A Study of Protective Coatings for Archaeological Silver

This study investigates the sustainability and efficacy of coatings for archaeological silver. Building on a survey of current practices in silver conservation and a literature review, a group of Chimú (Peruvian north coast, 1100–1400 CE) silver alloy items in the National Museum of the American Indian collection serves as a case study. Assessing treatment options for 80 Chimú items led to the investigation into the implications of introducing a new coating campaign. Experimentation was carried out with coupons approximating the composition and manufacture of Chimú silver. Four conservation grade materials, Agateen® 27, Acrysol® WS24, Paraloid® B-72, and Regalrez® 1126, were tested for protection efficacy in a humid, sulfur-containing environment. Analysis with X-ray fluorescence spectroscopy (XRF), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), and imaging at several phases throughout the experiment provided data on the interaction of the metal and the coating and the effects of coating and re-coating. Oddy testing and Fourier transform infrared spectroscopy (FTIR) conducted on these prepared coatings helped determine their suitability for long-term use. Results indicate that not coating is more appropriate for preservation than coating with any of the four materials tested.