Cupronickel/Baitong 白铜 (also paktung)
Two kinds of white copper were known. Arsenic copper with a relatively high arsenic content exhibits high hardness and is almost silver in colour. The material was known and produced by alloying in the early bronze age in the Near and Middle East. However, as arsenic bronze played only a very minor role in East Asia, this type of bronze was apparently also little used in antiquity.
The second alloy uses nickel. Cupro-nickel is similar to silver in colour, but possesses high hardness and moreover does not oxidise and thus stays shiny without polishing. This metal was extremely valued and widely marketed in late imperial China. Occasional exports from Guangzhou brought it to Europe, where it came to be known as paktung (from the Cantonese pronunciation) and regarded as extremely precious. Due to European fashion and the turmoil of modern Chinese history, Chinese baiting objects are now most readily studied in European museums (Huang Chao). Incidentally, a German chemist of the late 18th century worked out that nickel was the decisive alloy component.
Baitong first appears in Huayang guozhi 华阳国志 (354 CE) as a metal that came from what is now northeastern Yunnan and western Sichuan. On account of the presence of late imperial baitong mines in Huili 会理, and known copper and copper-nickel deposits in the region, this metal has been identified as cupro-nickel (Yang Shouchuan 2014, 24). This is not entirely certain however, as arsenic oxide (pishi 砒石) was also known for the region. Moreover, alchemists of the 4th century produced white copper by melting copper in the presence of arsenic oxide.
By the Ming period, baitong objects became widely appreciated. Private writings note that all baitong came from Yunnan and differentiated between true baitong and the cheaper alternative made by smelting copper with arsenic. Both metals were extremely valuable, priced higher than gold.
No late imperial sources mention the composition of the true baitong of Yunnan. This suggests that production used copper-nickel ores and did not involve the extraction of nickel and the alloying of the two metals.
Names of baitong mines are recorded in Qing sources. They are located along a narrow, mineralized zone that extends from northern central Yunnan to Huili in Sichuan. It appears that the two registered mines located in Yunnan province were exhausted by the mid-Qing, and the alloy in fact was produced by mines in Huili.
This project has geolocated the recorded sites, but will investigate them only as far as work economy permits.
