Distilling zinc for the Ming Dynasty: the technology of large scale zinc production in Fengdu, southwest China

Our understanding of zinc distillation technology in ancient China has traditionally been limited by a lack of studies of production remains. The discovery of nearly 20 zinc smelting sites dated to the Ming Dynasty (AD 1368-1644) along the Yangtze River in Fengdu, Chongqing, southwest China since 2002 is allowing a detailed technological reconstruction of zinc production. This paper presents the analytical study by OM, SEM-EDS and EPMA-WDS of the production remains from three of these sites, including zinc ore, zinc metal, retorts and slag. The analytical results reveal the use of large-scale installations for zinc distillation with retorts made of pots, condensers, pockets and lids, all well designed to meet specific performance characteristics. The retorts were charged with iron-rich oxidic zinc ores, coal and charcoal; a high temperature of around 1200 °C and highly reducing atmosphere were achieved to reduce the zinc ores; the zinc vapour formed within the pots was cooled and collected in the condensers. The mass production of zinc in Fengdu was probably set up to supply governmental mints.