Investigation of the Altered Layer on Ancient Chinese Bronze Mirrors and Model High-Tin Bronzes

Many ancient Chinese bronze mirrors have a smooth patina. An ingress of corrosion to a depth of approximately 100 μm is found beneath the patina. The corrosion selectively replaces the Cu-rich α phase leaving the Sn-rich σ phase intact. Previous work by x-ray diffraction has shown that the a-phase replacement product is poorly crystallized or nanocrystalline SnO2. Transmission electron microscopy was employed to further characterize the replacement product in both ancient mirror and replication samples. Nanocrystalline SnO, in the form of small spheroids has been found. Remnants of an original alloy phase appear to be interspersed with the tin oxide.