Investigation and replication of the surface microstructure of early Chinese black bronze mirrors

Abstract

Many ancient Chinese bronze mirrors have survived with their original surface decorations intact, particularly those with glassy black surface coatings. The microstructures and compositions of cross-sectional samples from ancient mirrors have been analyzed with optical and electron microscopy and synchrotron x-ray fluorescence. The core has a two-phase metal structure while the surface shows evidence of selective dissolution of copper from the {alpha} (Cu-rich) phase. The {alpha} phase regions are replaced pseudomorphically by a mineral product with the {delta} (Sn-rich) phase remaining metallic. A fundamental study of the electrochemistry of the copper-tin system has given information on the conditions under which selective dissolution of copper takes place. Electrochemical polarization has been used to drive the copper dealloying process in cast high-tin bronze. The resulting microstructure is similar to the dealloyed microstructure observed in the ancient samples.