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.

► This is the first detailed reconstruction of zinc distillation technology in Ming China. ► Fengdu zinc smelting employed multi-component retorts with pots, condensers, pockets and lids. ► All the parts were well designed to meet specific performance characteristics. ► The pots were charged with iron-rich oxidic zinc ores, coal and charcoal. ► Zinc vapour formed within the pots at ∼1200 °C and was collected as a solid ingot in the condensers.