Ghostly images slide across QiangBing Wei’s computer screen as he operates a mouse to move samples inside a scanning electron microscope (SEM). Wei, 25, is a PhD student at the Institute of Cultural Heritage and History of Science and Technology in Beijing. He’s using the SEM to magnify millimetre-sized pieces of ancient shard to several centimetres, making them look big enough so he can examine their microstructure. Peering over Wei’s shoulder, it looks like he is viewing a series of irregular islands with Google Earth.

The institute to which Wei belongs is part of the University of Science and Technology Beijing, one of the foremost universities for metallurgy in China. Wei’s mentor is Siran Liu, who received a PhD in archaeology from Imperial College, London, for a thesis on “Precious metal production and its social significance in Imperial China”. Liu has kindly offered to show me around the institute and describe the scientific instruments his team uses for their work on “metallurgical archaeology”.

Science and history

As we take the tour, Liu explains that better instruments for such studies are found at the Palace Museum – China’s huge national museum in the centre of Beijing. Scientists there even have dedicated beam time at the Shanghai synchrotron for analysing artefacts. But Liu says he and his colleagues are less interested in the final artefacts than in the technologies that produced them in the first place.

“The finished products, such as vessels, had to fit the cultural specifications and are very similar to each other,” Liu explains. “Analysing them gives you limited information about how they were made. I like the production remains – things like slag, and fragments of furnaces and crucibles. These preserve much information about the production process.” Such information, in turn, yields information about Chinese history that would otherwise be impossible to obtain.

Indeed, where there are few surviving historical documents – or even none at all – archaeology can provide virtually the only information about the period in question. To illustrate, Liu holds up a piece of ceramic. “This is from the Lithic period – the Stone Age – about 2000 BC,” he says. “We analyse these to see what techniques [people then] used and whether they traded with their neighbours, and learn about the economic activities of the era.”

In other instances, the institute’s work extends stories told by historians. Recently, for instance, Liu’s group studied lead-silver smelting during the Song dynasty (AD 960–1279). It was a period of huge demographic and technological changes, in which paper became widely used, printed books began to circulate, and China switched from an oral culture to one of the written word.

I like the production remains – things like slag, and fragments of furnaces and crucibles. These preserve much information about the production process

Siran Liu, University of Science and Technology Beijing

Among the technological developments in the Song dynasty was a big shift from furnaces to crucibles in the lead-silver smelting process in northern China. Another was a switch from using charcoal as a fuel to coal due to the impact of deforestation. But were these two changes related? And what impact, if any, did they have on other contemporary events? Research at the institute has discovered an intriguing link between them.

It turns out that early methods involved charcoal-fuelled furnaces placed in the centre of the ores. But the furnaces could not be loaded directly with coal, for coal softens as it heats up and then burns, which could cause the furnace to collapse. To use coal, the Chinese therefore needed to alter the smelting process, placing ore-containing crucibles inside the fuel rather than having the ore surround the furnace. This in turn meant it was better to locate smelting sites nearer the coal mines than the ore mines, for the necessary amount of coal was harder to transport, prompting demographic shifts as people moved closer to the smelting sites.

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Archaeological metallurgy can also test historical narratives. Liu’s group, for example, is studying Chinese silver of the 17th century – the late Ming period. According to conventional historical accounts, China once had silver mines, but these eventually declined. When global trade developed in the 1600s, the story continues, products from thriving silver mines in South America, as well as Japan, began to inundate the European market. Taking advantage of the inexpensive silver, European travellers traded it in China for luxury items such as silk and porcelain.

“Is this story true?” Liu asks. “Well, we can find that out.” As he explains, the ores from different geological settings have different isotope ratios. The isotopic fingerprints of Chinese and South American silver are therefore different. Techniques such as lead-isotope analysis with induced coupled plasma mass spectrometry (ICP-MS) can be used to match these fingerprints in China’s silver, so that Liu’s team hopes to be able to answer the question definitively.

This year, members of Liu’s group, together with colleagues from Peking University, attended a summer smelting school in Hunan to hone their techniques. There they conducted experiments in ancient production methods, reconstructing ancient furnaces and firing them using traditional hand-powered bellows. “It’s exhausting,” Liu says. “You can do it for only 10 minutes at a time, and we have to take turns.”

The group then studies the effects of firing on their furnace materials, and compares them with archaeological samples of furnace materials. This work can reveal how ancient furnaces worked, the conditions under which artefacts were created, and what materials were fired. “All that information is trapped in this glassy remains,” says Liu, holding a small furnace fragment.

The critical point

As philosophers and historians have demonstrated, many technologies of the past several hundred years – for instance in agriculture, transportation, information and communication – have shaped human society and culture more significantly than battles and political victories. Liu and his colleagues are now using metallurgical tools to push such demonstrations back, not just hundreds but even thousands of years.