# The Brass Gap: How Ancient Crucibles Filled a 600-Year Historical Gap

*New chemical and isotopic analysis of ninth-century crucibles provides the first direct evidence of brass production in medieval East Asia*

By Sandee Oster · Published 14 August 2026 · Updated 15 August 2026

Source: https://archaeologyteahouse.com/stories/the-brass-gap-how-ancient-crucibles-filled-a-600-year-historical-gap

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![Brass 1(2)](https://archaeologyteahouse.com/media/01a0068b-28b3-7703-88f6-3d6b6eb56473/1600.webp)

*Brass-making crucibles. Credit: Xiao et al. 2026*

We have all heard of them, the famous ages of archaeology: there is the Stone Age, the Bronze Age, and the Iron Age. Exactly when each age began or ended in any given civilization or culture varies slightly. I recently learned that the Philippines has a Stone and Metal Age, because bronze and iron arrived and were used roughly simultaneously, so the Metal Age was chosen as a term in lieu of Bronze and Iron. But why only those three? Why no Brass Age, for example?

Brass was an important part of many ancient cultures, and knowledge of how to make it spread across the ancient world at different times. Well, for one, the three-age system was developed by the archaeologist Christian Jurgensen Thomsen, and he based it on the dominant tool material at the time (sometimes these materials overlapped, but that’s a different problem). Brass was never the dominant metal, but that doesn’t mean it wasn’t important.

In ancient China, written accounts of brass production date back to the 10th century, but direct physical evidence has so far eluded archaeologists. In fact, no direct physical evidence of brass production existed anywhere in East Asia before the 1500s.

That is, until Dr. Hongyan Xiao and his colleagues discovered crucibles (containers used to melt metal) in Guangzhou. Of course, crucibles could be used to melt any metal. Still, systematic analysis using Portable X-ray fluorescence (pXRF), Scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and Lead isotope analysis (MC-ICP-MS) showed that what was smelted here over 1000 years ago was brass.

### The Importance of Brass

![](https://archaeologyteahouse.com/media/01a01d25-82e1-721a-b3f4-51577dae651e/960.webp)

*Guangzhou excavation site, photos of the crucibles, a brass earring, and a furnace all in situ. Credit: Xiao et al. 2026*

Brass is a copper-zinc alloy that first became a major industry over 2,000 years ago in the ancient Mediterranean, where the Greeks and Romans knew it as ‘orichalcum’. From there, the knowledge of smelting the metal spread through trade routes, political contacts, and migration. By the 6th to 7th centuries AD, brass production had reached Iran, by the 8th century, Central Asia, and finally East Asia by the 10th century.

However, in China, scholars have had to infer brass production from historical texts and chemical fingerprints (lead isotope signatures) in brass objects, suggesting local production. But actual direct evidence that brass was being produced in China rather than simply being imported was lacking: no crucibles, no furnaces, and no slag.

This gap made it difficult to understand how brass making worked in East Asia and how it connected to other traditions across Eurasia.

To address the gap, the researchers looked to Guangzhou.

Guangzhou has been a major metropolis in southern China since the medieval period, serving as an important hub of international transactions. In fact, Dr. Xiao described it as a medieval oriental version of Dubai or Singapore. So, you can imagine it as a lively bustling hub of trade, craft, and business.

Excavations at Guangzhou between 1975 and 2007 uncovered a metalworking workshop that operated from the 3rd to 18th centuries AD. Here, various objects made from copper alloys, silver, and iron were produced for over 1000 years. Among the remains, archaeologists uncovered nearly 80 crucibles and crucible sherds spanning the workshop’s entire lifetime. One set of crucibles, dated to the 7th-10th centuries, was of particular interest and was further subdivided into two periods.

### A Hint of Brass

![](https://archaeologyteahouse.com/media/01a01d25-8dbf-7614-a85e-d5c48af7e14b/960.webp)

*Zinc levels in the crucibles over time, marking the shift from earlier bronze-working to later brass production. Credit: Xiao et al. 2026*

To examine the crucibles, the researchers used a variety of methods, including pXRF analysis to scan the crucibles’ interiors and detect levels of copper, tin, zinc, and lead.

Using SEM-EDS, they analyzed cross-sections of crucible fragments to understand how each one was built (ceramic body, protective outer coating, and inner lining). Tiny droplets of leftover metal trapped in the glassy residue confirmed the presence of zinc-rich compounds such as willemite and zinc oxide, and detected actual brass droplets.

Finally, they conducted lead isotope analysis of the metal residues to trace their geological origin, which, in turn, helped confirm whether the metal was of local (southern Chinese) or foreign origin.

Together, the methods showed that before the 7th century, workers mainly processed copper, tin, and lead with almost no zinc, but then something happened: zinc levels began to rise, spiking in the 9th–10th centuries. The jump indicates that workers had begun deliberately working with zinc materials, a hallmark of brass production.

Meanwhile, the SEM-EDS revealed two brass-making recipes, one in which copper and zinc were mixed, the other where bronze (which is a copper and tin alloy) was mixed with zinc to make something called ‘gunmetal’.

Together, both lines of evidence showed that workers in Guangzhou were making brass, but where did the material they used come from?

The lead isotopes indicated the Cathaysia region in southern China, suggesting the copper and zinc used to produce brass were local.

### The Story of Brass in China

![](https://archaeologyteahouse.com/media/01a01d25-94d1-7f89-8377-a12a9c8a30f5/960.webp)

*Micrographs of the crucible’s layered structure: the ceramic body, an inner lining coated with melted metal residue, and an outer protective coating. Credit: Xiao et al. 2026*

By the 9th to 10th centuries, Guangzhou had developed a genuine brass-making industry, like that run by local governments. Guangzhou craftsmen made brass through a process called cementation: they packed metallic copper (or bronze), zinc ore, and charcoal into small crucibles and heated them above 950°C. This bonded the zinc ore to the copper, forming brass.

The furnace found in Guangzhou even gives insight into the scale of the production. Around 19 crucibles could fit in the furnace at any given time, which would result in around 33–50kg of brass per batch. Interestingly, no crucible lids were found at Guangzhou. 

This could mean one of two things: a) the crucibles were unlidded, which would require higher firing temperatures for the needed reactions and production of brass, or b) the lids were recycled after use and turned into a new set of crucibles, with any serving lids simply not recognized or found in other excavations.

The detail matters because it provides a hint at how brass-making knowledge might have arrived in China.

After the Tang dynasty lost control of the Silk Road in the 8th century, sea travel became the primary channel for connecting China with the wider world. This meant China was connected to major ports in Southeast Asia, India, and the Persian Gulf, including those linked to the Islamic world. In fact, various historical records describe thousands of foreign trading ships, many of them Arab, arriving at Guangzhou.

And you know what was happening in the Islamic world? Brass makers used unlidded techniques rather than the lidded techniques used in the Roman world. This suggests that knowledge of brass making might have been passed to China via the Islamic world rather than overland through Central Asia.

These contacts weren’t just fleeting, either, with Guangzhou hosting a foreign community of up to 20,000 people. In fact, archaeologists have found Persian-style pottery at the Nanyue Palace site, suggesting an Arab presence.

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There we have it, physical evidence that China was making brass in the 9th and 10th centuries, finally backing up historical accounts and filling a nearly 600-year-long gap in the record.

The discovery does more than just fill a gap; it reshapes how we think about the spread of brass technology across the ancient world. Rather than trickling east along the overland Silk Road through Central Asia, the evidence points to the Islamic world and a journey by ship through the bustling coastal hubs.

There is no official Brass Age, but if there were, China’s could now be definitively stated to have begun in the 9th to 10th centuries AD.

Why do you think evidence of brass making was so difficult to find when textual evidence suggested it? And where are the brass-making workshops of the 11th to 15th centuries, and why haven’t they been identified?

*Let me know your thoughts, and if you’d like to support the countless hours I pour into researching, writing, and bringing these hidden corners of history to life, why not *[*Buy Me A Coffee*](https://buymeacoffee.com/sandeeoster)

### Reference

Xiao H, Yue X, Li Z, Liu Y, Cui J. Brass technology transmission via maritime routes: crucible evidence from southern China. *Antiquity*. Published online 2026:1–19. doi:10.15184/aqy.2026.10373