Archaeometallurgical characterisation of ancient Roman bronze coins

Abstract

Introduction: The three of several ancient bronze coins were selected for this master thesis research. The coins were considered to belong to the Roman mint of the Egyptian origin in the province of Alexandria. They were excavated in the archaeological site Bubastis ancient city. Archaeometallurgical characterisation of those coins implies to a performance of detailed investigation of the chemical composition and microstructure of the alloy and the analysis of corrosion products of the coins. The archaeometry analysis was performed by means of a multi-analytical approach: X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) will be used to determine the elemental composition and microstructure of the bulk metal and understanding the corrosion mechanism. The origin of the three ancient bronze coins that were chosen for performing the present master thesis research is not known for sure. They are a part of a several coins collection that were purchased at a market in Egypt in Cairo with a purpose of their material study in sense of advantages of conservation science and archaeometry. It is known that nowadays it is not easy to acquire samples of historical value to perform a scientific research, taking in consideration the situation with some museums laws, that sometimes or usually do not support an idea of cooperation between cultural heritage protection and conservation science. On the other hand, a research on material study in most usual cases requires destructive methods of analysis by application of some analytical techniques that consider sample preparation (like cross-sections). ‘It is often difficult to persuade museum curators to permit any sampling technique that involves the physical removal of metal from a coin, although all relevant techniques require the removal of at least some material in order to obtain or expose the ‘heart metal’ of the coin…’ 1 [1] Obviously, the chance of destruction of cultural heritage object is not in any case acceptable, which is one of the reasons of absence of contact between museums and archaeometry and conservation science. In this case, it was necessary to find other ways of obtaining the samples, and the simple idea of their purchase was quite essential.