Gold refining by cementation with salt at Sado in early seventeenth century Japan

In the seventeenth century Japanese gold production became the highest rank of the world and Sado gold contributed nearly half to the domestic production. The key technology of massive gold production was gold-silver parting by cementation process with salt. During the excavation of the Sado Bugyosho (magistrate office) site, in 1996, gold refining remains were found below the 1647 fire horizon. A total of 29 furnaces were found in an area of east-west 17 m by north-south 8 m. The largest furnace is an elongated shallow tray-like furnace, which resembles closely the cementation furnace illustrated in eighteenthand nineteenth-century picture scrolls of the mine. Large number of fragments of earthenware such as clay dishes, clay plates and clay rods were unearthed. Many of the earthenware were discolored from the original reddish color. The chemical compositions of discolored samples are characterized by increase in Na₂O, K₂O, S, Cl and Ag, and decrease in SiO₂ and Fe₂O₃ indicating the gold-silver parting reaction by common salt.