In 2022, a bronze mirror with an inscription was unearthed from a tomb at Yaozhuang, Liuhe District, Nanjing, dating to the late Ming and early Qing Dynasties. This mirror was originally from Japan and introduced into China through commercial exchange. The mirror is fragmented and lacks a handle, and its decorative surface is covered with a layer of silver white material, resembling a “mercury shower”. To understand the production process, composition, and preservation status of the silver white coating on the mirror surface, microscopic observation, Raman spectrometry, and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) were used for analysis. The results show that the mirror was cast from a copper-tin-lead ternary alloy, and the silver white substance on the surface is cassiterite, formed through long-term corrosion in the burial environment. The bronze mirror is severely corroded, and the body has been basically mineralized.