The study, published in the journal Archaeological and Anthropological Sciences, examined twelve copper-based artefacts, seven slag fragments and a single ore fragment, all recovered during excavation campaigns directed by E. O. Negahban in the 1970s and H. Tala’i in the 1990s. The researchers deployed an impressive analytical arsenal: optical microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy to reveal microscopic structures, inductively coupled plasma optical emission spectroscopy to pin down elemental compositions, wavelength-dispersive X-ray fluorescence for the slags and ore, and lead isotope analysis by multi-collector mass spectrometry to trace the geographic fingerprints of the metal. Each technique interrogates a different aspect of the metallurgical story, from the chemistry of the alloy to the temperature of the furnace.

The compositional results delivered a surprise. Of the twelve artefacts, eight turned out to be unalloyed copper, while only four were tin bronzes, and three of those four dated to the Late Bronze Age. In the Iron Age I samples, just one object was a bronze. This pattern hints at a shift from tin bronze in the Late Bronze Age toward predominantly plain copper in the early first millennium BCE, although the researchers are careful to stress that a sample of twelve objects cannot support claims about a site-wide technological transition. Corrosion further complicates the picture: one bronze measured an implausible 28.6 percent tin, an artefact of intergranular corrosion and copper leaching over millennia of burial rather than an intentional recipe, meaning the true tin contents were likely below fifteen percent.

Under the microscope, the metal told an even richer story. Every artefact displayed a single-phase copper matrix studded with dark non-metallic inclusions of two distinct types. Rounded inclusions rich in copper and oxygen point to copper-oxide phases, while elongated inclusions composed of copper and sulphur, occasionally with traces of iron, indicate copper-sulphide residues trapped during smelting. These sulphide inclusions are particularly evocative, because they are consistent with the processing of sulphidic copper ores, or possibly the co-smelting of sulphidic and oxidic ores, a technique documented on the Iranian Plateau as early as the third millennium BCE. However, the authors caution that oxide inclusions can also form innocently during melting and casting, when dissolved oxygen segregates as the metal solidifies, so inclusions alone cannot identify the original ore type.

The etched microstructures revealed the hands of skilled smiths. All twelve artefacts show annealing twins, the microscopic signature of repeated cycles of heating and hammering after initial casting, and some preserve slip lines indicating a final cold-working pass without subsequent annealing. Finer grain sizes in certain objects betray more numerous thermo-mechanical cycles, suggesting that the number of working and annealing rounds varied from piece to piece depending on the desired form and finish. Together with tin-rich eutectoid phases and tiny lead-rich globules scattered through some samples, these features paint a picture of sophisticated workshop practice in which casting was only the first step in a deliberate sequence of shaping and heat treatment.

The slag fragments, the waste products of high-temperature chemistry, proved equally informative. Their glassy matrices are consistently fayalitic iron-silicate glasses, laced with magnetite crystals and small droplets of metallic copper that never managed to coalesce and settle into the ingot. By plotting the glass compositions onto ternary phase diagrams, the team estimated the apparent liquidus temperatures of the melts. One sample plots near the fayalite eutectic at roughly 1150 to 1250 degrees Celsius, a technologically realistic smelting range, while the others fall into fields corresponding to seemingly impossible temperatures of 1400 to 1650 degrees. The researchers resolve this paradox elegantly: the high-silica compositions reflect fractional crystallisation during cooling, not superheated furnaces. As fayalite crystals grew, the residual liquid became progressively enriched in silica and alumina, so the final frozen glass records the end point of solidification rather than the peak furnace temperature.

Perhaps the most tantalising findings concern the slags’ chemistry. Several samples contain barium oxide, and the copper prills trapped within the slags carry consistent traces of arsenic, up to 6.5 percent in one case, hinting at the smelting of arsenic-bearing copper ores. Notably, none of the copper prills contain any tin whatsoever. This is a crucial clue: the slags record the smelting of plain copper, yet tin bronzes exist among the artefacts. The most likely explanation is that alloying happened as a separate, later step, possibly through cementation, in which copper metal was mixed with tin or tin-rich material in a crucible, a process previously demonstrated at the Elamite site of Haft Tappeh in southwestern Iran. Alternatively, some bronze objects may have been manufactured elsewhere and imported to Sagzabad as finished goods, though the current data cannot distinguish between these scenarios.

Lead isotope analysis added a geographic dimension, and a puzzle. The twelve artefacts display markedly heterogeneous isotopic signatures, forming a broad linear trend that suggests the copper derived from multiple ore sources rather than a single mine. When compared against 158 published Iranian ore analyses and 154 archaeological metal analyses, the matches were only partial. A few artefacts overlap with the Veshnaveh deposit, the nearest known ancient copper mine, located about 250 kilometres southeast of Sagzabad and exploited from the early third through the second half of the second millennium BCE. Others align weakly with ores from the Kerman region in the southeast, the Lut Block in the east, or zinc-lead deposits in the Urumieh-Dokhtar zone and the Alborz Magmatic Belt, while several show strong isotopic affinities with artefacts from sites such as Sangtarashan, Baba Jilan and Tappeh Sarm. Most samples, however, match no known source cleanly.

The geochemical circumstantial evidence does lend some weight to a Veshnaveh connection. The Sagzabad slags resemble Veshnaveh ores in composition, and both the slags and the ores share a distinctive barium signature, with barite heterogeneously distributed in the deposit. The ore fragment analysed in the study, a piece of chalcopyrite surrounded by oxidised copper and iron minerals, is also geochemically compatible with Veshnaveh material. Still, the absence of isotope data for the slags and the ore fragment prevents the researchers from formally testing whether the smelting debris and the artefacts share a common origin, and the isotopic spread of the artefacts points toward a supply network drawing on both nearby and distant deposits, potentially through long-distance trade in ingots or finished metal.

Set in its regional context, Sagzabad fits neatly into a broader second-millennium BCE pattern across the Iranian Plateau, where unalloyed copper, arsenical copper and tin bronze coexisted in varying proportions. Arsenical copper dominates in the east, at sites such as Tappeh Yahya and Tappeh Hissar, while tin bronze prevails in the centre, north and west, reaching its apogee in the spectacular castings of Iron Age Luristan. The Sagzabad assemblage, with its mixture of plain copper and low-tin bronze, its evidence for sulphide-ore smelting, and its isotopically diverse metal supply, adds a crucial data point from a region that has long stood in the shadow of better-studied western and eastern Iranian metallurgical centres. The authors emphasise that these are preliminary results from a small and unevenly distributed sample, and that a larger assemblage, together with isotopic analysis of the slags and ores, will be needed to establish whether the observed patterns reflect genuine chronological change in alloying practice, the organisation of production, or the exchange networks that moved raw metal across the plateau. What is already clear, however, is that the smiths of Sagzabad commanded a sophisticated, multi-stage metallurgical technology, and that the copper flowing through their hands came from more corners of ancient Iran than anyone had suspected.

Subject of Research: Second-millennium BCE copper-based metallurgy and ore provenance at the Late Bronze Age and Iron Age site of Sagzabad, north-central Iran

Article Title: Archaeometallurgical evidence from Sagzabad in regional perspective: preliminary insights into second-millennium BCE copper-based metallurgy in North-Central Iran

Article References: Archaeometallurgical evidence from Sagzabad in regional perspective: preliminary insights into second-millennium BCE copper-based metallurgy in North-Central Iran. (n.d.). https://doi.org/10.1007/s12520-026-02570-x

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02570-x

Keywords: archaeometallurgy, Sagzabad, Qazvin Plain, Iranian Plateau, Late Bronze Age, Iron Age, tin bronze, copper smelting, lead isotope analysis, slag analysis, Veshnaveh, ancient mining

Panlongcheng, located in present-day Hubei Province near modern Wuhan, flourished during the Erligang period of the Early Shang dynasty, roughly the sixteenth to fourteenth centuries BCE. Archaeologists have recovered more than 500 bronze artifacts from the site, ranging from ritual vessels and weapons to tools and ornaments. Yet before this new investigation, fewer than one-tenth of those objects had ever been subjected to laboratory analysis, and the samples that had been studied came overwhelmingly from the later phases of the occupation. That gap left the earliest chapters of the site’s metallurgical history essentially blank, and it meant that any claims about how Panlongcheng fit into the Shang bronze economy rested on a thin and potentially biased evidentiary base.

The research team, led by Tianyuan Yu of the Henan Museum and the University of Science and Technology of China, together with colleagues including Zhengyao Jin, tackled the problem by analyzing 21 bronze samples that span Phases III through VII of the site’s occupation, extending the analytical record back into periods that had never been sampled before. The researchers deployed a battery of complementary techniques, each of which interrogates a different aspect of the metal. Portable X-ray fluorescence, or pXRF, provided rapid, non-destructive measurements of the elemental composition of the alloys, revealing the proportions of copper, tin, and lead that the ancient founders had combined. Metallographic microscopy, in which polished cross-sections of the metal are examined under high magnification, exposed the crystalline microstructure of the bronze, a kind of metallurgical fingerprint that records how the metal was cast, worked, and reheated.

The third and perhaps most powerful technique was lead isotope analysis. Because lead ores from different geological deposits carry distinctive ratios of the isotopes lead-204, lead-206, lead-207, and lead-208, the isotopic signature of a bronze object can act as a geochemical passport, pointing toward the mines and smelting regions that supplied its raw material. By comparing the isotopic ratios of the Panlongcheng bronzes with published data from other Shang sites, including the royal capital at Zhengzhou, the team could test whether the metal circulating at the frontier came from the same ore sources as the metal used at the center, or whether the outpost drew on separate, more local supply lines.

The results delivered several surprises. First, the metallographic evidence confirmed that bronze tools at the site were remelted and recast, a practice that speaks to the practical realities of life at a remote outpost. Rather than discarding broken implements and waiting for fresh metal to arrive from distant sources, the inhabitants of Panlongcheng recycled their worn tools, feeding old bronze back into the crucible to produce new objects. This kind of secondary casting leaves characteristic traces in the microstructure of the metal, and its confirmation at Panlongcheng provides rare, direct evidence of on-site metallurgical activity at a Shang frontier settlement, complementing earlier discoveries of casting remains in the Xiaozui area of the site.

Second, the compositional analysis showed that high-lead bronzes appear more frequently at Panlongcheng than among the bronzes excavated from the Zhengzhou region, where the Shang royal capital was located. Lead was deliberately added to copper-tin alloys in early Chinese metallurgy to improve the fluidity of the molten metal and to enhance the crispness of cast details, a quality especially prized in the elaborate ritual vessels of the Shang elite. The higher incidence of leaded alloys at the frontier site raises intriguing questions about local casting preferences, the availability of lead metal in the southern regions, or perhaps the kinds of objects being produced there. Whatever the explanation, the pattern marks Panlongcheng as metallurgically distinctive in at least one respect.

Yet the third major finding cuts against any picture of the outpost as an isolated or semi-independent metallurgical center. When the researchers compared alloy types and lead isotope signatures across the two regions, the bronzes from Panlongcheng and Zhengzhou turned out to share more similarities than differences. The same broad range of alloy recipes appears at both sites, and the isotopic data point to common or overlapping sources of metal raw material. In other words, the bronze that flowed through the frontier outpost was drawn from the same metal supply system that fed the royal capital, even if the frontier communities exercised some local variation in how they used it.

The authors interpret this combination of shared resources and local variation through the lens of what they call the resource-political framework of the early Shang polity. On this view, the Shang state did not simply extract raw materials from conquered or colonized territories; it constructed an integrated system in which peripheral regions like the middle Yangtze, rich in copper and other ores, were linked to the political core through administrative and military infrastructure. Panlongcheng, strategically positioned to control access to the metal-bearing regions of the south, functioned as a hub in that system, acquiring metal resources from the surrounding periphery and channeling them into networks that ultimately connected to Zhengzhou. The outpost’s bronzes, on this reading, are the material residue of a political economy that made core and periphery mutually dependent.

The study also carries broader implications for how archaeologists understand the emergence of bronze civilization in China. The Erligang expansion into the Yangtze valley has often been framed as a one-way projection of power from the Central Plains, with the south serving as a passive source of raw wealth. The new data complicate that narrative. If the founders and metalworkers at Panlongcheng were working within the same alloy traditions and drawing on the same ore sources as their counterparts at the capital, while also developing local practices such as more frequent lead alloying and systematic tool recycling, then the frontier was not merely an appendage of the core. It was a place where the technologies and resource systems of the Shang state were actively reproduced, adapted, and sustained, contributing to the broader development of bronze casting technology in the region.

Methodologically, the work demonstrates the value of combining multiple analytical techniques on a single assemblage, and of extending sampling into under-studied phases of a site’s occupation. Each method on its own would have told only part of the story: pXRF alone could not distinguish remelted metal from freshly cast metal, and isotope ratios alone could not reveal how objects were made. Together, the techniques build a layered account of production, circulation, and use that no single measurement could achieve. With more than 90 percent of Panlongcheng’s bronze assemblage still unanalyzed, the 21 samples examined here represent a beginning rather than an end, and future work will test whether the patterns identified in this study hold across the full range of the site’s remarkable corpus. For now, the findings stand as a vivid reminder that the great bronze age of China was knit together not by isolated centers and passive hinterlands, but by a web of connections in which even the most distant outposts participated fully in the metallurgical life of the early Shang state.

Subject of Research: Archaeometric analysis of Early Shang dynasty bronze artifacts from the Panlongcheng site in China

Article Title: Periphery and core: insights from the scientific analysis of bronzes from Panlongcheng

Article References: Yu, T., Fan, A., Zhang, C., Huang, F., & Jin, Z. (2026). Periphery and core: insights from the scientific analysis of bronzes from Panlongcheng. Archaeological and Anthropological Sciences, 18(10), Article 210. https://doi.org/10.1007/s12520-026-02568-5

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02568-5

Keywords: Panlongcheng, Early Shang dynasty, bronze metallurgy, lead isotope analysis, pXRF, metallography, Zhengzhou, Erligang period, archaeometry, Yangtze River, metal provenance, resource-political framework