Microchemical investigation of archaeological copper-based artefacts used for currency in ancient Italy before the coinage

By means of the combined use of XPS and scanning electron microscopy + energy dispersive spectrometry (SEM + EDS), the microchemical structure of long-term corrosion products grown on Aes Rude, i.e. archaeological unworked lumps of Cu-based materials, has been carried out. In ancient Italy, these materials have been used as currency, as a medium of exchange and as a form of saving, from the sixth to the third centuries BC before the use of the struck metallic coins. The results of the microchemical investigation disclose their apparently unusable nature for any functional applications or possible use, being constituted of highly ferruginous leaded copper, and demonstrate that Aes Rude were a primitive form of currency as suggested by archaeologists. Furthermore, XPS and SEM + EDS results give evidence on the corroded external region of the presence of Cu (II) hydrates mixed with hydrated iron oxide and aluminium-silicon phases coming from the soil that have been incorporated into the patina. This information is useful to identify the material nature of these archaeological artefacts and to select tailored conservation strategies finalized to ensure long life to these relevant ancient materials.