Managing Corrosion Risks in Underwater Cultural Heritage: A Preventive Conservation Strategy for the Belinho I Shipwreck Pewter Assemblage (Esposende, Portugal)

This paper addresses corrosion risk management for pewter objects from the Belinho I shipwreck (Esposende, Portugal). A collaborative framework was established, involving community stakeholders during the critical post-recovery phase, leading to the development of both field community and laboratory preventive conservation protocols. During the second phase of the laboratory protocol, a crowned-hammer hallmark was identified, consistent with others in the assemblage. The third phase of the laboratory protocol implemented a progressive sequence of passivation baths guided by Pourbaix diagrams and systematic monitoring of physicochemical parameters (Eh, pH, conductivity, and temperature). Characterization of primary corrosion products and precipitates from the baths, using 3D digital microscopy, SEM/EDS, µ-Raman, and XRD, identified basic tin chlorides with abhurite and hydroromarchite structures. Collectively, results demonstrate that immediate preventive conservation is an effective strategy for controlling corrosion risk, underscoring the necessity of collaborative frameworks for the long-term safeguarding of underwater pewter heritage.