Characterization of corrosion products formed on bronze ornaments excavated from the Chu tombs of the Spring and Autumn Periods in Dangyang, China

Abstract 130 corrosion products on bronze ornaments excavated from the Chu tombs of the Spring and Autumn periods in Dangyang, Hubei Province, China, were examined by X-ray diffraction, and statistically analyzed. The results showed that the main corrosion products were cassiterite (SnO2), copper sulfates, and sulfides, and the rare tenorite (CuO). And corrosion products of different colors such as blue-green and black-gray were specifically detected by Raman spectroscopy. The Raman spectra of blue-green corrosion products were identified as Cu hydroxide sulfates and Cu hydroxide carbonate such as brochantite, posnjakite, antlerite and malachite, the black-gray corrosions were confirmed as copper sulfides, only the good quality Raman spectrum of covellite was obtained. The shifts of certain band positions in different Raman spectra of the black-gray corrosion products, as well as the causes of D and G peaks in the spectra were discussed. And the advantages and disadvantages of using Raman spectroscopy for the identification of corrosion products were presented and discussed. Finally, with reference to previous literature, it was proposed that the SO 42 - ions and sulfate-reducing bacteria in the soil, along with the closed and anoxic burial environment, may explain the sulfate and sulfide corrosion products on the bronze ornaments. The presence of tenorite and charcoal indicates that the tombs might have undergone fire.