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Minerals and Metals in Ancient India v1.c20.s1: The Science of the Ancient Iron Technology

Minerals and Metals in Ancient India v1.c20.s1

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The Science of the Ancient Iron Technology

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Different metallurgical traditions were possible on account of easy availability of the ores and the ease in thier reducibility to the respective metals having not too high melting points. Table 12.1 provides the melting and smelting temperatures of some metals of archaeological importance.

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It is evident that tin and lead ores were the easiest to smelt. In a furnace providing a temperature of 1100-1200°C all the five metals except iron, mentioned in the table, could be easily smelted and the molten metals could be alloyed and cast into various shapes.

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At a temperature of 1200°C, iron oxide could be reduced to the metallic and solid state (not molten), provided the partial pressure of oxygen was low and CO/CO₂ ratio in the carbothermic environment high. There are archaeological finds of ‘magnetic copper’ and evidences of accidental production of iron in the copper smelting of sulphide ores. (Ashenbrenner and Cooke, 1975) It is further claimed that copper slags containing iron oxide phases might have been smelted to produce iron. However, it should be noted that iron silicate phases in copper

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Table 12. 1

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Melting and Smelting Temperatures of Some Metals of Archaeological Importance

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| Metal | Melting Point in °C | Minium Reductivce Smelting Temperature in °C |
| Tin | 232 | 600 |
| Lead | 327 | 800 |
| Silver | 960 | 800 |
| Gold | 1063 | 1063 |
| Copper | 1083 | 400 |
| Iron | 1540 | 800 |

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slag are not easily reducible to the metallic state, and the hypothesis of discovery of iron in a chalcolithic smelter may not be universally true.

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Man-made iron can be easily distinguished from meteoritic iron which almost always contains high (more than four) percentage of nickel. In the ancient Near East and eastern Mediterranean, iron ore used to be smelted in small furnaces resembling copper smelting furnaces. (Tylecote, 1962; Maddin et al., 1977; Maddin, 1982). Furnaces about a meter deep and about two-thirds of a meter in diameter were filled with iron ore and charcoal in a number of layers. A clay tuyere was led in from the side or from the top and attached to a bellow. The temperature in the hottest part was around 1200°C, and although reduction took place due to low Po₂ and high CO/CO₂ ratio, the metallic product was not liquid but a spongy mass.

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Caught up in the spongy solid mass was slag, mostly fusible ferrous silicate or fayalite (melts at 1170°C). The slag had to be squeezed out of the sponge iron by hammering at or above the temperature (1170°C) — a process known as forging. Hammering produced a continuous network of iron grains, sometimes interrupted by stringers of remaining slag elongated in the direction of the deformation of the iron bloom.

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Unlike copper, iron objects had to be forged stage by stage from a spongy mass or bloom to a bar, then thinning, pointing, folding and largely forge-welding at white heat. This knowledge did not come to the copper-smiths automatically, and thus it took centuries of a chalcolithic age to obtain the first few pieces of forge-welded iron.

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Even at this stage, iron was hardly useful because wrought iron, containing very little carbon, is softer than ten per cent tin bronze which was well-known to the copper-smiths. Despite the early successes to make iron (Coghlan, 1956) in Anatolia, Mesopotamia; Egypt and Afghanistan (3000-2000 BC), also later in Crete, Cyprus (2000-1600 BC) and still later in Greece and the islands of the Eastern Mediterranean, (1600-1200 BC), the spurt and diffusion of iron technology did not take place till 1200 BC, when it became known that iron can be carburized and hardened. The discovery must have been accidental.

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The solubility of carbon in iron is small at room temperature, but it increases greatly above 910°C. The hot spongy mass of iron when kept in prolonged contact with charcoal, absorbed carbon into the surface layers and thus became surface-hardened. The iron with the absorbed carbon is arranged in a two-phase structure called pearlite, which consists of alternate layers of soft and ductile iron (ferrite) and hard and brittle iron carbide (cementite). The hardness of the carburized sample depends upon the relative proportions of the two phases. Careful microscopic studies permit identification of pearlite structure relics even in a totally corroded iron object. (Knox, 1963)

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Incontrovertible proof of deliberate carburization can be derived from objects made by laminating layers of iron of varying carbon contents, for there is no reason to make such a structure unless the different properties of the layers were understood. Maddin et al. (1977b: 14) reported that “the earliest known laminated object is an Egyptian knife from the Ramesseum which probably dates to 900-800 BC”.

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Maddin further reported (1982) that quenching of carburized iron was practised by people in Cyprus and perhaps in Palestine by the eleventh century BC. A knife excavated from Idalion in Cyprus and belonging to a twelfth-eleventh century BC context showed surviving martensite and a form of bainite. An excavated pick from Mt. Adir in Northern Gallilee, Palestine, of the same age exhibited high hardness (545 DPH) corresponding to martensite, obtained by quenching from an austenitic condition, further tempered at a lower temperature. Homer described in his Odyssey (8th to 7th century BC) how a “black-smith plunges a screaming great axe into cold water treating it for temper and to make the steel strong”.

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To summarise, it is clear that iron known before 1200 BC was mostly wrought iron and ‘used sparingly, mostly for votive, amuletic or prized items of exchange’. (Maddin, 1982) Examples of deliberately carburized and quenched samples are available only from twelfth-eleventh century BC context onwards. The spurt in iron technology throughout the world is believed to be associated with the break of the Hittite empire and diffusion of technical know-how across the national borders.

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How Did the Iron Technology Arise in India?

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Gordon (1958) and Wheeler (1959) attributed the appearance of iron in India to the Graeco-Roman influences in the fifth and fourth centuries BC. Their theories have been discarded in view of the definite evidences regarding the presence of iron in India as early as 1200 BC, if not earlier. Some of the Iron Age Culture Sites in South Asia are shown in fig. 12.1. Prakash and Tripathi (1986) have documented the early iron age cultures, which could have been independent of each other, arising in five different zones of India. The sites corresponding to the five cultures (A to E) are shown in fig. 12.2. Some radio-carbon dates are indicated in fig. 12.3.

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Even if we ignore the early date of Ahar (1300 BC) which is disputed, it is evident that iron was discovered in India during or before the twelfth century BC. Of the five cultures:

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(A) Cairn Burial Culture in north-western India

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(B) Painted Grey Ware (PGW) Culture in north India

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(C) Black and Red Ware (B&RW) Culture in north-east India

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(D) Megalithic Culture of central India

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(E) Megalithic Culture of Peninsular India

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at least three cultures (B), (C) and (E) show dates before 1000 BC for the introduction of iron in India. Each one of these had developed distinct ceramic and chalcolithic traditions and therefore there is a strong case for the hypothesis of indigenous and independent development of iron technology in more than one Indian nuclear zone. N.R. Banerjee (1965) one of the celebrated early authorities on the iron age in India did not accept hypothesis as stated above.

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The Diffusionist Paradigm

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Banerjee reviewed the data available till 1965. Further excavations and discussions have taken place for more than a quarter of this century; therefore, we should not rule out the possibility of Banerjee substantially modifying his earlier conclusions (1965) which are present below.

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In the summary of his monumental treatise, Banerjee concluded (1965: 238-39):

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It was the Aryan settlers in India, who also used the PGW ceramic, that were the first to use iron in ancient India around 1000 BC, if not earlier. Around 800 BC or slightly earlier, the use of iron is testified among a people who buried fragmentary remains of their dead in

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Fig. 12.1: Map of the Iron Age Culture Sites in South Asia.

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Key : 1. Pirak, 2. Charsada, 3. Timargarha, 4. Taxila, 5. Rupar, 6. Bhagawanpura, 7. Panipat, 8. Sonepat, 9. Indraprastha, 10. Hastināpura, 11. Lalqila, 12. Jakhera, 13. Atrañjikhera, 14. Sravasti, 15. Jodhpura, 16. Noh, 17. Kauśāmbi, 18. Rājghāt, 19. Prahladpur, 20. Buxar, 21. Chirand, 22. Sonpur, 23. Rajgir, 24. Somnath (Prabhas Patan), 25. Nagara, 26. Ahar, 27. Nāgdā, 28. Ujjain, 29. Eran, 30. Nagal, 31. Ranjala, 32. Prakash, 33. Takalghat, 34. Mahurjhari, 35. Naikund, 36. Sisupalgarh, 37. Pochampad, 38. Bhongir, 39 Raigir, 40. Terdal, 41. Jevargi, 42. Piklihal, 43. Maski, 44. Yelleshwaram, 45. Nāgārjunakoṇḍa, 46. Tekkalakota, 47. Sanganakallu, 48. Hallur, 49. Brahmagiri, 50. Jadigenahalli, 51. Savandrug, 52. Kunnattur, 53. Pallavaram, 54. Sanur, 55. Perumbair, 56. Arikamedu, 57. Souttoukeny, 58. Mouttrapaleon, 59. Porkalam, 60. Alagarai, 61. T. Kalluppatti, 62. Adichanallur.

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Fig. 12.2: Map of the Indian Sub-continent showing some of the Archaeological Sites where Iron Age Articles have been found.

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Fig. 12.3: Radio-carbon Dates of Some Iron Age Sites in India.

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cairns in the borders of Iran and Pakistan. It is possible that they obtained their knowledge of iron from Sialk VI in Iran even as the Aryans of the Ganga Plains apparently did (emphasis supplied). A little later iron came into its own in West-Central India in the post-chalcolithic phase, as also in the megaliths of South India. In both cases, they (the inhabitants) owe not a little of their metallic inspiration to the northern plains. The possibility of a cultural influence direct from Iran (Sialk VI) being transmitted through the cairn burials to the megaliths of South India, cannot be ruled out.

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It is evident that Banerjee put lot of emphasis on the ‘diffusion from outside’ theory, the immigration of the so-called Aryans into India and the primacy of the iron-making traditions in Sialk VI. He referred (1965: 237) to the Hittites being defeated in circa 1190 BC, which set “in motion a colossal exodus of an Indo-European people in all directions with all their arts and sciences”, and resulted in “a new people occupying Iranian plateau, i.e., Sialk VI and introducing iron in the new habitat”.

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The iron-making technology could be consolidated in Sialk VI only long after the stated date of 1190 BC and we do not see how the knowledge of iron-making could diffuse from Sialk VI into India, if it ever did, before the eleventh century BC. Cemetery B of Sialk, exhibiting an abundance of iron, has been dated to c. 900 BC by Ghirshman (1954). Chakrabarty (1979: 355-58) explained how Gordon’s (1950) argument to establish a Sialk analogy for the cairn-burials in India was untenable, and yet accepted uncritically by Banerjee (1965) to build up his hypothesis. Prakash and Tripathi (1986) have quoted the C-14 date (of TF-191 sample) 1155 ± 110 BC for the PGW culture in Atrañjikhera and the twelfth century BC date of Tadakanhalli — both corresponding to the introduction of iron in India. The above-mentioned dates just do not seem to support Banerjee’s hypothesis and ‘eagerness to explain anything in terms of a migration from the West’.

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Like many other scholars, Shaffer (1984a) and Biswas (1990) have exposed the Aryan myth. Several eminent Indian archaeologists have fallen into this linguists’ trap. Banerjee himself (1965: 224, 232) has criticised H.D. Sankalia and D.P. Agrawal for equating Aryans with the Chalcolithic people and the Banasians respectively, and has approvingly quoted A. Ghosh who was “not so sure of the correctness of the attempted equation, and the old theory of the linguists”. Yet, Banerjee imagined that the ‘Aryans’ (whoever they were) came to India and introduced iron technology and PGW culture. Chakrabarti (1968) has given cogent arguments in favour of an eastern, rather than western, origin for the PGW, thereby negating the PGW-Aryan correlation.

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Banerjee (1965: 65-67) proposed that the megalith builders of Peninsular India might have picked up iron age culture around 800 BC either from the migrant Aryans or the cairn burial people of the North-Western India. The iron age of the cairn burial people in Pirak of Baluchistan, Swat Valley and Gufkral at Kashmir are all dated around 900-800 BC which is much later than the Tadakanhalli date of twelfth century BC. Thus, there was little possibility of the megalith builders ‘picking up’ iron age culture from the cairn burial people of the North-West. It could have been the other way round. There are four distinct possibilities regarding the origin of iron-age culture in the North-Western India: (a) indigenous development, (b) influence of the migrant megalith people from the South who shared the burial traditions, (c) influence of the Atrañjikhera/ Ahar PGW culture, or (d) influence from the Iranian culture of Sialk VI after ninth century BC. The possibility of Sialk VI iron-making tradition influencing the whole of India through the immigrant ‘Aryans’ or the cairn burial people may be safely ruled out.

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In this connection, we may refer to the bronze age iron from Afghanistan. (Shaffer, 1984b) Decorative iron ore nodules found at Said Qala Tepe and decorative iron balls and buttons, found at Said Qala Tepe and nearby Mundigak IV, have been dated to be around 2300-1900 BC. These early Harappan iron balls and buttons may be compared to the decorative pieces from the Mediterranean area dated third millennium BC, and indicate that wrought iron was not completely unknown in the ancient India of the Harappan era. However, these soft decorative materials could not replace bronze, and the real breakthrough or the advent of harder carburized iron took place in India, as in the rest of the world, only around 1200 BC.

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We do not deny the possibility of diffusion of knowledge in the ancient world. What we question is the romantic notion of the Central Asian ‘Aryans’ coming all the way to India with horses, conquering the land and spreading PGW and iron technology. Of course, the ancient chalcolithic cultures within and outside India were linked by trade, and therefore interactions must have taken place.

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We propose that diffusion of knowledge related to iron technology was not uni-directional. The technology grew in the ancient world in several phases, each covering centuries of time. We may identify at least five of these phases: (1) discovery of wrought iron and its ornamental use (3000-1200 BC), (2) discovery and use of surface-carburised iron, (3) use of forge-welded laminated sheets of carburised iron, (4) practices of quenching, hardening and annealing, (5) making of high carbon crucible steel.

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The first phase might have started in Anatolia, and yet in the bronze iron of Afghanistan (2300 BC) we have an example of early iron-awareness in the Harappan India. The second phase might have been indigenously developed in India in three nuclear zones viz., Gaṅgā-Yamunā doab, Karnataka Megalithic Culture and Bengal-Bihar area. Early iron in these areas, as we will record, are dated 1200-1000 BC. We do not have many dates outside India, earlier than the above, for iron deliberately carburised. We have mentioned (Maddin, 1977 b) ‘the earliest known laminated object’: an Egyptian knife dated 900-800 BC, which came centuries after Komaranhalli spear and Tadakanhalli axe in India clearly demonstrating lamination techniques in iron artefacts. (Agrawal, O.P. et al., 1990)

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We do not have any incontrovertible evidence of quench-hardening practice in ancient India as early as twelfth-eleventh century BC, the date corresponding to Cyprus knife showing martensite and bainite. (Maddin, 1982) But the credit of first producing crucible steel or ‘wootz’ certainly goes to India. These facts justify the notion of India entering the iron age substantially through indigenous efforts, occasionally receiving as well as transmitting technological details across its borders.

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The above ideas were accepted by most of the participants in the 1983 Poona Seminar. (Chakrabarty, 1985)

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