As the fourth most abundant metal on Earth, zinc (Zn) smelting was once a major challenge in the history of human metallurgy. Elementary zinc has a melting point of 419.5°C and a boiling point of 906.97°C, but it is highly volatile when the reduction temperature exceeds 1000°C, and zinc vapor re-oxidizes into zinc oxide upon contact with air. This property meant that obtaining elementary zinc in ancient times required breaking through two key technical bottlenecks: high-temperature sealed reduction and efficient vapor condensation. For this reason, only China and India mastered zinc smelting technology globally before the 18th century.
In ancient China, zinc was called "woqian" or "baishuiqian (white water lead)", and its core use was to produce brass (a copper-zinc alloy). Brass was not only used for coinage (e.g., Tongbao coins of the Ming and Qing dynasties) but also widely applied in imperial court etiquette utensils, Buddha statue casting, and daily necessities. According to historical records of the Qing Dynasty, the annual output of lead-zinc in Guizhou reached 41.95 million kg (8.39 million jin), with a total output exceeding 436 million kg (872 million jin) over 104 years. Sichuan, Hunan, and Guangxi were also important production areas. More notably, Chinese zinc ingots were exported to Japan and Europe via maritime trade—zinc ingots salvaged from a Swedish sunken ship in 1745 had a zinc content of 98.99%, confirming the maturity of China’s zinc smelting technology at that time.
Since the 20th century, scholars have gradually uncovered the technical code of ancient Chinese zinc smelting through textual research, artifact analysis, and field investigations:
Debates on Literary Origin: Based on the analysis of zinc content in coins of the Xin Mang period (9–23 AD), Zhang Hongzhao (1923) argued that zinc use in China began in the Western Han Dynasty (202 BC–8 AD). Wang Jin, however, proposed a four-stage theory: (1) zinc mixed in lead during the Han and Tang dynasties; (2) brass smelting with calamine in the Tang Dynasty; (3) increased zinc use in coin casting in the Song and Ming dynasties; (4) elementary zinc smelting in the mid-Ming Dynasty. The theory of an origin in the Five Dynasties once prevailed due to the record in Treasure Treatise ("woqian can extract gold"), but Zhao Kuanghua pointed out that this was an annotation added by Li Shizhen, not part of the original text.
Debates on Process Principles: Regarding the "smelting of woqian" recorded in The Exploitation of the Works of Nature, Yang Weizeng proposed the "reflux method", while He Tangkun confirmed it as the fractional condensation method through physical and chemical analysis: zinc ore and coal were placed in a clay pot; after high-temperature reduction, zinc vapor crystallized in the condensation cavity at the top of the pot. This process is highly consistent with artifacts unearthed from Ming Dynasty sites in Chongqing.
Breakthroughs in Fieldwork: In the 1980s, Hu Wenlong and Xu Li discovered traditional zinc smelting workshops in Hezhang, Guizhou, and completely restored the "in-pot reduction + top-pot condensation" process. Mei Jianjun further pointed out that the landmark innovation of Chinese zinc smelting technology lay in the detachable ceramic condenser, which stood in sharp contrast to the fixed stone-built condensation devices at the Zawar site in India.
Since the 21st century, zinc smelting archaeology—focused on site excavation and scientific testing—has achieved three major breakthroughs:
Radiocarbon dating confirmed that the smelting pots and zinc ingots unearthed from the Miaobeihou Site in Fengdu, Chongqing (2004 excavation) date to the Ming Dynasty. Tests showed that smithsonite (ZnCO?) and coal were used, with a zinc recovery rate of 92%. The Dafengmen Site in Shizhu (Qing Dynasty) demonstrated technological evolution: the height of smelting pots increased from 30 cm to over 40 cm, and furnaces became slimmer to improve thermal efficiency. The 2013 excavation of the Linjiang Erdai Site in Zhongxian uncovered 125 smelting relics, confirming that the Chongqing area had formed a complete industrial chain covering mining, smelting, and transportation.
The Tongmuling Site in Guiyang, Hunan (one of China’s Top 10 Archaeological Discoveries in 2016) was the first to reveal integrated smelting of zinc-copper-lead polymetals: trough-shaped furnaces processed different ores in zones, and metal separation was achieved by controlling the reducing atmosphere. Residues of zinc crystals were found on the inner walls of distillation pots unearthed at the site, with lead-tin alloy attached to the outer walls—confirming the practical application of the "lead precipitation and silver extraction" method recorded in The Exploitation of the Works of Nature. More crucially, the site supplied raw materials for coinage at the Baonan Mint of the Qing Dynasty, and some zinc ingots were exported to Southeast Asia via Guangzhou.
Studies of sites in Luocheng and Huanjiang, Guangxi, found an interactive reaction between zinc vapor and silver-lead ore in "macao furnaces" (horse-trough furnaces), confirming that China invented the "silver-zinc crust method" (precursor to the Parkes process) in the late Ming Dynasty: zinc formed alloy dross with gold and silver, and zinc was then separated by distillation. This technology predated the British Parkes process by two centuries, rewriting the history of global precious metal refining.
Despite significant progress in research, three key issues remain to be explored:
Missing Link in Origin: The earliest physical evidence of zinc smelting currently dates to the Ming Dynasty, but zinc content in Han Dynasty coins and literary records from the Five Dynasties suggest an earlier origin. It is necessary to find smelting relics from the Song and Yuan dynasties.
Cross-Regional Linkages: How were zinc ores from Guizhou transported via the Yangtze River to Chongqing for refining? What was the trade volume of Hunan zinc ingots via the "Maritime Silk Road"? Quantitative research combining shipping archaeology and foreign trade archives is needed.
Bottlenecks in Site Activation: Most zinc smelting sites are located in remote areas (e.g., the Qiyao Mountain area in Chongqing, the hilly areas of southern Guangxi). Protection efforts must overcome geographical constraints. It is recommended to reference the model of the Rammelsberg Mining and Metallurgy Park in Germany, using digital twin technology to restore the zinc smelting process and combining eco-tourism to promote industrial civilization.
From the "smelting of woqian" illustrations in The Exploitation of the Works of Nature to the zinc ingots in sunken ships, from the mines in Guizhou to the silver furnaces in Japan—the history of ancient Chinese zinc smelting is not only a story of technological evolution but also an epic of material flow on the eve of global industrialization. It reminds us that beyond the glory of bronze and iron, this silver metal once called "woqian" or "baishuiqian" quietly supported an empire’s monetary system and crossed oceans to reshape the trajectory of metallurgical technology in Eurasia.
9 new sites (including Yuyouchi Ridge in Youyang and Linjiang Erdai in Zhongxian) have been added to the Chongqing zinc smelting site group, bringing the total to 29.
11 new zinc smelting-related mines have been discovered in Guiyang, Hunan, confirming the Qing Dynasty "zinc ore → coin casting → export" industrial chain.
Zinc isotope characteristic values have been detected at sites in Hechi, Guangxi, providing new evidence for tracing the cross-border trade of zinc ingots.
(This article is reconstructed based on archaeological reports and scientific literature; see Chongqing Zinc Smelting Site Group and Compilation of Metallurgical History Materials from Guiyang, Hunan for original research.)
