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Researchers decipher mysterious ancient recipe for bronze | Science

In 1976, archeologists excavated more than 1.5 tons of bronze from the 3000-year-old tomb of Fu Hao, a Chinese general in the Shang dynasty. The number of artifacts reflected the scale of bronze production in imperial China, which far outstripped anything occurring in Europe at the time. Now, by reinterpreting a mysterious recipe for bronze in a 2300-year-old text, researchers say ancient foundries in China relied on pre-prepared alloys–which points to vast supply chains supporting an even more complex bronze industry than previously suspected.

“China was producing hundreds of tons of bronze a year,” says Mark Pollard, an archaeologist at the University of Oxford and co-author of the new study. “It’s a massive scale and it’s a really important part of the imperial economy.”

For decades, archaeologists have scrutinized an ancient text known as the Kaogong ji, a technological encyclopedia with parts that originated some 2500 years ago. It contains instructions on how to make carriages and musical instruments, and even holds rules for building a city. It also contains six recipes for casting bronze objects such as axes, swords, and vessels used in ritual ancestral worship. The recipes rely on two main ingredients: jin and xi. Scholars had previously suggested these were copper and tin, the components of bronze. But bronze artifacts from the time also contain high levels of lead.

To get a better sense of what jin and xi might be, Pollard and Ruiliang Liu, an early-China curator at the British Museum, decided to look for clues in previous chemical analyzes of ancient bronze coins. The majority of such coins could be made by mixing two specific alloys–one of copper, tin, and lead, and another of copper and lead, they report today in Antiquity.

Pollard and Liu propose these two alloys, which could have been prefabricated as ingots and distributed to bronze foundries, are jin and xi. “We think this pre-alloying argument answers some of the questions archaeologists have had for a long time,” Liu says. The prefabricated ingots would also add an additional layer of complexity in the production, transport, and supply of metals in ancient China, Pollard says. “There’s a much bigger network of control and supply, and we really don’t understand how that happens.”

Jianjun Mei, an archaeo-metallurgist at the University of Cambridge, is skeptical. “There is no convincing analytical evidence to support their claim that jin and xi are not pure copper and tin, but pre-prepared alloys,” he says. He says the presence of lead in some bronzes can be explained using the theory that the Kaogong ji was written by administrative officials and not craftsmen. “These officials might only pay attention to the most important materials – copper and tin.”

Yet Mei still welcomes the paper’s attempt to reinterpret the recipes. He says knowing how the ancient bronze artifacts were made helps researchers understand the civilizations that used them. “We have no idea where these objects–the statues or vessels–were made, who made them, and where the material came from,” he says. “The first step is to understand the technology that was used” to make the bronze.

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