History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c14.s3: IV

History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c14.s3

Language: English

IV

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These difficulties faced in producing casts or repoussé coins could have been obviated by following another technique of minting. We are referring to the system of producing coins with the help of well prepared blanks and dies (each of which, meant to be impressed, with the exclusion of others, on obverse or reverse, bears a cohesive picture of devices related to one another or such devices and legends or only a meaningful legend or a part of it). This system was, at least in the early centuries of its use, a sophisticated development on the above noted archaic die-striking (including ‘punch-marking ’) methods.

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Among the most well produced die-struck series of specie of Ancient India we can include the coins (or at least many pieces) issued by the Indo-Greeks, Schtho-Parthians, Kuṣāṇas and Imperial Guptas. The appearance of two distinct devices or rather two distinct sets of cohesive devices of their coins and traces of double striking on blurred faces of some of these pieces suggest that the coins of these rulers were struck from two separate dies, used probably simultaneously. The method of die- struck coins of the Gupta and Pre-Gupta periods consisted mainly of gold, or silver, or copper or lead or billon (an alloy of silver with copper or tin), or potin (a compound of copper, lead, zinc and tin)⁹.

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The exact process of extraction (or segregation) of crude metal from native metal deposits and also the exact process of purification or refining of crude metal varied from metal to metal, as suggested by mediaeval and modern experience. However, a few early and mediaeval treatises perhaps indicate that firing of the metal was an essential part of each method (Dravyaparīkṣā, 17ff; Āīn-i-Akbarī, 6,3-9; 10-14; Viccaji; Ray, 1956, p.209 vide Parrington, 1961 pp. 716ff; Arthaśāstra IV, 4, 20; 11,13, 9 and 49).

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‘Purified’ remains of gold, copper, silver, etc., could have been melted and cast into ingots. “Mixed” metal like billon or potin could have been prepared by mixing prescribed quantities of molten metals and then casting the materials into ingots. These ingots supplied the basic materials for preparing blanks.

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It appears that the required amount of basic material was first melted down. The molten metal could have been mixed with prescribed quantities of alloying materials (whenever necessary), as in the case of preparing gold or silver coins.

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Then the required amounts of molten metal were probably poured into circular shaped moulds of regulated sizes.¹⁰ The blanks produced for the moulds could be heated and worked upon by hammering, etc., for achieving the required thickness and for destroying the brittle cast structure of their grains and thereby making them conducive to receiving the blow at the time of striking. Alternatively, the molten metal (mixed with alloying material) could have been cast into sheets or plates, which could be heated and worked upon and finally cut into round pieces of the size of the coined money.

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After preparation of blanks their weight might have been checked and adjusted according to the specified standard. We do not know whether, as in several manually operated mints of medieval and early modern times, the blanks were blanched by boiling them in a solution (like that of tamarind and salt) in order to clean and perhaps also to soften them.

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Preparation of dies was another important stage in production of coins. Impressions in relief on most of the well produced die- struck pieces suggest that devices on the relevant dies were hollowed out. We can guess two, if not more, possible ways for preparing these “intaglio” dies.

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Negative impressions of the obverse and reverse types (and inscriptions) could have been engraved, perhaps following an original design, on two separate dies of soft steel or bronze, prepared by cutting into slices a bar of steel or bronze, cast in mould and then annealed (i.e. softened by heating the bar to a temperature somewhat below the melting point and then allowing it to cool slowly)¹¹. The engraving might have been done by a sculptor with the help of such instruments as a graver’s wheel, drills of different shapes and sizes, a burin, a hammer and perhaps a compass.

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We can consider an alternative and perhaps a more practical or an easier way of making dies. The sculptor could have engraved in positive the obverse or reverse design on a lump of specially prepared plastic clay containing aluminium silicate and so possessing high heat-resisting capacity and high softening point (PCE).

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The lump of clay displaying the design would have to be fired properly. Then the terra-cotta design or model could be covered by molten ingredients of steel or bronze for transferring the design in negative on the gradually hardened material¹².

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Increased hardness could be achieved in case of a metal die, prepared following the first or second process, by heating it to a temperature somewhat below the melting point and cooling it by water quenching.

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The obverse and reverse dies were now fit to be used in a mint. One of them was fixed on or embedded in an anvil. The other die was attached to (or engraved on ?) a (square or an oblong shaped?) punch.

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Each metal blank was heated or was slightly softened by annealing (to make its hard material ready to receive the required impressions) or was left cold. The blank was then set on the die fixed on the anvil and the die-end punch was placed on it (i.e. the blank).

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The fact that the reverse type on numerous die-struck coins is found double-struck and/or partly out of flan does not at least indicate a regular use of any mechanical instrument (like a hinge connecting the two dies)¹³ to keep the upper die in proper place during the time of minting. Nevertheless, a regular alignment of the obverse and reverse impressions on a great number of coins suggests that care was at least sometimes taken before striking to put the upper and lower devices parallel to each other.

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The actual striking seems to have been done with the help of a hammer. After placing the die-end of the punch on the cold, or annealed or incandescent blank already set between the anvil-die and the punch-die the other end of the punch was struck with a hammer. As a result both sides of the blank received the required impressions and it was transformed into a coin. A recent experiment in Greek minting technique reveals that two blows of the hammer were sufficient to give full impression of both the dies on the flan (NC, 1963, p.226).

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Several coins, scrutinised under microscope, show homogeneity or near-homogeneity in size of the grains of their metal.¹⁴ This indicates that even if the coin was cold worked, the cast metal of the blank was heated and worked out (as indicated above). Or we may presume that a cold worked coin was heated to a high temperature to remove the strain sustained by its metal at the time of striking. At the time of heat treatment a good amount of recrystallisation could have taken place making the metal quite homogenized from the point of view of size of its grains. The same effect could have been achieved by striking the blank at a high temperature. But the hot-working could have affected the die-life.

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An examination of a large number of coins apparently intended to be round reveals that only a few of them are exactly circular in shape. It appears that the very method of production followed in ancient Indian mints made it impossible for the true circle to be obtained, since there was nothing to stop the flan from spreading irregularly under the blow of the hammer.¹⁵

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Unutilised space around the full impression of a reverse device can be noticed on a number of coins. This indicates that in these case the punch-die or the upper die was smaller than the blank set on and covering the face of the anvil-dies.

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The use of smaller upper die may have originated from the desire for allowing the blank to have enough space to receive the full impression of the reverse device even if there was some oscillation of the punch-die during the time of manually operated production. We should also note that the available evidence in other fields of numismatic research shows that an upper die (trussel die) was less durable than the lower die (pile die). So in a given period a mint might require more upper dies than lower dies. Hence the smaller size of the punch-die could have lowered the cost of production in a given period which would have been otherwise grater then the amount required for manufacturing the anvil-dies. As a result of hard striking by the smaller upper die on the blank its outer marginal part outside the area stamped with the relevant device became a little raised. Such concave reverse may be noticed on some coins, which have convex obverse (Mukherjee, 1967, Pl VI A, No. 9; Pl. VIII A; No.21; JNSI, 1956, Vol.XVIII; Pl 1, No.2f).

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Defects of various types, as noted above, are, however, not noticeable on a large number of coins of the pre-Gupta and Gupta ages including numerous Indo-Greek, Kusana and Gupta pieces. Many of these can be classed as objects of art. (Mukherjee 1978, pp.16ff; 1982, pp.20ff; 1983, Vol. XVII pp.22 ff). Production of such quality die-struck coins depended on the artistry of the obverse and reverse devices, excellence of the relevant die(s), purity and/or suitability of the required metal, efficiency in technique of minting and will and resources of the minting authorities (Mukherjee, 1982, pp.10 and 64).

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The majority or even all of these conditions remained unfulfilled by the strikers of the greater number of series of specie in the post-Gupta age, when a large number of ruling families did not at all strike coins (Mukherjee, 1982, p.66, n.2) We even do not know of coins of all members of all the ruling families of this age, who are credited to have their own coinage.¹⁶ There are reasons to believe that coins were used to be minted by rulers of at least certain dynasties only when there was demand for them in market and then also new pieces were struck often with old familiar types (Mukherjee, 1982, pp. 66-67, n.3) and sometimes even with the names of dead rulers (whose coins had already become popular with the people). Private moneyers were also allowed to mint coins. They were understandably not at all keen to maintain the quality of coins and purity of metal. As a result, coins bearing the name of a ruler might have continued even after his death, to be imitated in gradually debased metal and technique (Mukherjee, 1982, pp. 49ff).

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¹⁶ *Valdettaro (JNSI,35, Pl.1. no.13, 1973) and, following him, A.N. Lahiri, calls the pieces in question as “droplet” coins (JNSI, 1976, vol.XXXVIII, p.4). The word “droplet” means “a little drop”. But a blank of this type of coins might have been produced by a large drop or several small drops of metal. So it is

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This situation explains the hopelessly debased materials used in minting several series of die-struck specie in post-Gupta India (Mukherjee, 1982,pp. 39,41, 43, 49 etc). On many coins the figures are ill-executed and even grotesque, obviously due (partly or fully) to deficiency (a) in the merit of the designer, and/or die engraver (or designer-cum-die-engraver), and (b) in the metal of the die, and also (c) in the technique of minting.

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. On a fairly large number of coins an emphasis on delineating only the outlines of the figures in high relief is noticeable. This technique of execution was probably necessitated due to use of poor and alloyed metal and of dies deeply sunk in the relevant places only (Mukherjee, 1982, pp.43 and 53).

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Economic and political factors led to deterioration in the system of coinage, affecting seriously its typological, metrological, and technological aspects. The situation was quite chaotic when the power of Islam became firmly established as the most dominant political authority in the subcontinent in the 13th century A.D. However the conditions of minting became, to some extent, improved in the next few centuries, particularly in the age of the early Great Mughals.¹⁷

Linked texts (1)

Kauṭilīya Arthaśāstra — Kauṭilya, Sanskrit