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Minerals and Metals in Ancient India v2.c45.s9: Some Tentative Interpretations

Minerals and Metals in Ancient India v2.c45.s9

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Some Tentative Interpretations

v2.c45.s9.1

We may now attempt to provisionally interpret some of the *RRS* terms related to the ferrous materials. Nearly 2500 years before *RRS* was composed, India had made for the first time wrought iron by solid state carbothermic reduction process. The samples naturally contained some inclusions of slag.

v2.c45.s9.2

Over centuries, it was found that the soft variety of wrought or pure iron could be carburised by contact with hot burning charcoal, and this produced some hardening of the samples at least on the surface. Evidently, austenite, ferrite and pearlite phases were formed in the carburised samples. There was a reference to hot forging in the *Kauṭilīya Arthaśāstra* (7.3.8-9).

v2.c45.s9.3

तेजो हि संधान कारणम्। नातप्तं लोहं लोहेन संधत्त इति
*tejo hi saṃdhān kāraṇam । nātaptam lohaṃ lohena saṃdhatta iti*

v2.c45.s9.4

Third century BC Pandurajar Dhibi samples of sickle were found to contain 0.22 weight p.c. carbon and distinct grains of tempered martensite (De and Chattopadhyay, 1989) which must have arisen due to intentional quenching, hardening, and conversion from the austenite phase (solid solution of carbon in gamma-iron). Hadfield reported that the second century BC Taxilā samples contained 1.2 to 1.5 per cent carbon.

v2.c45.s9.5

We do not know when India started producing crucible or ‘wootz’ iron/steel which contained more than 1.7 per cent carbon. Probabaly this technology also was started before the Christian era, as inferred from the Greek and Roman travellers-cum-writers. Such a high percentage of carbon resulted in the cementite (Fe₃C) phase, which contributed to hardness as well as brittleness. The Wootz swords and implements could however be made ductile by careful forging at a not-too-high temperature of 650ºC-850ºC, when the coarse cementite grains were compressed and elongated in one direction, surrounded by pearlite and ferrite matrix. Reheating and quenching would result in some martensitic transformation. On selective etching, these ‘Damascus steel swords’ would show white cementite streaks. The finished product, a high carbon steel with cementite streaks in pearlite-graphite-martensite matrix possessed ideal combination of hardness (even at the edges) and ductility. These steel materials, sword, etc. were described as ‘of a dull blue colour, marked with ten millions of meandering lines’ which were the distinctive ‘damask’ or surface pattern of seggregated white cementite (Sherby and Wadsworth, 1985).

v2.c45.s9.6

The Gupta era (fourth and fifth centuries AD) in India witnessed spectacular iron technology in Ujjain, where big iron objects were forged in special furnaces. The fourth century iron pillar, now at Meharauli, Delhi, and the tenth century Dhar pillar (43'8" high, the highest in the world) of king Bhoja are unique examples of hot forging of wrought iron.

v2.c45.s9.7

Both Subandhu (AD 400) in his work *Vāsavadattā*, and king Bhoja (AD 1000-1055) in his *Yuktikalpataru* referred to iron works, pillars and *lohaśāstra* texts on iron technology. Subandhu specifically mentioned in his work the then knowledge on different kinds of magnets and magnetised iron. We have mentioned in the previous chapter Varāhamihira’s detailed description about quenching of steel swords (*Br. Saṃ.*, 50.23-26) which definitely resulted in martensitic transformation and hardening of steel. Uses of water, oil, milk, blood and other quenching media resulted in different rates of cooling and different degrees of martensitisation and hardening.

v2.c45.s9.8

With the aforesaid brief historical and technical discussion we may now interpret the *RRS* terms provisionally.

v2.c45.s9.9

Mundaloha was presumably wrought iron obtained by direct solid state reduction. The name probably originated from Mundiā, one of the metalsmith tribes in the district of Bastar, whose ancient iron-making process has been scientifically observed and recorded by Prakash and Igaki (1984). Low carbon materials *mrdu* was soft; *drutadrāva* is better translated as ‘softening quickly’ rather than ‘melting quickly’, since wrought iron would not have a low melting point. With more carbon, *kuntham* and *kaḍāram* varieties became less ductile. *Kaḍāram* was even brittle; black fracture indicated graphite at the interface.

v2.c45.s9.10

Tikṣṇam represented in general, carburised iron with appreciable hardness, which could be hypoeutectoid (less than 0.83 per cent carbon) or hypereutectoid (more than 0.83 per cent carbon) steel. *Pogaras* meant hair-like lines which may be surmised as white cementite streaks, coarse enough to be seen by naked eyes (microscope had not been discovered yet). In the *khara* variety, cementite *pogaras* were too fine to be seen, but the brittleness and the ‘mercury-like shining fracture surface’ were evident. In the *hṛnnāla*, *vājira* and *kālāyasa* varieties, hot forging and quenching had resulted in hardness as well as ductility. We have explained this point earlier while discussing the medieval practice of damascening of swords. The *hṛnnāla* variety was *chedane atiparuṣam* very hard to pierce. *Vājira* was described as *pogara vajra samkāśa sūkṣmarekhā* full of hard *pogaras* and overspreaded by dense thin linings. *Kālāyasa* variety was described (5.82) as

v2.c45.s9.11

नीलकृष्ण प्रभ सान्द्रं मसृणं गुरु भास्वरम्।
लोहाघाते अपि अभंगात्मधारं कालयसं मतम्।।
*nīlakṛṣṇa prabha sāndraṁ masṛṇaṁ guru bhāsvaram |*
*lohāghāte api abhaṅgātmadhāraṁ kālayasaṁ matam ||*

v2.c45.s9.12

bluish black, dense, smooth, heavy, bright and its sharpened edge not spoiled by hammering. This description is close enough to that of the damascened steel swords ‘of a dull blue colour and with meandering lines’.

v2.c45.s9.13

The technique of producing ‘Damascus steel and sword’ from Indian wootz was learnt and perfected by the Arabs in Damascus. Around the time when the RRS was written in India, the city of Damascus was conquered by Timur or Tamerlane (AD 1401), and the best metalsmiths were taken to Samarqand. (Pant, 1985) Thus, the Indian technology was gradually taken to the Middle East and Central Asia.

v2.c45.s9.14

The kāntaloha, as we have explained, was the iron made from magnetitic ore, and specially magnetised. Probably it was believed that iron made from magnetite and hematite had different properties. The different types of kāntaloha merely referred to the different levels of magnetisation. The classification under headings of bhrāmaka, cumbaka etc. had existed for at least one millennium before RRS. Subandhu (~ AD 400) had mentioned these types in his work Vāsavadattā.

v2.c45.s9.15

Rgveda to Rasaratnasamuccaya represents a wide time-span of three millennia, during which the Indian literature recorded the progress of knowledge in the areas of minerals, metals and alloys. Archaeological evidences of ancient Indian metallurgy are no doubt more direct and conclusive but are necessarily mute. The underlying philosophy and concepts, evident only in the literary evidences, would be discussed in the next chapter.

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