Study of archaeological lead artifacts from ancient Ostia (Rome) by mass spectrometry

This study is based on a systematic approach specifically focused on tesserae, tokens, seals, and other similar ancient lead objects conserved in the Depositi of Parco Archeologico di Ostia Antica (Italy). The primary goal of this work is to improve the knowledge about chronological and institutional framework of tokens (coinlike-objects) along with the development of the Roman harbour of Portus during early- and mid-imperial. The composition of metal objects was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This information contributes to understand the metallurgic technologies adopted in the antiquity during the production of the artefacts. Lead results major component of the tokens and others analysed artefacts. Its precise isotopic ratio measurement was performed using a multi-collector Thermal Ionization Mass Spectrometry (TIMS). This information was successful used to investigate the origin of minerals used to produce the metal. In fact, the relative abundance of 206Pb, 207Pb and 208Pb isotopes changes due to radiogenic contributes of thorium and uranium becoming a characteristic marker for a given geological area or specific mining site. The analytical results, supplemented by historical and archaeological assessments, point to mining areas of Spain (North-Eastern coast) and Sardinia being the most likely sources of metal.