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Copper in Ancient India c12.s2: Metallurgy of Copper

Copper in Ancient India c12.s2

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English

Metallurgy of Copper

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A connected history of the metallurgical operations used in the extraction of copper is extremely difficult to make out, as the description of the processes of extraction of copper is extremely meagre in alchemical literature. It has already been pointed out that copper pyrites and copper glance were the two copper ores commonly mentioned in alchemical works and recipes have been given in these works for the extraction of copper from these ores. No furnaces, however, are described, the operations being conducted in crucibles. A few such recipes for the extraction of copper from *mākshika* and *Vimala* are given below:

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(1) *Mākshika* or pyrites—the following recipe is given in both *Rasārnava* and *Rasaratna-samuchchaya*: “*Mākshika*, repeatedly steeped in honey, oil of the seeds of *ricinus communis*, urine of the cow, clarified butter and the extract of the bulbous root of *musa sapieutum* when gently roasted in a crucible yields an essence in the shape of copper.”¹

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¹ ज्ञोट्रन्वर्व्वतत्वाभ्यां नोमूत्रेण पृतेन च । कदलोकन्नधमारेण भावितं मासिकं मुडः । नूवायी मुक्षति धातें सत्त्वं शुलनिनयं मृदु ॥ Rasārnava, VI, 12—13. Rasaratna-samuchchaya, II, 89—90.

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(2) *Vimala* or copper glance—the following formula for the extraction of copper from *Vimala* is given in *Rasaratnākar*, *Rasārnava* and *Rasaratna-samuchchaya*: “*Vimala* digested with alum, green vitriol, borax and the watery liquid extracted from *moringapter*, *musa sapientum* and finally roasted in a covered crucible in combination with the ashes of *schrebera swiet*, yields an essence in the shape of *chandrārka* (literally copper of gold-like lustre).”²

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² विमलं शियुतीयेन काङ्कोकासीशटंकणैः । वज्रकन्दसमानुप्तं भावितंकदलीरसैः ॥ मोज्झकवारसंयुक्तं ध्मामितं मूकभूवगम् । सत्त्वं चन्द्राकसंकायं प्रयछतिन मशय ॥ Rasaratna-samuchchaya, II, 103—4.

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Another formula for extracting copper from *Vimala*, is found in *Rasaratna-samuchchaya*: “*Vimala*, rubbed with borax, the juice of *atrocarpus lakoocha* and the ash of *schrebera swiet* when roasted in a covered crucible yields an essence of the appearance of gold.”³

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³ सटङ्कणकुट्ठावयपश्वङ्गच असना । पिटा सूवोटरे लिङ्गः संशोष च मिरुष्य च ॥ पट्प्रख्यकीकि नैर्द्धतो विमलः शीतसन्नभः । सत्त्वं गमति तद्युक्को रसः व्यात् स रसायनः ॥ Ibid, II, 101—2. The translation of the passages is as given in Ray’s History of Hindu Chemistry, Vol. I, p. 46 and 47.

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The chemical action that takes place in the processes given in the formulae mentioned above for the extraction of copper from its ores in covered crucibles is apt to be lost in the wilderness of names of various plants which evidently supply the carbon by destructive distillation when heated in covered crucibles. The carbon, borax and the alkali carbonates supply the reducing agents for the conversion of the ores into metallic copper.

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It would be difficult to say whether such processes as described above were actually used on a large scale for manufacturing purposes in copper mines, though it is evident that they were used as laboratory methods on a small scale as covered crucibles are mentioned. From the existing archaeological and mineralogical evidences elaborated in previous chapters it is evident that copper was extracted in India from their ores in sufficiently large quantities from the third century B.C. when the Asoka pillar copper bolt was manufactured down to the Moghul period when large brass guns were cast, and that for that purpose the extraction must have taken place in big furnaces and not in small crucibles. Unfortunately literature on this subject has all perished by the ravages of time, and exact descriptions of the furnaces employed as well as of the metallurgical processes themselves are wanting at this great distance of time. Fortunately, however, copper smelting is still carried on in different parts of India, as has been already mentioned, in Khetri, Singhana and other places in Rajputana and in Nepal and Sikkim Himalayas, and judging from the conservatism of the people it is to be presumed that the industry was carried on for many centuries in a like manner though certainly not on such a poor scale. It has already been pointed out that the scientific and industrial spirit has been waning in India from the 12th or the 13th century, and by the middle of the 16th century the emasculation of the spirit of industry and inquiry has become almost complete owing to decadent national vitality, and most industries have in consequence gradually been relegated by that time into the hands of the illiterate and the least advanced sections of the Indian community. The metallurgical skill displayed by the ancient Indians in the forging of the gigantic iron pillars of Delhi and other places, the iron beams of Konarak, Puri and Bhubaneswar was certainly of very superior order, but descriptions of the furnaces, which were certainly of no mean dimensions, used in forging these beams and pillars and of the actual process of the extraction of iron, which must have been effected in very large quantities, have been lost in the obscurity of the distant past. Old processes, however, both of copper and iron smelting still continue, though on an infinitely smaller scale, amongst the aboriginal and the least advanced communities of India. These processes are important as relics of a bygone industry which produced in the past articles of value which still attract the unstinted admiration of competent judges and experts.

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We would therefore conclude by giving short descriptions of these indigenous processes of manufacturing copper as they existed about three quarters of a century ago and in fact are still existing in India in Rajputana, Nepal and other places :—

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Rajputana—Capt. Boileau in his “Gleanings in Science (Vo. III, p. 380) gives a description of the native process of manufacturing copper in Singhana as it existed in 1831 and Col. J. C. Brooke in 1864 gives an account of the same process in Khetri with diagrams and plates.¹ Their accounts may be summarised thus :—The principal ores in Singhāna and Khetri were copper pyrites. They were pounded with hammers weighing 16 to 20 lbs. on stone anvils. The crushed ores were then mixed with cow-dung, made into balls and dried in the sun. The ores were first roasted and then mixed with charcoal and iron slag as flux. There are hillocks of iron slag in these places showing that iron was also smelted here at one time in very large quantities. The furnace was made by piling on one another three or four concentric clay or fire clay cylinders with arrangement at the bottom for two nozzles of two ordinary hand bellows used for driving a blast of air. The height of a furnace would not exceed 30 or 40 inches and its external diameter 15.

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¹ Col. J.C. Brooke, Journal Asiatic Soc., Beng., Vol. xxxiii, pages 519—529. For a fuller description of furnaces and process consult Percy's Metallurgy p. 390 and Ball's Economic Geology of India, p. 260.

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inches. During a day of nine or ten hours 3 maunds charcoal, 2½ mds, roasted ore and 2 mds, iron slag were consumed. The slag was drawn off and the molten copper remained at the bottom and removed next day. It was then re-melted in an open furnace under a strong blast of air and then cast into ingots of refined copper.

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*Sikkim Himalayas*—The description of copper manufacture in Sikkim Himalayas given by Mr. H. F. Blanford of the Geological Survey of India and quoted in Percy's Metallurgy published in 1861 does not differ materially from the description given by Col. Boilean and Col. Brooke of the Rajputana copper works. The workmen are all Nepalese who, as references in alchemical works already quoted show, were adepts in copper manufacture. Mr. Blanford's observations may be summarised thus:—

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The ores are picked, crushed, powdered, subjected to several washings and then become ready for preliminary smelting. The washed ore consists of copper pyrites, mundic and gangue principally quartz and hornblened. The furnace is formed of refractory clay and is in the form of a truncated pyramid. It is generally 18 inches deep and there are arrangements at the bottom for a blast of air with two bellows consisting of inflated goat skin.

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*Smelting*—The furnace is filled with lighted charcoal which is raised to its full heat and the washed ore thrown in the furnace. The bellows are worked by hand until the fused "regulus" forms a small pool at the bottom covered with a layer of fused slag. The crude metal is removed when cooled.

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*Roaxling*—The crude metal is then kneaded with cow-dung into small balls, dried in the sun and roasted in a shallow furnace formed of a ring of slag cakes placed on edge.

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*Refining*—The roasted metal is afterwards refined in the first furnace, charcoal completely reducing the metal. The refined copper is collected at the bottom and removed as cakes when cooled weighing four or five pounds.

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The traditional Indian method of the extraction of copper is akin in principle to the modern blast furnace method of smelting copper first described by Agricola in the middle of the sixteenth century whilst writing about the working of the Mansfield copper works. The Mansfield process has been perfected by Herreshoff and others and the chemistry of the modern process is almost identical with that of the traditional Indian method. For the sake of comparison the principle of the modern method is being quoted below—"the roasted ore, mixed with coke or anthracite, and the slag from a later process, which consists chiefly of iron silicate with a little copper, is introduced at the top of the furnace, the air being forced through fuyeres. The products, which consist of 'matte' and slag accumulate in the bottom of the funace and then overflow continuously into the 'fore-hearth'. This matte is usually reduced to metallic copper in a 'converter', the resulting metal being refined in reverberatory furnaces."¹

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¹ Roscoe and Scholemmer, *Treatise on Chemistry*, Vol. II, p. 499.

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It would thus appear that the old Welsh or English process of copper smelting in reverberatory furnaces which requires a very large number of calcination and roasting had no counterpart in India, the Indian process being conducted in blast furnaces.

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