Application of scanning electron microscopy and energy-dispersive x-ray spectroscopy in the study of bronze disease on ancient copper-based artifacts

Abstract

Bronze disease is a severe type of degradation in ancient copper-based artifacts and poses challenges to their preservation. This “disease” is an active cyclic corrosion process primarily caused by chlorine, oxygen and moisture. Products formed during this process, such as cuprous chloride (CuCl), continue to spread across the artifact’s surface until all available oxygen is consumed, resulting in irreversible destruction. Bronze disease is difficult to distinguish from other corrosion processes, leading to inaccurate assessments of the degradation mechanisms affecting the artifact. Combined scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) is a viable method for analyzing bronze disease in ancient artifacts and for differentiating it from other forms of degradation. This study investigated suspected bronze disease on a Chinese cast bronze vessel dating from the 11th – 10th century BCE, part of the collection at the Royal Ontario Museum in Toronto, Canada. Corrosion product sampled from the vessel using two different methods, was chemically and topographically analyzed using SEM-EDS. The first method involved the removal of corrosion product using a scalpel, resulting in the collection of mixed particles. The second method, involving the creation of replicas, utilized an adhesive to directly remove the corrosion product, capturing the particles in their original locations. The sampled material contained copper and chlorine, consistent with the presence of bronze disease, though further work is required for confirmation. Although both techniques can investigate bronze disease, the replica technique offers a more promising approach, as it enables more precise, site-specific analysis of the corrosion product.