Corrosion characteristics of fire-gilded bronzes excavated from the Jiulongshan Han tomb in Qufu, Shandong Province

The fire-gilded bronzes excavated from the Jiulongshan Han Tomb in Qufu are in urgent need of conservation and restoration due to severe corrosion. In this study, five fire-gilded bronze chariot and horse artifacts were selected to systematically investigate their material composition, manufacturing techniques, corrosion morphology, and corrosion product phases using a metallographic microscope, scanning electron microscope (SEM-EDS), and Raman spectroscopy. The results indicate that the thickness of the gilt layer ranges from 1.6 μm to 13.9 μm, and it is primarily composed of an Au-Hg-Cu ternary alloy. The presence of residual mercury confirms the application of the fire-gilding process. The copper matrix consists of a Cu-Sn-Pb ternary alloy, with grains exhibiting homogenized characteristics due to casting and gilding-related heat treatments. Corrosion states are categorized into two types: partial mineralization and complete mineralization. The cross-sectional structure, from outermost to innermost, comprises a diffusion deposition layer, a gilt layer, and a mineralized layer (with a transition layer present in some samples). During corrosion, copper ions migrate through pores in the gilt layer, while tin becomes in situ via oxidation and lead accumulates at the surface. Raman spectroscopy revealed that the corrosion products include mimetite, arsenianpyromorphite, cerussite, azurite, malachite, and other phases, indicating that the fire-gilded bronze artifacts underwent corrosion reactions with soil-borne elements such as Cl and P during burial. This study provides scientific insights into the corrosion mechanisms and conservation-restoration of Han Dynasty gilt bronzes.