The history of civilization is in many ways linked to the story of the use of metals in antiquity. Although modern metallurgy has seen an exponential growth since the Industrial Revolution it is interesting that many modern concepts in metallurgy have their seeds in ancient practices that pre-date the Industrial Revolution. Metals were extracted and utilized in the past in stages progressing usually from the use of native metal, to those metals which could be smelted easily from ores, to those which were more difficult to smelt. The commonly used metals in antiquity include gold, silver, copper, iron, tin, lead, zinc and mercury. This brief review takes a synoptic look at some aspects of the early use of metal in a global perspective. It throws light on some of the achievements of ancient Indian metallurgists. Its heritage in metallurgy, medicine, mathematics and astronomy is a matter of pride for India.
Gold and Silver
The noble metals, gold and silver, are found in the native state, and as is well known, gold and silver were used to make jewelry and sheet metal due to the great ductility and lustre of the pure metals. Some of the early rich finds of gold artifacts were from the cemeteries in Bulgaria in Europe (5th millennium BC) with accouterments of hammered and sheet gold. Some of the most elegant gold vessels made by the repousse technique come from the Mesopotamia (ca 2500 BC). Spectacular gold castings are known from ancient Pharaohnic Egypt, such as the enigmatic face of the young Pharaoh Tutenkhamen (ca 1300 BC). Early gold and silver ornaments from the Indian subcontinent are found from Indus Valley sites such as Mohenjodaro (ca 3000 BC). These are on display in the National Museum, New Delhi.
Some of the most interesting artifacts of gold are the unique tumbaga alloys from medieval South America which are gold-copper-silver alloys of about 40% gold used for making castings and sheet metals. These were chemically treated to give a surface of pure gold. Also from South America comes unique evidence for use of the metal platinum in antiquity where the sintering of platinum granules with gold was practiced.
In antiquity gold would usually have been collected by panning alluvial sands from placer deposits. However India has the distinction that the deepest ancient mines in the world for gold come from the Maski region of Karnataka with carbon dates from the mid 1st millennium BC. A rather delightful piece of conjecture is that tales of Herodotus, the Greek, about ‘gold-digging ants’ from India refers to marmot, a type of rodent found in Afghanistan, who dig up the river sand which could then have been panned for gold by the inhabitants. Prof. R.K. Dube has produced literary evidence that the ants gold, refer to in the epic Mahabharath must have been actually produced by ants, if the size of the gold powder is any indication.
The interesting technique of granulation of gold in making jewelry was developed in Egypt and was used extensively by the ancient Greeks (ca 600 BC). Surface tension was used to turn melted gold filings into spheres. The granulation technique was also used to make gold jewelry in India in the late 1st millennium BC to early Christian era. Interestingly, as far as silver production goes, the Aravalli region in north-west India along with Laurion in Greece and the Roman mines of Rio Tinto in Spain ranks amongst the few major ancient silver producing sites from about the mid 1st millennium BC onwards.
The earliest firm evidence for the production of metallic zinc is from India. Of the metals used in antiquity zinc is one of the most difficult to smelt since zinc volatalises at about the same temperature of around 1000oC that is needed to smelt zinc ore. As a result it would form as a vapour in the furnace which would immediately get reoxidised and hence lost. Hence metallic zinc is seldom reported in antiquity. However in India there is unique evidence for the extensive and semi-industrial production of metallic zinc at the Zawar area of Rajasthan. An ingenious method was devised of downward distillation of the zinc vapour formed after smelting zinc ore using specifically designed retorts with condensers and furnaces, so that the smelted zinc vapour could be drastically cooled down to get a melt that could solidify to zinc metal. The Rasaratnakara, a text ascribed to the great Indian scientist Nagarjuna, of the early Christian era describes this method of production of zinc.
In Europe, the production of metallic zinc was virtually unknown until William Champion first established commercial zinc smelting operations in Bristol in the 1740’s following which it was industrially produced. Interestingly the method of production adopted by downward distillation bears a strong resemblance to the Zawar process and it has been pointed out that Champion’s process was very likely inspired by the Zawar process which would have been made known to the British during the forays of the East India Company.
Another remarkable artistic innovation by Indian metalworkers of the past was the use of zinc in making highly elegant bidri ware, an inlayed zinc alloy, which came into vogue under the Muslim rulers of the Bidar province in the Hyderabad region from about the 14th century. AD. Several impressive vessels, ewers, pitchers, vessels, huqqa bases etc. were made of bidri ware with patterns influenced by the fine geometric and floral patterns and inlayed metal work of the Islamic world where decorative metalwork reached some its most exquisite heights, for instance in the metalwork of the Ottoman empire.
Iron occurs in the native metal state as meteoric iron which was exploited by the North American Indians to make weapons. Since iron has a high melting point of around 1550oC it was commonly produced in the Old World by reducing the ore to metal in the solid state to produce bloomery iron which was then wrought to give low carbon wrought iron (0.1-0.2 % C). The Hittite kingdom of the mid second millennium BC was one of the major early iron producing centers and was thought to have a monopoly of iron production, and iron production became widespread in Greece and the Mediterranean by the beginning of the 1st millennium BC. Iron seems to have been used in India from about the late second millennium BC and iron smelting and the use of iron was especially well established in the south Indian megalithic cultures of this period.
The forging of wrought iron seems to have reached its zenith in India in the first millennium AD. The earliest large forging is the famous iron pillar at New Delhi dated by inscription to the Gupta period of the 3rd c. AD at a height of over 7 m and weight of about 6 tons. The pillar is believed to have been made by forging together a series of disc-shaped iron blooms. Apart from the dimensions another remarkable aspect of the iron pillar is the absence of corrosion which has been linked to the composition, the high purity of the wrought iron and the phosphorus content and the distribution of slag.
In fact the use of high-carbon iron alloys was developed in parts of Asia before they came into vogue in Europe. We may mention high-carbon steel from India and cast iron from China, both of which required higher furnace temperatures and more reducing conditions than the bloomery iron process. Cast iron was produced in China prior to other parts of the world in small blast furnaces which were precursors to the modern blast furnaces. Cast iron with a high carbon content of between 2-4% C is a brittle and fairly unworkable alloy with poor strength, but it has the lowest melting point in the iron-carbon system being a eutectic at around 1100oC. By the early Christian era in China cast iron was used on a very large scale for producing tools, weapons, vessels and utensils.
In Europe the use of cast iron was not appreciated until after about the 14th c. AD when it was used for making cannons. By the end of the 18th century cast iron began to be used extensively in England in building and construction. The famous Mysore Palace in Mysore near Bangalore built by the Wodeyars at the turn of the century was the first royal palace in India to make use of cast iron in architectural construction.
India has been reputed for its iron and steel since Greek and Roman times with the earliest reported finds of high-carbon steels in the world coming from the early Christian era, while Greek accounts report the manufacture of steel in India by the crucible process. Wootz is the anglicized version of ukku in the languages of the states of Karnataka, and Andhra Pradesh, a term denoting steel. Literary accounts suggest that steel from the southern part of the Indian subcontinent was exported to Europe, China, the Arab world and the Middle East. In the 12th century the Arab Idrisi says ‘The Hindus excel in the manufacture of iron. It is impossible to find anything to surpass the edge from Indian steel’.
Studies on Wootz indicate that it was an ultra-high carbon steel with between 1-2% carbon and was believed to have been used to fashion Damascus blades with a watered steel pattern (Srinivasan and Griffiths 1997). Experimental reconstructions by Wadsworth and Sherby in the 1980’s have demonstrated that ultra-high carbon steels with about 1.5% C can be used to simulate ‘Damascus’ blades and that these exhibit fascinating superplastic properties. Superplasticity is a remarkable phenomenon which allows a material to change its external shape to a very great extent without changing within.
A description from the Crusades of the Damascus blades is as follows: ‘One blow of a Damascus sword would cleave a European helmet without turning the edge or cut through a silk handkerchief drawn across it’. One sixth century writer describes blades as having a water pattern whose ‘wavy streaks are glistening-it is like a pond on whose surface the wind is gliding’.
Wootz steel also played an important role in the development of metallurgy. Michael Faraday, the greatest experimenter of all times, tried to duplicate the steel by alloying iron with a variety of metallic additions including noble metals but failed. As he was the son of a blacksmith the extraordinary properties of Wootz steel must have fascinated him. His failure had an unexpected and fortunate outcome as it marked the beginning of alloy steel making. Wootz has been a prime motivating force in the development of metallurgical science and the study of micro-structures. Although iron and steel had been used for thousands of years the role of carbon in steel as the dominant element was found only in 1774 by Tobern Bergman and was due to the efforts of Europeans to unravel the mysteries of Wootz. Similarly the textured Damascus steel was one of the earliest materials to be examined by the microscope. British, French and Russian metallography developed largely due to the quest to document this structure. Wootz was an ‘advanced material’ of the ancient world used in three continents for well over a millennium. Neither its geographic sway nor its historic dominance is likely to be equalled by advanced materials of our era.
Mercury is a metal that has been of great alchemical importance in ancient times. In ancient China there is evidence that mercury was used by the latter half of the first millennium BC mercury while mercury metal is reported from Hellenistic Greece. Mercury is a volatile metal which is easily produced by heating cinnabar followed by downward distillation of the mercury vapour. Some of the earliest literary references to the use of mercury distillation comes from Indian treatises such as the Arthashastra of Kautilya dating from the late first millennium BC onwards. Some evidence for mercury distillation is reported from the ancient Roman world.
In India, vermilion or cinnabar i.e. mercuric sulphide has had great ritual significance, typically having been used to make the red bindi or dot on the forehead usually associated with Hinduism. Ingeniously in ancient Chinese tombs cinnabar was used successfully as a preservative to keep fine silks intact. Mercury was also at the heart many alchemical transmutation experiments in the Middle Ages in Europe as well as in Indian alchemical texts which were precursors to the development of chemistry.
In ancient Predynastic Egypt (ca 4000-3000 BC) galena or lead sulphide was used in the manufacture of kohl or eyeliner and indeed a striking feature of Egyptian art is the beautiful and exaggerated lining of the eyes. Stone palettes for grinding kohl are found in ancient Egypt along with artifacts of lead indicating that lead was one of the earliest metals to be smelted since lead ore is easily reduced and does not require very high temperatures. Lead was commonly alloyed with copper and bronze for making castings. In De Re Metallica, a Renaissance period text authored by Agricola more than five centuries ago, the Westphalian process of smelting lead ore is described where lead ore is smelted in an open hearth. The mineral-rich Aravalli region of Rajasthan was one of the important early lead mining regions in antiquity. The use of low melting lead-tin eutectic as a solder became common in Europe by the late medieval period.
Native copper, i.e. copper metal, is thought to have been the first metal used by man and may have used in ancient Turkey and Mesopotamia by about the seventh millennium BC. Native copper is abundantly available in large masses in the Great Lakes region of North America and was used fairly extensively by the North American Indians to make weapons and implements solely by hammering and annealing so that casting and smelting was not attempted. Clear early evidence for smelting copper comes from the Middle East from about the fourth to third millennium BC onwards, from parts of Israel, Jordan and Egypt where copper oxide ores such as green malachite were smelted at temperatures of around 1200oC.
Early copper artifacts of about the sixth millennium BC are also reported from the pre-Indus Valley sites of Baluchistan in the northwestern part of the Indian subcontinent close to the Iranian border. There is also some evidence for smelting furnaces from the Harappan civilizations of the northwestern part of the Indian subcontinent. There is fairly extensive evidence for the ancient mining of copper ores from the Khetri region of Rajasthan in northwestern India dating to about the 3rd-2nd millennium BC.
Arsenical copper was also in use in Mesopotamia, prior to the use of tin bronzes, of which the most famous and extraordinary examples are the bronze bulls of the third millennium BC where the enrichment of arsenic at the surface is found to give it a shiny coating.
Tin ore occurs as alluvial deposits as well as ore bodies. One of the most extensive tin mining regions in the past was Cornwall in Britain which is thought to have been mined at least by Roman times while Southeast Asia has some of the largest alluvial tin deposits. Tin was alloyed to copper to get harder bronze for making weapons, prior to the use of iron, in the Bronze Age cultures of the world. Tin mines are known from ancient Turkey dating to the third millennium BC.
Amongst the earliest bronze castings in the world is the well executed statue of a dancing girl from Mohenjodaro from the Indus Valley, while beautiful bronzes are also known from ancient Egypt such as the famous cat which are thought to have been executed by the lost wax technique. In China very impressive ceremonial vessels were cast into clay moulds by the late second millennium BC to early first millennium BC. The Greek bronze figurines of the first millennium BC are well known. Some of the most beautiful and well executed bronze castings in the world are the icons from the Chola period in the Tanjavur area of south India (ca 10th c. AD). South Indian bronzes were mostly solid cast whereas images from Southeast Asia are mostly hollow cast. Mirrors were made of bronze in different part of old world including India. Investigations by Srinivasan show that that the earliest and continuing use of artifacts of rapidly quenched high-tin bronzes is from the Indian subcontinent.
The above review indicates that there is growing evidence to suggest that ancient Indian metallurgists have also made major contributions which deserve their place in the metallurgical history of the world along with other great civilizations of the world. As clearly seen in the case of zinc and high-carbon steel, ancient India contributed significantly to their modern metallurgical advances and in the development of metallurgical study leading to the Industrial Revolution in Europe and hence deserve a special niche in the annals of western science. In this Golden Jubilee year of the department it is worth recalling the achievements of the past as a source of inspiration and confidence for future generation of metallurgists in India and elsewhere. Prof. Cyril Stanley Smith has remarked that usually man assays metals. Metal can just as well be used to assay the progress of mankind. In this assay the ancient civilisation of India acquits itself with glory.
The authors would like to thank the Indian National Academy of Engineering (INAE) and one of the authors (SS) would like to thank the Homi Bhabha Fellowships Council for their support and British Council, New Delhi for support to the Phd. research at University College London.
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