Innovative Study Reveals the Genius of Ancient Chinese Bronze Makers

After decades of effort by scientists and historians around the world, a pair of researchers from the United Kingdom have finally identified the mystery ingredients used by Chinese metallurgists in the first millennium BC to create a remarkable variety of Chinese bronze alloys. These enigmatic ingredients, identified only as Jin and Xi, were listed as the key elements used to manufacture bronze in an 2,300-2,500-year-old Chinese technical manual known as the Kaogong ji .

All previous efforts to discover exactly what Jin and Xi were had been unsuccessful. But now historian Ruiliang Liu from the British Museum and archaeologist A. M. Pollard from the University of Oxford appear to have cracked the linguistic code, as they explain in a new paper just published in the journal Antiquity. The scientists have identified Jin and Xi as copper-rich alloys that were concocted by ancient Chinese bronze makers to be used as the base materials for multiple varieties of bronze, a metal that could be put to many uses.

“It indicates an additional step—the production of pre-prepared alloys—in the manufacturing process of copper-alloy objects in early China,” said Dr. Liu in a press release announcing the publication of the Antiquity article. “This represents an additional but previously unknown layer in the web of metal production and supply in China.”

The two-step process used in very early Chinese bronze production reveals just how sophisticated Chinese metalmaking techniques were 2,500 years ago, surprising scientists and historians who hadn’t anticipated uncovering ancient formulas that were so complicated.

An ancient illustration depicting Chinese bronze furnace workers at work making metal. (Lui et al./ Antiquity Publications Ltd)

An ancient illustration depicting Chinese bronze furnace workers at work making metal. (Lui et al./ Antiquity Publications Ltd )

The Eastern Zhou Chinese Bronze Manufacturing Masters

The Kaogong Ji (which translates to ‘Book of Diverse Craft) comprises one section of a much larger ancient book known as the Rites of Zhou , which dates to the time of China’s Eastern Zhou Dynasty (771 to 221 BC). The Rites of Zhou consists primarily of administrative records from China’s Western Zhou Dynasty, which immediately preceded the reign of the Eastern Zhou emperors.

Inserted as an out-of-context addition to the Rites of Zhou , the Kaogong ji features six separate formulas for making bronze alloys. Each type of bronze was produced through a different mixture of the elements known as Jin and Xi, which were apparently quite versatile.

Different Chinese bronze alloy mixtures were used to make a wide range of metal items, including everything from swords to musical instruments. And the Kaogong ji spelled out which formulas should be used to make which items.

Unfortunately, the Kaogong ji wasn’t as detailed as it could have been, from the perspective of modern scholars. Since it was written and inserted into the Rites of Zhou sometime between the fifth and third centuries BC , it was presumed the readers of the manual would already know what Jin and Xi were and therefore wouldn’t need to be told.

Part of the Classic of Rites annotated edition in which the Chinese bronze formulas, using the mysterious Jin and Xi characters, were written down. (Public Domain)

Part of the Classic of Rites annotated edition in which the Chinese bronze formulas, using the mysterious Jin and Xi characters, were written down. ( Public Domain )

Historians assumed Jin and Xi must have referred to copper and tin, since these are the two metals that have always been combined to make bronze. Until Pollard and Liu took up the challenge, however, all previous attempts to recreate the ancient Chinese formulas by mixing copper and tin had failed. The bronze alloys produced from these efforts had not matched the chemical signatures of metallic coins dated to the Eastern Zhou period, which made it clear there was something essential in the formulas that chemists and materials scientists just weren’t comprehending.

In their Antiquity article, Liu and Pollard quote another academic who has studied the Rites of Zhou in general and the Kaogong ji in particular, and who wrote the following:

“The Kaogong ji is not, as a text, a technical manual. Instead, it was apparently written for use by administrative supervisors of court artisans, deliberately reducing technical information to simple formulae for their benefit. In other words, the text represents handy second-hand knowledge that did not come from the artisans themselves. This probably explains why the technical information contained in the text is often vague, and matches but very incompletely the data one can extract from the material record of Ancient China.”

This put historians and the chemists they recruited to assist them in a difficult position. They could try to recreate the formulas given for bronze, but there would have to be guesswork involved since the exact chemical definitions of the terms Jin and Xi were missing.

As it turned out, more than a century of effort was required before the truth was finally revealed. This highlights the extraordinary nature of the discovery by Liu and Pollard.

For the purposes of their research project, Liu and Pollard performed a detailed analysis of the chemical composition of Chinese coins that came from the same time as the Kaogong ji was written. Through a careful deconstruction they determined the coins were manufactured from the mixture of two types of pre-prepared metal alloys made from copper, tin, and lead in one case, and copper and lead in the other.

Using logical deduction, the experts concluded that these two alloys must be Jin and Xi. It had previously been believed that the coins were made by diluting copper with tin, up to the point where the desired mixture was achieved. However, experiments using this method produced objects that did not match the chemical formulas of the ancient coins. It required two distinct alloys to make them instead, and the parallels with Jin and Xi seem too obvious to ignore.

“For the first time in more than 100 years of scholarship, we have produced a viable explanation of how to interpret the recipes for making bronze objects in early China given in the Kaogong ji ,” Professor Pollard stated.

Science Fills in the Blanks in the Ancient Chinese Dictionary

The research carried out by Professors’ Pollard and Liu was highly unique in that it involved the use of science to solve a linguistic mystery. The true meanings of the words Jin and Xi would have remained impenetrable without the experiments that revealed the actual chemistry of ancient Chinese coins from the time of the legendary Eastern Zhou dynasty.

Logic and science helped historians uncover a truth that had been hidden in plain sight in the Kaogong ji , given that the references to Jin and Xi were first discovered nearly 100 years ago.

Top image: This Chinese knife coinage from the Eastern Zhou dynasty was used in the remarkable Chinese bronze alloy analysis study that finally revealed the hidden alloy formulas. Source: Lui et al / Antiquity Publications Ltd

By Nathan Falde

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