BCE. These objects have not been analysed and, so there is no certainty if they were smelted. However, it is worth noting that iron ores were used as fluxes in the smelting of copper in ancient times, and other ancient Bronze Age cultures too seem to have smelted iron accidentally while trying to smelt copper. Thus, iron may indeed have been smelted by the Bronze Age Indus Valley people. An object found in Lothal had the unusual composition of about 90% iron and 10% copper, suggesting smelting from a mixture of iron and copper ores. Sometimes, lumps of what appear to be iron ores like magnetite were used as such; further analysis of these objects is required to tell if these were cases of improper smelting. In Ahar near Udaipur in Rajasthan, several iron objects as well as iron slag datable to about 2000 BCE were found. Thus, it is reasonable to believe that the smelting of iron was known to the people of the Indus Valley Civilization.

Scholars are now seriously debating what might be reasonably accurate definitions of Stone, Bronze and Iron Ages, and when exactly these periods can be taken to have started. That, however, is merely a question of semantics. The crucial point is that the archaeometallurgical evidence of the last two decades calls for a fundamental revision of current theories of the entry of a foreign people into the subcontinent in the second millennium BCE, and the subsequent start of iron technology in India by these immigrants from around 1000 BCE. Currently accepted dates for the composition of the Vedas and Epics may also need revisiting.

A cottage industry?

In their usual attempts to downplay the technological achievements of the Indians, European historians and chroniclers often characterised Indian iron- and steel-making as a cottage industry, and an inefficient and wasteful one at that. This description, of course, misses a small point: would so inventive a people not explore possibilities to make production easier and cost-effective by mechanisation and scaling up?

In a report in the scientific journal, Nature in 1996, Gill Juleff brilliantly reconstructed an ancient iron smelting process employed in Sri Lanka, which ingeniously used wind to create draughts adequate to smelt iron in furnaces. Furnaces, some of which dated back to the third century BCE, were built into the slopes of the mountains on the southwest coast of Sri Lanka, and the wind blowing against the slopes was channelled into these furnaces through tuyères. (Before this discovery, it was believed that the use of bellows to blow air in through tuyères, thereby forcing draughts through the furnace was as good as it could get.) This principle was used to operate scores of furnaces, sustaining an annual production of several tons of steel – an astoundingly high output for that era – in that region alone. Scholars believe similar technologies could have been used all over South India, and were probably responsible for elevating it to its widely-attested world-leading position in high-quality steel production till medieval times. Dr. Juleff’s discovery is described in popular science articles here and here. Indeed, this may be among the world’s first examples of mechanisation – to the extent of minimising the involvement of humans – and industrial scale-up of a manufacturing process.