Experimental analysis of Roman coin minting

Highlights

• New experimental routine for the analysis of historic coin minting

• Detailed description of the procedure and evaluation method

• Focus on the question of “hot”, “warm” or “cold” striking of coins

• Application of the approach on Roman coins

Abstract

Historic coins are an artifact used for analysis in different research areas. This study contributes to the topic of historic coin minting. Consulting ideas from the field of experimental numismatics, an approach is proposed to evaluate minting of certain coins supported by real test samples. Therefore, a test setup is implemented for the manufacturing of coins under controlled process conditions. In this work, the main focus lies on the coin blank temperature used for striking and thus, to contribute to the controversial problem, if minting is done “cold”, “warm” or “hot”. In order to prevent confusion, a suitable definition of the terms “cold”, “warm” or “hot” with respect to the materials recrystallization temperature is given. Various test samples of copper-based material are manufactured for different process conditions and initial coin blank temperatures, ranging from ambient temperature to 900 °C. Roman coins values, Dupondii and late Roman AE coins, are conducted for a comparative analysis. All coins are evaluated and compared based on metallographic micro-sections. On the basis of the conducted test, strong indications are found for a “hot” striking process.

Introduction

In the Roman Empire, basically, three different coin value classes can be differentiated: gold coins, silver coins and coins from Aes, which in ancient Rome represents a collective term for copper, bronze and brass (Blümner, 1886, Moesta and Franke, 1995, Klein et al., 2004, Kraft, 2005, Butcher et al., 2015). At this time, the value of a coin is controlled by its material (Metcalf, 2012). Asses and Folles, for example, which are usually made of pure copper or bronze have a lower value compared to silver, gold or even brass coins, such as a Dupondius or Sestertius. This is due to the then relatively high tin and zinc prices (Moesta and Franke, 1995).

Coinage has existed for over 2000 years and, since then, the goals have remained the same. The minted coins should be forgery-proof, wear-resistant and identical to each other (Howgego, 2013). In this context, the manufacturing process is of high importance. The processing of coins is one of the first examples for mass production, however, only its basic principles have remained the same (Moesta and Franke, 1995, Vontobe et al., 2005). Nowadays, coins are being produced in automated plants under ideal and constant conditions. In contrast, ancient coinage was based on handwork and manual operations. The coinage system played a crucial role in the progress of ancient Rome, since only under the prerequisite of a payment system, in contrast to the exchange system, a specialization of the population on specific tasks was possible (Evans, 2013). In this way, people were able to concentrate on particular fields of science, development and production (Kraft, 2005).

Up until now, the manufacturing process Romans used for the production of different coins is a controversial subject. Perhaps this is because the production of each coin material could be different. Therefore, a clear distinction between gold, silver, copper, bronze, brass and ore coins should be done, as performed for example by Butcher and Pointing (2005) for the Roman silver Denarius or Naismith (2014) for post-Roman gold coinage. Counterfeit money manufactured in a different way can also be a reason for different results. Further influences, like exposure to fire or mechanical loads make analysis rather difficult (Moesta and Franke, 1995). In particular, the minting procedure has not been adequately studied, to which this work contributes.

At this point the authors also would like to point out, that the focus of this work is to describe an experimental procedure for experimental numismatics. Hence, only brief information is given on the specific coins. The main part, and also field of expertise of the authors, is an extensive description of the testing setup and evaluation methods as a contribution to numismatics.