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History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13: 3.2 Metals and Metallurgy

History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13

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English

Contents

3.2 Metals and Metallurgy

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A large number of metallic objects made of Gold, Silver, Copper, Iron, Bronze and Brass etc. have been found at the Neolithic, Megalithic, Chalcolithic sites and others belonging to the latter period on the Indian Peninsula. Table 1 gives an overview of India’s cultural history and the chronology of the discovery and development of metals technology resulting into Copper Age, Bronze Age and Iron Age cultures. The archaeological approach to this type of classification suffers from the failure of direct application of 14C or other method of dating of the metallic objects. The dating of the metallic objects based on the strata of the excavation sites does not consider the probability of their earlier discovery, utilization and preservation. Spratt (1986), in his discussions on the innovation theory, has considered in detail the steps through which any new discovery and its introduction in the day-to-day life has to pass. According to him these stages are as follows :

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(1) Discovery - i.e. an addition on the body of technical or scientific knowledge.

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(2) Invention - i.e. the perception of the practical use of the discovered knowledge.

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(3) Development - i.e. small scale trials of manufacture and/or use of the invention.

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(4) Production and Distribution - i.e. mass scale availability and use of the material in the day-to-day life.

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The fifth step in this process is - obsolescence, when any innovation is rejected or surpassed in favour of another superior one, and this is the stage when a metallic object is generally found at the excavation sites except in the case of natural calamities. Thus we see that the discovery of any metallic or non-metallic object or artifact at any excavation site does not take into account the time gap comprising of the first three steps of any innovation and this may lead to inaccuracy in the determination of the exact age of metallic object and the era to which it actually

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Table 1 — Indian Chronology of Cultural History and Development of Metals Technology 1,2

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| Period | Cultural History of India | | | Introduction of Metals and Technology |
| Year | North | Central | South | |
| 1 M to 6000 B.C. | Pre-Harappan Aryans | Most probably Dravidian culture | Neolithic and Chalcolithic | Native Metal Au, Cu |
| 4000 B.C. | | | “ | Au, Cu and possibly Meteoric Iron |
| 2500 B.C. | Indus Valley Civilization (Glazed Pottery Culture) | Neolithic Culture | | Ag, Pb, As and Copper Alloys, Foundry Technology |
| 1500-2000 B.C. | Aryan Culture (Vedic Period) | Dravidian and Aryan Interaction | | Iron Age Culture, Steel and Metal Working Tech., Distillation |
| 600 B.C. | Rise of Magadh | — | — | Amalgamation, Soldering, Brass Gilding etc. |
| 500 B.C. | Persian Conquest and Buddhist Period | — | — | May be Wootz Steel (Matter and Atomic Theory) |
| 321-184 B.C. | Mauryan Dynasty Chandra Gupta and Ashoka Empire | — | — | Cupellation and other refining technology |
| B.C. | | Ayurvedic period | | — |
| O Christian era A.D. | | | | |
| 319-606 A.D. | Gupta Dynasty | — | Pallavas | Commercial scale Zn, Brass, Cireperdue Process of Casting |
| 600-710 A.D. | Invasion of Huns | — | Chalukyas and Chola Empire | Extensive use of Iron, Steel, Hg, Zn etc. |
| 1000 A.D. | Afghan’s Raid | — | — | -do- |
| 1100 A.D. | — | — | Hoysala | Brass and Bronze castings. |
| 1300-1572 | Mughal Sultanate | — | Vijayanagar | Bronze Guns and Metal craft |
| 1498 to 1707 A.D. | “ | Portugese in India, Mughals, Maratha | Industrialization of Iron, Steel, Brass and Bronze | |
| 1605-1761 A.D. | British Empire | — | French in India, War with Tipu Sultan | Modern Metal Tech. Iron Guns |

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belongs. Sorensen (1986) has pointed out that even the acceptance of any innovation may be delayed due to the socio-cultural set-up of the society, and hence its commercial utilization may be delayed. Saunders (1977) and McDonell (1984) have discussed the life cycle of the discovery of any metal and its objects. This cyclic discovery and discarding of metallic objects is shown in Fig. 1 with the introduction of one more step viz. ‘Preservation’. Here it is assumed that at the time of discovery of the metals they must have been a very scarce and costly commodity and hence there is high probability that the earlier metallic tools, hunting implements and other objects must have been preserved for centuries before they were destroyed or lost, and they could not have been thrown away like Stone Age tools. Fig. 2 shows the ‘time-gap’ between the discovery and utilisation of a number of inventions in Europe as plotted by Saunders (1977).

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As regards the initial scarcity and high value of the material a Śruti from Ṛgveda as translated by Banerjee (1929) and quoted by Kulkarni (1989) is given in Fig. 3, which mention the presence of steel and its high value in the Vedic period.

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The discussions presented here are based on the archaeometallurgical studies, which is a hybrid of the combined study of archaeological findings of metallic objects and their metallurgy. The desiderate for such evaluation are as follows :

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(i) occurrence of the mineral and their processing technology,

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(ii) details regarding excavation sites, settlement and industry,

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(iii) experience in the related field,

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(iv) evaluation of socio-economic network,

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(v) environment for the growth of the technology.

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India has been blessed with vast deposits of many minerals and precious stones and many of these have been in use even during the prehistoric era as ornaments

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Artefact / slag — smithing / use — PRESERVE / bloom / re-use — discard / lose / slag — smelting / potential artefacts / ore / corrosion — recovery / Natural World / display analysis

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*Fig. 1. Life cycle of archaeological metallic artifacts* Fig. 2. Delay-time for various innovations and their commercialization

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जरतीभिः औषधिभिः पर्णीभिः शकुनानाम् । कमरो अश्मभिः धुभिः हिरण्यवन्तभिच्छति इन्द्रायेन्दो परिश्रव ॥ ऋग्वेद ऋ 9.112.2

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कमार यानि लोहार लकड़ी के टुकड़े लोहे की खनिज के साथ रखता है । तालपत्र में लकड़ी के टुकड़े रखते होंगे । लोहे के खनिज के टुकड़े और तालपत्र लकड़ी के टुकड़े अर्क (asclepias giganta) यानि आकन्द वृक्ष के पत्तों से (पर्णीभिः) ढकते थे । खनिज के पत्थर (धुभिः अश्मभिः) लकड़ी के टुकड़े के साथ तपाने से जली हुई लकड़ी का कोयला (कार्बन) लोहे के साथ घुलता होगा जिससे लोहे का इस्पात में परिवर्तन होता होगा । कार्बन की मात्रा बढ़ाने के लिह शकुन यानि हंस पंछी के पर भी डालते थे । हंस के पंख में 90% वाष्पील द्रव्य और 10% कार्बन होता है या शकुन पंछी के परों का धौंकनी निर्माण करने के लिए उपयोग करते होंगे । ऋग्वेदकाल में इस्पात बहुत महंगा होता था । इसीलिए यह लोहार धन-सम्पन्न (हिरण्यवन्तं) व्यक्ति की प्रतिक्षा करता था ताकि उन्हें यह इस्पात बेच सके । इसी लेख में आगे बताया गया है कि उन्नीसवीं सदी तक भारतीय ऋग्वेद दिए हुए इस ऋचा में वर्णित पद्धति से इस्पात निर्मित करते थे ।

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Fig. 3. Sanskrit text regarding production of steel as mentioned in Rgveda in Rica 9.112.2 and source of pigments to decorate the human body as well as surroundings. The recent discovery of stone age tools by Rendell and Dennell (1987) at Jalapur and Soan syncline section near Mohenjodaro site belonging to the Shivalik period has been evaluated to be atleast two million years old i.e. one of the oldest in the world. Rendell and Dennell have opined that this important discovery may change the whole chronology of the evolution and dispersal of humanoids both in Africa and Asia, and possibly even the cultural history of the whole world. So far as the use of metals is concerned the oldest archaeological finding is at the sites belonging to the Harappa and Mohenjodaro culture and at some ancient cairn burials of South India. These sites have been rich in Gold, Silver, Copper and Bronze artifacts. The technological skill of the ancient craftsmen is evident from the famous bronze statue of the dancing girl found at Mohenjodaro and their skill to drill fine holes in mineral beads using a fine hollow metallic drill. The Mohenjo-daro bronze dancing girl was presumably made by the cireperdue process of casting.

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The Vedic scripts are full of the mention of Au, Ag, Cu, Fe and their alloys as well as their use in various religious rites. Prakash, S. (1965) has described a true ancient scenario by mentioning that in Vedic period all the science has grown with the Yajna which had almost become an open air laboratory and observatory. He has also warned that one has to be cautious while using the Vedic terminology which are markedly different from the terminology evolved in different disciplines of knowledge at a latter stage.

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The social life of the Vedic period has been mostly agriculture based and people had great faith in the religious rites and the philosophy of life. The scientific principles mentioned in the four epics might have been a part of their daily routine. While it had helped in maintaining the socio-economic order and preservation of culture it also had prevented the learned craftsmen from the preparation of written records of their experience and knowledge which were generally transmitted from father to sons and other members of the family or clan.

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There is no doubt that during the Vedic period the opportunity and the atmosphere were congenial for experimentation and development of new technologies, but owing to the religious beliefs and rituals associated with each experimentation, the free dissipation of the knowledge was prevented. How long this tradition has been in-vogue before the written records of these epics and processes were prepared is difficult to be decided and hence the exact history of the discovery of the metals and metallurgy in the Indian Subcontinent is not known. But it is certain that many of the common metals were known during the Vedic period and they were being used for the manufacture of various tools used for agriculture, defence, and transport by land, sea and probably also by air (vimān) using steam and other energy sources. The need for development of such technology has been described in Rgveda, Śruti 1.1, 1.3.1, 1,3.2. and in Yajurveda 1.4 and 4.33.

Discovery of Metals

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So far as the discovery of metals and the development of metals technology is concerned the universal opinion is that the focal point of these discoveries is Iran and its nearby area and in India the metals technology has been introduced by Aryans or Hittites who migrated from that area, but in a recent lecture Sharma,R.S.(1988) has opined that Aryans were originally Indians and most of the discovery of metals technology is indigenous. It is an universal belief that native metals like Gold, Copper and probable Meteoritic Iron have been the first to be discovered as early as 6000 to one million years before Christ.

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The golden yellow glitter of the native Gold has been probably the main force behind the development of the metals technology although this has been a worthless metal for the Stone Age men who wanted to fabricate war tools like arrows, axes and hammers from this metal. Mahamud (1988) has rightly mentioned that the glitter of Gold has been destined to play the most sinister role in the history of mankind and for the sake of possession of this metal many blood thirsty wars have been raged and monstrous crimes committed.

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According to Prakash, S. (1965) the discovery of fire (4000 B.C.) has played a vital role in the extraction and processing of metals. Atharvans or Angiras or Athar Vangiras are supposed to be the first to discover the fire. It is believed that the legends associated with the Promethens in the Greek Mythology actually had its

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अश्मा च मे मृत्तिका च मे गिरयश्च मे पर्वताश्च मे सिकताश्च मे वनस्पतयश्च मे हिरण्यं च मेऽयश्च मे श्यामञ्च मे लोहञ्च मे सीसञ्च मे त्रपु च मे यज्ञेन कल्पन्ताम् ॥ १३ ॥

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रत्नवान् धनवान् आत्मा । भुरिशतश्वरी । पंचमः ॥

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भा०—(अश्मा च) सब प्रकार के पाषाण, हीरे आदि, (मृत्तिका च) सब प्रकार की मिट्टियां, (गिरयः च) पर्वत, उनसे प्राप्त भोग्य पदार्थ, (सिकताः च) बालुकामय देश, (वनस्पतयः च) वनस्पतियां, (हिरण्यं च) सुवर्ण, (अयः च) लोहा, (श्यामं च) श्यामलोह, (लोहं च) लाल-लोह, कान्तिसार आदि (सीसं च) सीसा और (त्रपु च) टीन, रांगा आदि ये सब धातु भी (मे यज्ञेन कल्पन्ताम्) शिल्प, रसायन, भूगर्भ विद्या आदि के प्रयोग से मुझे प्राप्त हों । roots in India and the word Promethens comes from the Sanskrit word *Pra-Mantha* i.e. fire produced by manthan or rubbing action. In this context a *Sruti* from *Yajurveda* is quoted in *Fig.4* which clearly mentions the production of metals from *Yajña Kuṇḍa*.

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Fig. 4. Sanskrit text on the evolution of iron and other metals as mentioned in Yajurveda in Chapter 8

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Thus we see that ‘Agni’ has played a vital role in the extraction and working of metals. In the present chapter the metal technology has been mentioned from the point of view of their occurrence in nature, the scientific and technological feasibility of their extraction and study of the thermomechanical treatment of these metals for the production of various objects found in daily use of the ancient Indians.

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These descriptions are presented here in three sections viz. extraction of pure metals like, Gold, Silver, Copper, Iron, Tin, Lead, Zinc, Mercury etc., the technology of their alloying and the technology of fabrication and thermo-mechanical treatment.

Metallurgy of Pure Metals

(I) Gold

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According to Gowland (1912) and Bhardwaj (1979) it is extremely probable if not absolutely certain that Neolithic men would have first become acquainted with native Gold but they would have been disappointed in its use to shape hunting tools and war weapons. In our country not many Gold artifacts dating to Pre-Harappan period have been reported although in *Ṛgveda* Gold and its alloys with Ag and Cu have been mentioned in many places, such as, I-85.9, 88.5, 67.3; II-37.9; V-54.15, 57.1, 60.4; VIII- 7.27-32 etc. In Vedic literature this metal has been mentioned as *Hiranya* probably because of its high corrosion and oxidation resistance and the practice of its preservation through generations. The recurrence of this metal in the Chalcolithic period is more common and many artifacts have been reported from South India.

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This metal has its mesmerising power in its shining bright deep yellow colour which has not got tarnished even by the stains of human blood. In human civilization it has been named as the most sinister and deadly metal although due to its ductility and softness it had proved worthless for making any war weapon. This is so ductile that one gram of the metal can be drawn into more than 1.24 km long wire without any intermediate annealing.

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Marshall (1902-1903) has remarked that the Gold frontlets or dead man’s mask of the Adichanallur excavations are made of so flimsy gold leaf that in all probability they could not have been used in real life and these have been most probably used as substitutes for the dead. This also indicates the economic aspects of this metals use in the ancient times. The custom of tying gold plates or ‘Diadams’ is still prevalent in some parts of Madurai, and in North India it is customary to put a small piece of the metal in the mouth of the dying person.

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Native Gold has been found in this country in three forms :

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(1) Alluvial sedimentary deposits at shallow depth in the river basin. In Nilgiri hills such deposits have been worked upto a depth of 25 m or more.

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(2) As fine particles mixed with the river sand. Rivers of Sindh, Sutlaj and other rivers of Kashmir, Ganges, Swarna Rekha, Godavari and many other rivers of South India have been reported to carry gold fines in their sand. Kuppuram (1983) has reviewed such deposits in great detail.

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(3) As metal nuggets and streaks in quartz veins at Kolar and Hatti Gold Mines.

(1.1) Process of Extraction

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The most common process of separation of native Gold from the sand and alluvial soil or quartz rock has been by gravity separation or panning. In this process the quartz rock or the hard soil is first crushed to fine size to liberate the gold particle and then separate it by suspending the mixture in water.

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When the pan containing the suspension is agitated under water gold particles settle at the bottom of the pan and the sand and soil are washed away. For large scale working big pans were hung in the river water through a sling so that the mixture could be easily agitated. After the Gold particle was separated from the gangue (Qz and clay etc.) it was sold to the Goldsmiths for melting, refining and shaping of the metal. Dikshitar (1951) has mentioned that the labourers employed for Gold washing were known as ‘Sonwals’. McCrindle (1901) has mentioned that in Assam Gold Washing was being carried out at Suparnakudya (now Sonkudita) even in the 18th century and Sonwals used to pay custom duty annually to the Government in the form of Gold fines worth Rs.5/- During the Ahom’s rule about 10,000 people were employed in this trade. Sharma (1992) has reported that gold panning is being carried out even today by tribals of Rajgarh from the Eeb river, a tributary of Mahanadi and they are able to extract 4200 kg of gold per annum.

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The second process of extraction of this metal is by the process of amalgamation with Mercury and recovery of Gold by evaporation and distillation of Hg. This process has also been known to the ancient craftsmen and it was also used for gilding of objects made of copper, bronze and brass etc.

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Kolar and Hatti Gold mines were being worked even in the prehistoric times and as mentioned by Rao, S.R. (1973) the spectral analysis of the Gold objects of Indus cities and Kolar have shown high degree of similarity. Both the metals are in alloy of Au-Ag known as ‘Electrum’ instead of pure Gold. It has been proved beyond doubt that the South Indians had learnt the technology of mining Gold at these mines and established the smelting technology on commercial scale and the metal was being traded through Lothal by sea to Harappa, Mohenjodaro and even Egypt, Greece and Rome, Africa etc. even as early as 2500 B.C.

(1.2) Technology of Gold Working

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Most probably the first Gold piece used for shaping into a simple ornament like spherical or cylindrical bead or a wire for making bangles was a small nugget but latter-on smelting and refining techniques were developed. Pure Gold melts at 1063°C which could be achieved easily in charcoal fire. The Gold sand obtained by panning was melted in a crucible and refined by the addition of fluxes like borax and a mixture of Ammonium Chloride, Borax and Ammonium nitrate in the ratio 6:1:3. The method of separation of Silver from Gold was known as ‘Niyaria’ and the craftsmen practicing the separation of Gold and Silver were known by this name. Even today about 300 families in Mirzapur are practicing this trade for separation of various metals like, Au, Ag, Cu, Ni, Zn, brass etc. from the dross obtained from parent metal industries.

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The purified metal bar or ingot was worked by forging, punching, embossing etc. for the production of various ornaments having intricate designs. Even rolling and wire drawing was known to the ancient craftmen. Gold coins were either made by die casting in clay moulds or by the technique of punch marking and the quality of the metal was judged with the help of ‘Touch Stone’ and coin’s weight was accurately measured. *Arthaśāstra* of Kauṭilya gives detailed account of the knowledge of minting of coins and production of other objects and the technology of gem setting. They had also learnt to produce Au-Ag and Au-Cu alloys and the use of gold solder (Au:Ag, 8:1) and the ways to improve the golden colour finishing of the joints as early as the vedic period. Today it is well known that Au-Ag have a Eutectic type phase diagram whereas Au-Cu have complete solid solubility and alloying with these metals impart strength, hardness and various shades of colours to the metal as well as lower the melting point of the alloy. As mentioned earlier the technique of Hg amalgamation and gilding was also known to the Indian craftmen from the very early times.

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As regards the trade with foreign countries Prakash, S.(1965) quotes Greek and Roman historians giving an account of the Indian Gold and Silver. Curtius Strobo and Philostratus mention the use of these metals in Ancient India. The accounts of Old Testaments show that Ophir mentions the export of Silver and Gold from India. Megasthanese has also mentioned the mining of these metals in various parts of India in the Neolithic-Chalcolithic and Megalithic period. Allchin (1968) has mentioned that Greek Drahams and Roman Dinars made from Indian Gold were in circulation for trade and often smelted for reuse. During the period of Asokan Empire its capital was known as *Suvarnagiri* and it was known for the Golden splendour.

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*(II) Silver and Lead*

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Sneed et al.(1954) and McDonald (see Butts and Coxe, 1967) have mentioned that just as *Svarṇa* (Gold) has been related to Sun or Sanskrit word *Jval* (to shine), the brilliant white metal silver has been related to Moon and earlier it was called luna. Silver nitrate is still called Lunar Caustic. The Latin name ‘Argentum’ also has its origin in Sanskrit and it comes from the Aryan origin, meaning shining white metal.

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This is the second metal to have attracted the fancy of ancient Indians as a domestic metal which had no value for the manufacture of tools and weapons. The introduction of this metal in the ancient Indian Culture is relatively late because of its non-availability in the nature as virgin metal, i.e. very rarely it is found in the native form. McDonald writes (see Butts and Coxe, 1967) that the discovery of virgin Silver was probably due to the natural fire in some forest where the exposed Argentiferous Galena (mixed sulphide mineral) was roasted and then reduced resulting into the separation of this metal. Archaeologically speaking very few silver artifacts have been found dating back to Harappan period. A silver dagger belonging to 2700 B.C. from Harappa is being preserved in the National Museum, Delhi.

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Since Silver (M.P. 962°C) has been found to occur in nature either as AgCl (Cerasgerite) or Ag₂S (Argentite) associated with Galena and/or Sphalerite or mixed sulphide ores, the extraction of this metal is said to be started in 3rd or 4th Millenium B.C. with the development of the technique of treatment of sulphide minerals viz. roasting and reduction smelting. During the extraction of lead from PbS or PbO, Ag₂S also gets decomposed and reduced easily (at 470°C) and it readily alloys with metallic lead at 1000°C hence the metallurgy of lead is being described along with this metal.

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Lead artifacts have been reported from the Harappan period, although, due to its softness, it did not find much use in this period. It is one of the softest and heaviest metal having shining grey lustre which leaves a black streak on paper.

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It is so soft that it can be scratched even with nail hence it’s use has been mostly for the manufacture of cheap jewellery dies or pattern for shaping other metals, and as a hardner in copper alloys. In South India lead coins have been in use in Ist-2nd century B.C and it was the chief coinage metal for considerable time. It melts at 327°C and its B.P. is 1525°C. Besides PbS (Galena) it also occurs in nature as PbO i.e., Massicot and Litharge (Yellow in colour), PbCO₃ or Cerussite and white lead PbCO₃.Pb(OH)₂ (white powder) or PbSO₄.PbO (white pigment). Lead might have first been recognised as these coloured pigments used for body decoration and during use it might have fallen in the compfire producing metallic lead, because these minerals get decomposed easily to PbO and subsequently reduced to liquid lead at 500°C. The reactions occuring during the roasting of Galena are -

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2PbS + 3O₂ → 2 PbO + 2SO₂ ...(1)

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PbS + 2PbO → 3Pb + SO₂ ...(2)

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and finally PbO is reduced by C at 500°C or by CO even at lower temperature.

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PbO + C → Pb + CO ...(3)

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PbO + CO → Pb + CO₂ ...(4)

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Since liquid lead readily alloys with silver one of its major use was to first produce this alloy by coreduction of Pb and Ag minerals and then produce pure Silver by the process of cupellation. Bhardwaj writes that these processes were known during the Harappan period.

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*(II.1) Occurrence of Silver and Lead Minerals*

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In Indian subcontinent Galena is found in Rajasthan at Zawar and in small amounts in Kashmir, Garhwal in Uttar Pradesh, Bihar and Kerala. One of the biggest deposits of Galena and Ag₂S (Argentite) is found in Burma at Bawduin.

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Such deposit of Argentiferous Galena is found in Zawar and it has been reported to occur in Bihar, Orissa and Kamalpura. Sarkar (1971), and Butts and Coxe (1967) have reported large deposits in Burma at the Namtu and Bawduin mines where signs of ancient working of silver and lead have been found, and Burma is one of the major silver producer even today. Silver has been also reported to be produced at Ananthpur Gold field in Andhra Pradesh. There has been also evidence of the trading of Spanish Silver in exchange of Indian species.

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*(II.2) Production of Lead and Silver*

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As discussed earlier PbS after roasting gets converted into PbO and this can be easily reduced at 500°C to molten lead. The process used in ancient India at Zawar was most probably ‘Ore Hearth Process’ where the roasting and reduction of rich Galena is carried out in an open pit furnace. Fig.5 shows a sketch of such a furnace as reported by Raistrick (1927) and referred by Tylecote (1976). In such a furnace temperature as high as 1000°C can be easily obtained under natural draft and the reduced metal flows out and gets collected in the front pit. At this temperature Ag₂S also gets decomposed, reduced and forms an alloy with molten lead. The details of this process has been mentioned by Sevryukov (1975).

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Silver metal was obtained from the alloy of Pb-Ag by reheating it in a shallow hearth furnace having the bottom prepared with bone charcoal. During remelting of the alloy it is subjected to oxidizing condition by blowing excess air when lead gets preferentially oxidized to PbO (litharge) which has a very low melting point. This molten litharge is skimmed off and partially absorbed by the furnace hearth. This process is known as ‘Cupellation’. At the end of the refining process purified liquid silver is tapped out and cast into ingots. Although no clear evidence has been found at Zawar of any such furnace or the remains of Litharge but it has been known in ancient times for the production of lead and silver. Litharge might have been reduced in another ore hearth furnace to produce metallic lead. Kautilya’s Arthasastra states the following details of the process of cupellation for the purification of silver.

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“The pure and impure silver may be heated four times with CuSO₄, mixed with powdered bone (*Astithutha*), again four times with equal quantity of lead and again four times with CuSO₄ (*Suskatutha*), again three times in a skull and lastly twice in cow dung. Thus purified silver is obtained. This process has been also quoted by Ray (1956) and Bhardwaj (1979). Bhardwaj (1979) has written that this process of cupellation for the production of Silver and Lead was well developed in the 2nd half of 3rd M.B.C.

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*(II.3) Mechanical Working of Pb and Ag and their Uses*

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As mentioned earlier Lead being a very soft metal it did not find much use in the early days but in the latter period it has been used for the manufacture of sanitary pipes, moulding dyes, thin wire or rod for applying surma and probably also as a Fig. 5. Early ‘Ore Hearth’ Lead Smelting furnace as described by Raistrick

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SW NE Bayle Hill Gunners Beck faggots, peat and ore stone wall round fire 2ft 0in C puddled clay melted lead openings for wind section on AB 5ft 0in A bowl shaped hollow pig B dry walling section on CD

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base material for engraving and embossing Gold and Silver sheets and foils. Jeyaraj (1990) has mentioned the use of cast lead coins in South India in the 2nd to 3rd century A.D. possibly belonging to Sangam period. Lead compounds also have been used for glazing potteries and in the manufacture of glass. Evidences have indicated the use of this metal to prepare Pb-Sn alloy used as solder to join pieces of copper and bronze. In latter period lead has been extensively used for preparing projectiles for slings and catapults, bullets, cannon balls and cast shots etc.

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The shining white colour, high corrosion resistance and the non-tarnishing properties of silver attracted the attention of the primitive men and they found its use in making ornaments, utensils, decorative pieces and other house hold articles. It has also been used for the manufacture of various weapons for decorative as well as ceremonial purposes. The high ductility of the metal permitted it to be forged into sheets and foils used for making utensils having intricate embossed designs, as a sheet covering on various wooden objects studded with jewels for the use of rich men and kings. Its very thin foil has been used to cover various food dishes. This metal has been found also to have medicinal properties and used in the ancient Ayurvedic medicinal system.

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The use of this metal as coins has been rather late. It is only in 600 B.C. that punch marked coins have appeared and in the latter period Silver has been popular as coinage metal. In the Gupta period Copper has been deliberately added to economise the consumption of silver as well as increase the wear resistance of the coins. Kauṭilya’s Arthaśāstra gives a vivid account of minting such punch marked coins. In the latter period other coins have been produced by rolling silver pieces into sheets of uniform thickness and cutting it into equal square pieces. The identification marks were punched on these pieces and their weight was controlled by cutting away the metal from one corner. In recent years Saran (1985) and Prasad, B.(1990-91) have analysed and studied the microstructure of a number of Ag-Cu alloy coins from different heads and they found the alloy composition to be consistent in each group.

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*(III) Copper*

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In lithic societies the use of coloured minerals like iron oxide, lead oxide and blue and green coloured Azurite (Hydrated copper carbonate) has been very common as cosmetics, colours used for decorating hutment walls and pottery, and their use in religious rituals and funeral practice. It is possible that accidental fall of the copper mineral in the fire has given rise to the copper age around 4000 B.C. According to the archaeological evidences this metal is probably the fourth in the series to attract the attention of mankind and give a new dimension to the human culture by providing new fighting and self-protecting power in the hands of mankind.

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The discovery of this metal marks the beginning of the Chalcolithic period and the Copper Age when man started using metal instead of stone and clay to fabricate his hunting tools, domestic utensils and many other things like ornaments, decorative pieces, mirror etc. The properties of this ductile reddish coloured metal having a melting point of 1083°C were further improved in the latter period by alloying with Pb, As, Sn and Zn, and some of these produced yellow coloured alloy similar to that of Gold. Copper sulphate mineral was given the name ‘Fools Gold’ owing to its shining yellow colour.

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The first and oldest evidence of copper artifacts in India come from the Nal Cemetery dating back to 3rd M. B.C. i.e.. the same period as in Iran. Tylecote(1976) is of the opinion that the technology of production and use of copper in this country was imported from South Iran along the Persian Gulf i.e. by sea route rather than over the difficult land route through Northern Baluchistan or Afghanistan. If this is true the Indian society developed at Lothal had trade links as early as 3rd M. B.C. i.e. even earlier than Harappan period. Forbes(1964) has mentioned that King Devius of Iran had a brass cup dating to 522 to 486 B.C., and the origin of this cup most probably belonged to India. This leads to the conclusion that the process of extraction of copper was probably known to Indians much earlier than 3rd M. B.C. and it contradicts the views of Tylecote. The theory of indigenous discovery of copper production technology is further supported by the presence of 4.8% Ni and 2.14% Pb in the copper artifacts found at the Harappan sites, whereas the Iranian copper is rich in Arsenic. the copper sulphide ores found at Khetri and Maubhandar have been found to be rich in nickel.

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Rai(1965) has mentioned the discovery of hollow copper, Gold and Silver beads belonging to the Harappan period which were manufactured in two halves and then soldered together. These beads have been threaded in copper wire to form a necklace. At Chinkudaro three types of copper bangles belonging to the same period have been reported. Out of these one type was made from 3.5 to 5.05 mm round copper wire, the second type was semicircular in cross-section with the flat side making the inner side of the bangle. The third type had been hollow from inside and it was made by shaping copper sheet. At Lothal a thin hollow copper pipe has been found which was probably used to drill holes in Gems and glass beads. The massivity of copper objects made in the past can be judged from the tapered copper bolt 620.0 mm in length and having 49.15 mm diameter at the two ends and 56.9 mm at the centre. This bolt has been recovered from an Ashokan pillar found at Rampurva near Nepal dating back to 3 century B.C.. and it is now preserved in the Calcutta National Museum. This bolt requires atleast two persons to lift it. The copper Chariot from Daimabad Hoard has been cast in one piece by the cireperdue process. It is now preserved at the Prince of Wales Museum, Bombay.

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The use of copper has been mentioned as Lohitya and Loha in Vedas and other ancient literature. This has been reviewed in great detail by Kulkarni(1989) and Joshi(1970), Bhardwaj and many others. Rasa Ratnasamuccaya gives a vivid account of the processes of extraction of copper and its use in Ayurvedic Medicinal system. In this book copper has been classified into two qualities i.e. one the pure (Red) copper from Nepal and the other impure or black copper (Malecch). The Nepal copper was of high purity (99.5%), brick red in colour and very ductile whereas the impure copper contained copper oxides and other impurities like Pb, Sn, As, Zn etc. which made it hard and brittle.

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*(III.1) Natural Resources and Extraction of Copper*

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Copper occurs in nature in native form and most probably man's acquaintance with this metal was in this form, which could be hammered i.e. cold worked to make various hunting tools etc. which could replace the crude stone objects. In India the occurrence of native copper is very rare and there is a possibility that Indian craftsmen got introduced to this metal by chance reaction between copper bearing minerals like Malachite, Cuprite and Chalcopyrite and charcoal fire. The chemical formula of the copper minerals is given below:

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Malachite - CuCO3.Cu(OH)2

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Azurite - 2CuCO3.Cu(OH)2

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Cuprite - Cu2O Chalcopyrite - Cu.FeS2 Hydrated Blue Vitriol - CuSO4.5H2O

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Besides these there are many other minerals bearing copper as chloride etc. The most common mineral of copper found in India is chalcopyrite but others are also found as placer deposits. Chalcopyrite has been reported to occur at Khetri in Rajasthan, Surda, Mosabani and Rakha in District Singhbhum of Bihar, Almorah in U.P., Sikkim and Nepal.

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The archaeological survey has indicated that copper was being extracted at Udaipur, Debari, Dilwara, Kedolai, Jhunjhunu, Khetri and Alwar in Rajasthan and Ahmednagar, Daimabad and Ahar in Gujrat and Maharastra region. Singhbhum copper deposits were also being worked in the past and most probably the copper in the Gangetic plains came from here through the river route, whereas the copper objects found in Sindh, Haryana and Rajasthan came from the ancient mines of Khetri region and Aravali hill deposits. Fig. 6(a & b) shows picture of the ancient mining sites located near the modern Surda mine of Singhbhum. Copper working site dating back to 1000 A.D. has been reported by Mohammad (1961) at Agnigundala in Andhra Pradesh. The deposit extends over 3 km and upto 3 km depth and it is surrounded by the entire working starting from mining to pounding stones, washing tanks and melting furnace as well as slag dumps etc.

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The first mass scale copper extraction process might have been carried out by carbothermic reduction of Cuprite in a bowl or small shaft furnace because this does not involve the complicated treatment of sulphide minerals. A comparative stepwise flowsheet is given below :

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(i) Cu2O+C (wood charcoal) heat 2Cu+CO (Reduction of oxides) (ii)(a) CuS.FeS+O2 → CuO +FeS+SO2 O2 → CuO+Fe+SO2 (Roasting), and (iii)(b) 2CuO+2FeO+2C+SiO2 → Cu+2CO +2FeO.SiO2 (Reduction).

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Thus we see that the production of copper from Chalcopyrite is a two step process involving precise control of the thermochemistry. Moesta and Schlick (1989) and Yazawa (1980) have discussed the thermodynamic limits of the roasting and reduction of copper sulphide in great detail. Fig. 7 gives the phase diagram for the Cu-Fe-S-O system as calculated by Yazawa (1980). These studies have confirmed that for dead roasting a temperature higher than 850°C is required and during this process iron acts as sulphur scavenger helping the conversion of CuS into Cu2O and CuO, and during reduction FeO reacts with SiO2 to form 2FeO.SiO2 (Fayalite) slag which has lowest melting point of 1177°C. The calculations have also shown that although at 1000°C copper oxides gets reduced to metal but the slag phase remains solid, and that molten metal separates out only at temperature above 1250°C. Based on the occurrence of 1.08 to 1.88% iron in the copper objects from Ahar, Chakraborti (1983) and Tripathi (1985) have formed the opinion that copper and iron oxides can be simultaneously reduced easily, and in presence of copper the reduction of iron oxide is possible only at very low pressure of oxygen (log PO2 = 10-3 atmosphere) normally not possible to attain in the low shaft furnace. Maddin (1982) and his group have conducted some experiments on the ancient reduction technology and they have found that during the reduction of roasted Fig. 6. Photograph showing an ancient copper mining (a) trench, (b) mouth of shaft at Surda Mines, Singhbhum Fig. 7. Cu-Fe-S-O equilibrium diagram (at 1300°C) indicating the instability of metallic iron in presence of CuO, and ultra low oxygen pressure required for its production

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Sulfur-oxygen potential diagram for the system Cu-Fe-S-SiO2 at silica saturation produced under the thermodynamic conditions of the ancient copper smelting furnace of the Ahar culture.

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chalcopyrite all the iron oxide forms 2FeO.SiO2 slag with silica, and they did find some prills of iron embedded in the slag.

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The chemical reactions taking place during the production of copper are as given below:

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i) Roasting reactions

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4CuFeS2 → 2Cu2S + S2 + 4FeS ..(1)

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2FeS → 2FeS + S2 ..(2)

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4CuS → 2Cu2S + S2 ..(3)

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S + O2 → SO2 ..(4)

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4Cu2S + FeO → Cu2O + FeO ..(5)

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2FeS + 3O2 → 2FeO + 2SO2 ..(6)

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ii) Reduction reactions

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Cu₂S + 2CuO → 6Cu + SO₂ ..(7) Cu₂O + C → 2Cu + CO ..(8) 2FeO +SiO₂ → 2FeO.SiO₂ (slag) ..(9)

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Percy (1861) and Tylecote (1962) have mentioned that in Sikkim evidence of old copper working has been found and there powdered ore was mixed with cow dung, balled and roasted. Then the roasted ore was melted with charcoal in a shaft furnace to produce copper. At Khetri also similar process was in practice as quoted in Gleaning in Science (1831) and by Anon Brook(1964).

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The analysis of copper smelting slag at various sites have been found to contain Fayalite as the major constituent and the slag from Rajghat contained CaO.SiO₂ also, besides other impurities like Al₂O₃, MgO, the CuO content of the slag was 1.05 only.

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*Rasa Ratna Samuccaya* has mentioned a number of processes for obtaining pure copper from chalcopyrite by smelting small charges in crucibles as reviewed by Jha (1990). He has conducted detailed experiments on the process of extraction of copper from chalcopyrite following the Ayurvedic route and using Lemon juice as the reductant. In this process after purification (sodhan) of chalcopyrite following the Ayurvedic process the ore mineral was roasted at 750-900°C adding lemon juice during the process. The process of roasting was alternated by tritaturation of the charge. In this process 100 c.c. of lemon juice was added per 100 gm of the ore. During the roasting process Cu and Fe get converted to citrates. The roasted ore was mixed with 25% Borax (flux) and more of lemon juice and the mixture was pressed into 20-30 mm balls. These balls were dried in Sun and then melted in Silimanite lined crucibles at 1250°C. There are four stages of the process of production. On carrying out the melting at 1250°C almost sulphide and gas free copper button separated from the liquid slag was obtained. *Fig. 8* shows the microstructure of the copper button showing dendrites of copper and some inclusions of CuS, CuO and slag.

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Another process mentioned in the *Rasa Ratna Samuccaya* is based on the precipitation of Cu from blue, vitriol solution (CuSO₄) by the process of cementation. In this process concentrated CuSO₄ solution was kept in an iron bowl, where on the surface a copper layer was formed following the reaction given below:

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CuSO₄ + Fe → FeSO₄ + Cu (10)

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After some time when a thick layer of pure copper particles was deposited on the iron surface the solution was removed and then copper was collected by scrapping it away from the iron surface. This pure copper was carefully washed with water free from (SO₄) and used for the preparation of copper *bhasma*.

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(III.2) Thermo-mechanical Treatment of Copper

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Copper, a brick red coloured metal has a melting point of 1083°C and it is very ductile in nature. This can be easily cold or hot worked to give any shape like rod, plate, wire and sheet etc. Hence, it has been extensively used in the past for the manufacture of domestic utensils, jewellery as well as for covering the wooden surface and engraving it for decoration and preservation of wood pannelling. The work hardening effect can be easily removed by annealing at 700-800°C in cowdung fire to produce metal having stressfree recrystalised grain having high ductility. The archaeological evidences have shown that this metal was shaped into various objects by casting into stone and clay moulds, hot and cold forging and soldering or rivetting to join two metal pieces. The ancient craftsmen had a flare to produce beautiful designs on the copper objects by embossing, engraving and gem setting. Beautiful objects having carvings inlayed with Gold and Silver wire and hot enamelled have been also found in latter stages. Copper being soft metal the sharp edge of the hunting tools and war weapons were hardened by cold working till the technology of production of bronze and Cu-As alloys were developed, which were much harder than the cold worked copper. On polishing the surface of copper could be given a highly shining polished finish which was being used as a mirror in the royal families. The Gold coating of copper objects by the process of amalgamation was also in the practice to produce various decorative cheap articles made from copper but having a golden finish.

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Fig. 8. Microstructure of copper button produced by the Ayurvedic method showing dendrites of copper and presence of CuS, CuO and slag inclusions, Mag. x 100

(IV) Iron and Steel

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The discovery of iron and its technological development on the Indian subcontinent has raised many questions because of the lack of archaeological proof dating back to those existing at Lustrian in Iran and other centres of ancient civilization. There is a total absence of iron objects at the Harappa and Mohenjodaro sites but the recent excavations at Lothal,Ahar(1300 B.C),Gufkral (1300 B.C.),Atranjikhera (1025 B.C.),Tadkanhalli(1000 + 150 B.C.) Hallur (1000 to 900 B.C.) and Khairadih (1000 + 100 B.C.) have pushed back the beginning of the iron age to the same period as those outside India. *Fig. 9* shows the 14C dating of the iron objects found at some of the important excavation sites of India and its shows a definite trend of simultaneous development and appearance of this metal all over India. *Table 2* gives the chronology of development of iron tools and other objects during the early, middle and later stages of the development of iron age in the country. This table clearly shows a gradual widely spread development of the use of iron which is possible only under the conditions where the knowledge of the use of these artifacts is lacking. This indicates that in all probability the iron technology in India is independent of the copper technology and it might have been developed even before copper.

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This hypothesis is further supported by the nature of the deposit of the mineral of the two metals, and comparatively easy method of obtaining iron from the oxide

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Fig. 9. 14C dating of some of the iron objects found at different archaeological sites in Indian subcontinent Table 2 — Various tools and implements appearing at the three stages of iron technology growth

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| Tool Type | Name of Tool | Early Stage | Middle Stage | Late Stage |
| **Hunting Tools** | | | | |
| | Spear heads | * | * | * |
| | Arrow heads | * | * | * |
| | Points | * | # | # |
| | Socketed tangs | * | # | # |
| | Blades | * | * | # |
| | Spear lances | # | * | # |
| | Dagger | # | * | * |
| | Sword | # | * | * |
| | Elephant goad | @ | * | * |
| | Lances | @ | @ | * |
| | Armour | @ | @ | * |
| | Helmet | @ | @ | * |
| | Horse bits | @ | @ | * |
| | Caltrop | @ | @ | * |
| **Agricultural Tools** | | | | |
| | Axes | * | * | * |
| | Sickles | * | * | * |
| | Spade | @ | * | # |
| | Ploughshare | @ | * | # |
| | Hoe | @ | * | * |
| | Chisel | @ | * | * |
| | Pick | @ | # | * |
| **Household Objects** | | | | |
| | Knives | * | * | * |
| | Tongs | * | # | # |
| | Discs | @ | * | # |
| | Rings | @ | * | # |
| | Spoons | @ | * | * |
| | Sieve | @ | @ | * |

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| Tool Type | Name of Tool | Early Stage | Middle Stage | Late Stage |
| | Cauldron | @ | @ | * |
| | Bowls | @ | @ | * |
| | Dishes | @ | @ | * |
| Building Materials | | | | |
| | Rods | * | # | # |
| | Pins | * | # | # |
| | Nails | * | * | * |
| | Clamps | * | * | * |
| | Pipes | @ | * | # |
| | Sockets | @ | * | # |
| | Plumb bob | @ | * | # |
| | Chains | @ | * | * |
| | Door hooks | @ | * | # |
| | Door handle | @ | @ | * |
| | Hinges | @ | @ | * |
| | Spikes | @ | @ | * |
| | Tweezers | @ | @ | * |
| | Anvils | @ | @ | * |
| | Hammers | @ | @ | * |
| | Scissors | @ | @ | * |
| | Saw | @ | @ | * |

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* indicates definite existence; @ indicated non-existence;

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indicates that confirmed data is not available.

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ore than copper from the sulphide ores. In India while iron ore Fe2O3 and Fe3O4 are occurring as surface deposits embedded in the Quartz and Dolomite minerals below the gound level. This aspect of the discovery and development of iron technology has been discussed in detail by Prakash, B. (1990) and from this view point the earlier attempts of correlating the discovery of iron to P.G.W. and N.B.P. in the Northern India seems to be inaccurate, although iron implements appear along with these potteries at many sites.

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The survey of ancient literature has provided ample proof that iron and steel making technology and their difference has been known in the Vedic period (vide reference on Rgveda and Yajurveda) and may be even earlier. These evidences also support the hypothesis of Sharma R.S. that Aryans were the original inhabitants of India and this also supports the use of iron both by Aryans and Dravidians even in the pre-historic period. As cited earlier Indians of the Vedic period were using steam powered transport vehicles and they were capable of producing many types of war weapons and agricultural tools which is possible only by the use of iron and steel. Prakash and Tripathi(1986), and Kulkarni(1989)have published a detailed review on this metal and listed chemical composition of many of the iron objects. These objects have carbon content of 0.03 to 1.3% and they are basically Fe-C alloys. The *Suśruta Saṃhitā* has mentioned the method of fabrication (700 B.C.) of more than 100 surgical tools made of Fe-C alloys and the process of heat treatment to obtain razor sharp edge capable of splitting hair into two halves longitudinally.

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*Fig. 10* gives the sketch of some of these tools prepared on the basis of their description in the text. *Fig. 11* shows the collection of iron swords and daggers etc. collected from the excavations at Tinnevelley dating back to 400 + 100 B.C., and *Fig. 12* and 13 show various iron objects found at Atranjikhera dating back to 1200-1000 B.C.

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Some of the massive iron objects manufactured in India in the Christian era have no parallel in the world, such as the famous Iron Pillar at Delhi (4th century A.D.) weighing 6000 kg, Iron Pillar at Dhar (12th century A.D.), weighing 7000 kg, 29 iron beams at Konark in Orissa (9th century A.D.), of which the longest one measures 11000 mm in length and 175 by 197 mm in cross section weighing about 3000 kg, the iron trident at the temple of Achaleshwar on mount Abu, the iron pillar at Kondachari and the iron trident at the temple of Tanginath near Bishunpur in Bihar. Some of these are shown in *Fig. Nos. 14 to 18*. The massivity of these objects and their high corrosion resistance have kept the modern metallurgists and technologists wondering about the manufacturing and processing details as well as the cause of their such high corrosion resistance.

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*Fig. 10. Sketch shows some of the surgical tools designed by Suśruta* (IV.1) Iron Minerals and Smelting Technology

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Fig. 11. This photograph shows some of the Iron swords and daggers found at Tinnevelley (400 B.C.)

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Iron occurs in nature mostly as Fe₂O₃(Hematite) and Fe₃O₄ (Magnetite) and some Pyrite deposits (FeS) have also been known. Besides this, in some parts of the world Meteoric Iron has also been found and used for the early war weapons. Iron of Meteoric origin is easily distinguished by its high Nickel content.

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India has been bestowed with one of the largest and richest deposits of Hematite, Magnetite and their hydrated forms like limonite etc. and these deposits are spread all over India. These deposits have been worked all over India to produce sponge iron or wrought iron using variety of furnaces and archaeological remains of a number of furnaces have been found at Nalanda, Naikund, Khairadih, Ujjain and many other sites. Fig. 19 shows a sketch of the reconstructed furnace dating back to 700 B.C. As can be seen this furnace has been constructed from prefabricated refractory clay blocks or bricks, whereas the furnaces used in Western Asia and Europe in the same period were either made by digging a hole in the earth or by arranging stone pieces to give the desired shape. These furnaces were generally used only once and then discarded after taking out the hot bloom. That is the [Figure: Iron Weapons : Period III: 1-8, Arrow heads; Spearhead; 10. shaft 1/2 Fig. 12. Some of the iron objects excavated at Atranjikhera (~1000 + 200 B.C.)]

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