In-situ non destructive investigation of outdoor bronze sculptures

Abstract

Abstract Indoor investigations are commonly used to assess the causes and extent of damage to bronze artwork and cultural heritage items; however, these methods typically involve destructive sampling and outdoor bronze sculptures are typically heavy and large, hindering their transport. In this study, 16 bronze sculptures exposed to outdoor environments for a period exceeding 20 years were evaluated in-situ to develop a non-destructive prediction model that can identify types of corrosion and quantify the amount of corrosion on bronze sculptures that cannot be easily transported. The sculptures were classified into three groups according to their patina chromaticity, reflectivity, and chemical composition. The corrosion characteristics were found to be copper oxide and sulfide patinas. Chromaticity and reflectivity investigations revealed that the chemical composition changes of the patinas corresponded to the formation of corrosion products, thus showing a high potential for the identification of the type of corrosion. Portable XRF spectroscopy showed that the low error rate of Cu make its compositional behavior a good indicator in identifying the type of corrosion of sulfide and chloride patinas. Portable Raman spectroscopy was able to detect basic sulfides such as brochantite, antlerite, and cuprite. The high potential for the application of portable Raman spectroscopy was confirmed by results of previous artificial patina corrosion experiments obtained through XRD and bench-top Raman spectroscopy. The corrosion types and corrosion products on the bronze sculptures could be identified using chromaticity and reflectivity, portable X-ray fluorescence, and portable Raman spectroscopy. Therefore, this study confirmed the feasibility of using portable non-destructive analytical equipment in outdoor environments to identify corrosion types and quantify corrosion amounts for large, heavy bronze sculptures. The rapid insitu diagnosis of these corrosion attributes is expected to contribute to establishing conservation treatment plans in the future.