Making the Dies and Coin Blanks

Dies in Classical times were made of bronze, steel, and iron (Zograph 1977: 45). However, most of the ones that survive today are made of bronze since iron corrodes completely (Sellwood 1976: 69). Because bronze dies were made of high-tin bronze and were brittle and easy to shatter, I chose to make the dies for my experiment out of low-carbon steel, comparable to the iron dies the Romans used.

For the upper die, I cut a five-inch rod of one-inch diameter. For the lower die, I cut a one-inch rod of one-inch diameter. Next, I penciled in the designs onto the dies and then painstakingly carved the designs using hand gravers (Figures 2, 3, 4, 5, 6). The obverse, which depicted a head, took about twenty hours, the reverse, a comet, took only four. I made only one pair of dies due to time constraints and to maintain consistency. If I made two pairs of dies to recreate the actual appearance of the emperors from the two different time periods, each would have slightly different depths. This difference may be an unwanted factor in the experiment because deeper impressions may be more work-intensive than shallower ones.

I replicated the coin blanks through a method described by Beer (1982) and Zograph (1977). Zograph said, “For gold and silver coins which required this precision …The precious metal, in the form of grains of granules to the amount required for a given coin, was weighed out on a balance and was put in a refractory crucible which was then placed in the melting furnace, where the grains ran together into a single pellet” (Zograph 1977: 36). The surface tension of liquid metal automatically pulls together the granules into a single pellet. In Beer’s (1982) experiments on minting ancient Aegina turtle coins, she measured the desired weight in silver granules. She then used a blowtorch to melt the granules in a depression in a charcoal block. This formed a silver pellet (Beer 1982: 49). Because charcoal creates a reducing atmosphere, oxidation would be kept at a minimum. Oxidation, which causes a discoloration of the coin, may happen with a clay mold. Overall, the decision to use a charcoal block or a refractory crucible should not affect the blanks produced.

At first, I did not want to melt each pellet individually using a blowtorch, because Beer (1982) described the process taking about five minutes for each. Instead, I weighed the granules (3.7 grams) and put them into multiple depressions in a charcoal block. I then put the whole charcoal block in a furnace, hoping to produce many pellets in a relatively short time. I tried this procedure with a charcoal block and enough granules to make two pellets, but it failed. Although the silver eventually melted into two nice pellets, the charcoal block became ashy and extremely fragile due to the prolonged exposure to intense heat in the furnace (Figure 7). Putting the charcoal block in the furnace was also not a good idea because it cracked the block in many places and this would have allowed silver to seep through the cracks. Because of the failure, I decided that I had no choice but to use a blowtorch.

To make the coin blanks of correct size, I followed Sellwood’s advice and hammered the pellets flat (Sellwood 1976: 66). First I melted the metal into a pellet and then I pounded the pellet with a hammer until it was the right diameter (20mm) (Figure 8, 9). My experimental design (see methodology below) required 120 blanks. I made an additional 60 blanks to practice on. In all, I spent about twenty-two hours making them.

The silver-copper blanks, 60% silver and 40% copper had extensive oxidation. I weighed 1.5 grams of copper and 2.2 grams of silver and combined the two quantities for melting. The oxidation was removed in the Roman times by quenching the hot blank in some sort of acid (Clay 1988: 347). This rids the coin of oxidation and also leeches away some of the copper on the surface, giving the alloyed coin a more silvery appearance (Figure 10). However, the copper-tone is still obvious. It takes about 7 to 8 minutes to melt and hammer out one silver-copper blank because of the hardness of the alloy.

The silver blanks had little or no oxidation (Figure 11). It only takes 3 to 4 minutes to make a silver blank (3.7 grams) because it is relatively soft. However, because of its softness, these coin blanks had a much higher occurrence of stress fractures compared to the silver-copper alloy blanks (Figure 12). These stress fractures are seen in many Roman coins. I tried to reduce the stress fractures by experimenting with hammering the pellets while hot and while cold. In both cases, the stress fractures still resulted. Contrary to what Sayles said (Sayles 1998: 131), stress fractures have no relationship to whether the pellet was hot or cold struck. Rather, the stress caused by the hammer blows seems to exploit the weaknesses in the structure of the pellet. Instead, I noticed that the more thoroughly melted the pellet was, and thus the more uniform the structure of the metal, the less likely there were going to be stress fractures. This was the same for silver-copper pellets. Table 1 is a summary of the time it took to do each of the tasks described.