Most of the ancient dies that have survived are of bronze, although iron dies are thought to have been widely used also. Lower dies seem generally to have been disk-shaped so that they could sit in a recess on an anvil. In some instances the design may have been cut directly on the anvil. Engraving of the details was carried out using small steel tools (scorpers), or designs were drilled out using corundum dust. It is possible that major elements of the design were inserted by a âhub,â or master punch stamped into the die, but not all scholars accept that this method was employed in antiquity.
Blanks or planchets (i.e., the small metal disks from which coins are made) seem first to have been cast by pouring the molten alloy from a crucible onto a flat surface, where they cooled into the characteristic lens shape. Later the metal was poured into molds, which sometimes consisted of two parts so that the metal was completely enclosed; traces of the âflash,â or joining line, can still be seen on surviving coins. At Alexandria in the Ptolemaic period (323â30 bc), open molds were common; in these a sequence of disk-shaped impressions in the mold were connected by channels, and a number of blanks were thus obtained at one pouring. The upper surface of the blank, where slag and oxide accumulated, had to be âturnedâ off, or drilled out, presumably by a tool like a carpenterâs bit, and the centre punch mark to accommodate the tool point is characteristic of Ptolemaic, Seleucid, and Greek imperial coins. Contemporary issues in India were often square in outline and were cut by chisel from metal sheets. Many Greek and Roman silver coins were plated; an envelope of silver sheet was soldered on a copper core, and it is by no means certain that all such specimens were the work of counterfeiters, since solid silver and plated coins sometimes appear to have been struck from the same dies. In the later Roman Empire (3rd century ad) silver issues were heavily debased with copper; prior to striking, the blanks were immersed in an acid bath that leached out the surface copper to expose more silver, giving a much more acceptable appearance to the coins when they were first issued.
Strikingâthe impression of the die designs on the blanksâwas startlingly simple. The lower die, set in the anvil, was covered by the blank; the upper die, which was positioned above, was then given one or more hammer blows. A two-pound hammer, wielded by one hand, could easily give a force at the die face of seven tons. To get the high relief typical of Greek issues, two or three blows were necessary, and often there is evidence of double-striking on the coins. However, by preheating the blank, as practiced in Athens in the 5th century bc, less force was required and die life was extended. Analysis of the documentary evidence implies that one obverse (lower) die could produce upward of 20,000 coins, while 10,000 coins have been struck from a simulated bronze die without significant deterioration of the working surface. Receiving the hammer blows more directly, the reverse (upper) dies enjoyed about half the life of the obverse. Production rates varied. In small mints, operated by one man, a rate of 100 coins per hour has been shown to have been feasible. At important centres such as Rome or Antioch teams of four probably operated. An eyewitness account of a Persian mint in the 1870s describes how, with a hammerer, a die holder, a blank placer, and a coin remover, one piece could be struck about every two seconds.
Alterations in the flan (the coin disk, a term deriving from the French flatir, âto beat flatâ) led to corresponding changes in the manufacture of dies. In about ad 220 the SÄsÄnian dynasty of Iran introduced the concept of thin flan coins, issues that were struck in relief on both sides. In order not to produce intolerable stresses in the dies, since the thinner the material the more force necessary to make it flow into the recesses of the dieâs design, the depth of relief on such coins was of necessity much shallower than with earlier currency. Such techniques spread by way of Byzantium to northern Europe, where the emperor Charlemagne struck thin flan deniers (small silver coins), or pennies, which became characteristic of both his own and neighbouring kingdoms.
The Franks and Saxons inherited an art that was formalistic rather than realistic, and this permitted their coin designs to be made up from a small number of standard elements that were reproducible using punches. It has been shown, for example, that the complete dies for all of the coin types of Edward the Confessor of England could be obtained from seven punches, giving individual wedges, crescents, pellets, and bars, each of which was independently struck to make up a legend and design. Consequently, a single workshop could supply the 70 or so contemporary English mints in a relatively short time. An experimental pair of dies took less than an hour to fabricate. Of course, many European dies were produced by a combination of punching and engraving, while engraving alone was typical of early Islamic and contemporary Oriental dies. With the advent of larger denominations, such as the gros tournois (based on the weight standard of Tours, in France) in the 13th century, more florid designs came to be preferred, but the elements of the royal crown, for example, or the letters of the legend were still punched into the dies. To judge from surviving specimens, both upper and lower dies (trussells and piles) were by then produced from wrought iron. While the upper die retained the cylindrical shape of antiquity, the lower die was tanged (having protrusions added) so that it could be wedged into a wooden block.
The thin silver sheet required for the new coins needed to be beaten out from its cast state, and this in turn necessitated annealing (strengthening by slow cooling) to prevent cracking. By the 10th century, squares of sheet, somewhat larger than the eventual penny, were being struck between square dies and then separated by a circular cutter. A few imitative coins on square flans are known from Scandinavia, while die identical coins have exactly matching edge irregularities, proving use of the same cutter. With the introduction of the gros tournois, the blanks were cut roughly circular with shears, then gripped by special tongs in rouleaux (columnar rolls) of a dozen or more, and finally hammered into circularity on a flat anvil. Alternatively, the silver was cast into thin rods of rectangular section; pieces of the correct length (and hence weight) were next cut from the rod by chisel and then, with several annealings, were beaten to the appropriate thickness, before being rounded and struck by a die. Blanching (cleaning) of the blanks by an acid dip was necessary before striking to produce an acceptable surface if oxidation had occurred during annealing.
Striking was carried out in much the same way as during antiquity, although contemporary illustrations indicate that only one operator, not a team, was employed. Twelfth-century Byzantine coins were often cup shaped. A full impression of the curved dies could not easily be obtained by one blow; hence there evolved a method of striking one half of the coin with a slightly inclined upper die, which was then rocked over to the other side for a second blow. Bracteates, issues of foil thickness, were common in 12th-century Germany. To make these, a single die was used to strike a column of several blanks resting on a piece of leather, so that the reverse of each was the incuse (hollowed impression) of the obverse. Die life in general was higher than during antiquity, and documentary evidence for 13th-century English pence indicates perhaps 30,000 coins per obverse. There is no evidence for production rates.
