Researchers believe they've found the key to a thriving metal industry in ancient China in a 2,300-year-old recipe for bronze. Some 1.5 tons of bronze discovered in the tomb of a general from the Shang dynasty (1600BC to 1046BC) in 1976 helped show the "massive scale" of bronze production in imperial China, University of Oxford archaeologist Mark Pollard tells Science, which reports it "far outstripped anything occurring in Europe at the time." Now Pollard and Ruiliang Liu, an early-China curator at the British Museum, say they've discovered how the Chinese accomplished such a feat, contained in an ancient recipe for bronze.
The technological encyclopedia Kaogong ji, which dates to 300BC, contains six recipes for casting bronze objects using two main ingredients: "jin" and "xi." These were initially assumed to be copper and tin, the main components of bronze. But attempts to reconstruct the metal under that interpretation have failed over hundreds of years, says Liu. That's because it was too simple, according to the researchers, who analyzed the chemical composition of Chinese coins minted around 300BC. It revealed they were made by mixing two specific alloys: one of equal parts copper and tin and another of copper, tin, and lead with a ratio of 80:15:5, per New Scientist.
These alloys are likely "jin" and "xi," according to the study published Wednesday in Antiquity. The researchers believe the alloys could have been prefabricated as ingots and distributed to foundries, a sign that metalsmithing was far more complex than previously known. "It indicates an additional step," Liu tells CNN. Jianjun Mei, an archaeo-metallurgist at the University of Cambridge, notes the authors of Kaogong ji were likely administrative officials rather than craftsmen, therefore they might have gotten the exact ingredients wrong, per Science. But he adds there's "no convincing analytical evidence to support" the claim that "jin" and "xi" are not pure copper and tin. (More Bronze Age stories.)
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