Tin determination in fistula seals from Conimbriga and Augusta Emerita

Most Roman hydraulic systems were made with lead plumbing manufactured by casting lead sheets which were sealed by joining the edges with a molten metal. Modern studies suggest that the Romans used distinct techniques for joining the lead pipes (fistulae aquariae), such as welding (with lead) and soldering (with a tin-lead alloy). Micro-EDXRF and micro-PIXE analyses were used for micro-chemical characterization of joining areas of 13 water lead pipes collected in Roman archaeological contexts from Conimbriga and Augusta Emerita. Results indicate that two lead pipes from Conimbriga were sealed with a solder alloy, having a Sn content close to the eutectic point (61.9 wt.%). The remaining fistula seals have relatively low contents of Sn and also of other elements such as Sb and Cu. Micro-analyses carried out along the pipes and welding regions show the use of lead with some impurities on both areas, while the elemental mapping of tin-lead solders shows the presence of the α (lead-rich) and β (tin-rich) phases.