Investigation on restoration materials and techniques on bronze artifacts using non-invasive imaging and spectroscopic methods

Abstract

Archaeological bronze artifacts are often found in fragmented or damaged states during excavation, necessitating restoration before they can be displayed in exhibitions. However, many early restoration works lack detailed documentation, posing significant challenges for museum conservators and scientists who want to reanalyze these restored artifacts. Reconstructing past restoration processes via scientific analysis is becoming a fundamental job. Previous studies on restoration materials and techniques for bronze artifacts have mostly relied on micro-analytical and invasive techniques, which are limited in providing comprehensive restoration information about artifacts as a whole. The present study employed imaging techniques, including macro X-ray fluorescence spectroscopy, X-ray radiography, and ultraviolet-induced visible luminescence imaging, in combination with Raman spectroscopy and fiber optics reflectance spectroscopy, to investigate two bronze artifacts dated to the early Spring and Autumn period (770–476 BCE) in the collection of the National Museum of China. The results indicated that one of the artifacts, a bronze vessel (yan), exhibited extensive surface cracks and a large missing piece, which had been repaired using a copper plate joined with tin-lead soldering. Both artifacts showed evidence of surface retouching with pigments such as lithopone, lazurite, phthalocyanine blue, barium white, and chrome yellow. Lithopone, in particular, helps researchers estimate the restoration period of these artifacts, providing valuable insight into their conservation history. The integration of imaging and spectroscopic techniques proves to be an effective approach for characterizing the restoration materials and techniques applied to bronze artifacts, helping conservators in assessing the condition of restored bronze artifacts.