Two turquoise-inlaid bronze plaques with beast mask design from the Erlitou site at Yanshi, Henan Province Photos: Ren Guanhong/CSST

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The emergence and evolution of metallurgical technology marked a watershed moment in the history of early civilization. The transition from the prehistoric era to the age of civilization was signaled by the discovery of metals and the production and use of metal tools. 

A distinctive feature of China’s Bronze Age is the adoption of ceramic mold casting techniques [a piece-mold casting method where molten metal is poured into a ceramic mold, allowing it to take the mold’s shape] to produce bronze ritual vessels. This stands in stark contrast to the metallurgical traditions of West Asia, Central Asia, and Europe, where metals were primarily shaped by forging techniques for weapons, tools, and ornaments, or cast using the lost-wax method [in which a wax model is covered with mold material, then melted away to leave a cavity filled with molten metal. Once solidified, the mold is broken to reveal the final object], typically for sculptures. The Erlitou culture period (c. 1750–1530 BCE) represents a pivotal stage in the formation of this technological system.

  

Large-scale production 

The Erlitou period witnessed the beginnings of large-scale bronze production and the emergence of bronze ritual vessels. According to recent studies, more than 250 copper artifacts have been unearthed at the Erlitou site. Metallurgical remains were mainly discovered in architectural foundations, ash pits, and stratigraphic layers in Areas IV and V of the Erlitou site. In the palace area, 17 copper-related artifacts, including copper slag and ore, were found, while 55 artifacts—including copper slag, crucibles, ladles, ceramic molds, and clay cores—were discovered in the workshop area.  

In the first phase of Erlitou culture, bronze artifacts were scarce, limited to small items like bronze blocks and knives. By the second phase, alongside small tools such as knives and awls, bronze bells and turquoise-inlaid plaques emerged. The third phase saw a marked increase in both variety and quantity, with tools, weapons, and vessels like jue (ritual wine cups), ge (daggers), and qi (halberd-shaped ritual items) appearing. In the fourth phase, the range of vessels expanded to include ding (tripods), he (wine vessels), and gu (goblets). Erlitou bronze vessels typically featured thin walls and simple, single-layered decorations, with ritual vessels predominantly wine-related.

Complex composition 

The bronze artifacts from Erlitou display a range of remarkably complex compositions, encompassing eight types: pure copper, tin bronze, lead-tin bronze, lead bronze, arsenic copper, tin-arsenic copper, lead-arsenic copper, and lead-tin-arsenic copper. This diversity suggests that the effects of adding tin and lead to enhance bronze’s mechanical and casting properties were already understood at that time. Most unearthed vessels were ternary alloys, while tools generally contained higher tin content. However, compared to late Neolithic bronzes and those of the subsequent Erligang culture, the tin content in Erlitou bronzes remained relatively low, reflecting a transitional phase from early metallurgy to a more refined, standardized stage.

From the first to the fourth phase of Erlitou culture, the use of pure copper gradually declined but did not disappear entirely. Arsenic-containing copper also decreased (albeit with some fluctuations), while tin bronze and lead-tin bronze saw increasing use. In the third and fourth phases, lead-tin bronze became widely used, with a significant increase in lead content during the fourth phase, suggesting substantial changes in alloy composition—possibly due to changes in ore sources and smelting techniques.  

During the second and third phases, a single primary ore source dominated, indicating a stable supply before the late Xia Dynasty (c. 2070–1600 BCE). However, in the fourth phase, this source was phased out for a new one, which was later inherited by the Yanshi Shangcheng site [an early Shang (c. 1600–1046 BCE) urban center in the middle Yellow River valley]. As bronze production expanded, demand for raw materials surged, prompting efforts to seek new copper sources. One likely significant source of copper for Erlitou culture bronzes was the Zhongtiao Mountains in southern Shanxi Province.  

A leap in early metallurgical technology  

Due to the complexity of bronze vessel shapes, the composite ceramic mold casting technique [also known as the block mold casting method, an ancient casting technique using reusable multi-piece clay molds] was likely invented specifically for their production. This innovation represents a major leap in early metallurgical technology. Unlike forging, which shapes metal through physical deformation, this technique relied on manipulating metal properties and using sophisticated ceramic molds. Its complexity arose from alloying processes and the interplay between ceramics and casting.

For instance, ceramic mold materials had to be carefully selected and prepared to withstand casting demands. Assembling multiple mold pieces required precise alignment and durability. Many Erlitou molds feature inscribed symbols or mortise-and-tenon structures to aid assembly. Some bronze jue vessels boast walls as thin as 1 mm, highlighting the technical challenge of controlling mold deformation and avoiding defects like porosity.

During the first and second phases of Erlitou culture, simpler artifacts such as bronze knives and plaques could be cast using double-sided molds [a technique employing two-part molds to create symmetrical objects]. Unearthed bronze vessels from the third and fourth phases, such as jue and ding, exhibit complex shapes and uniformly thin walls, demonstrating a notable advancement in casting technology. The jue, the most common among unearthed vessels, was typically cast using two external molds [carefully joined together to create a hollow form] and an internal core between the body and legs [to ensure that the inner cavity of the vessel is properly shaped during casting].  

While Erlitou bronzes generally retained simple forms, often imitating earlier pottery and stone items, they laid the foundation for the structural and aesthetic conventions of Chinese bronzeware. This period saw the establishment of an independent bronze tradition in China, characterized by distinctive vessel shapes and the block mold casting technique. By this stage, core techniques of ceramic mold casting had matured, including vertical and horizontal mold partitioning, precise alignment systems (e.g., marking lines, dowels), and sophisticated mold designs for simple objects. Decorative patterns were pre-carved into the molds before casting, typically arranged in horizontal bands—a hallmark of Chinese bronze production that distinguishes it from Mesopotamian and Egyptian traditions, where decorations were added post-casting.  

During the Erlitou period, techniques such as piece-mold casting and clay-core support [when casting a bronze vessel using a composite mold, both an outer mold and an inner clay core were needed to shape the vessel. To ensure that the clay core stayed properly positioned inside the mold and maintained a uniform wall thickness, small clay supports were inserted between the mold and the core] were already in use. For instance, holes in the belly of certain jue vessels were formed by small protrusions set into the bottom mold. These small protrusions were used to position the bottom mold or the clay core relative to the outer mold and to ensure correct wall thickness, serving the same function as clay core supports.  

Rise of specialized bronze workshops  

Among the nearly 20 bronze plaques unearthed from the Erlitou culture, all feature beast-mask motifs inlaid with turquoise. The intricate and symmetrical designs demonstrate sophisticated inlay craftsmanship. Two decorative approaches are evident: one where the motif is framed by raised bronze lines, with rectangular turquoise pieces arranged in neat rows; and another where the motif is outlined with bands of turquoise inlay, with the turquoise pieces cut into various shapes and arranged into curved, broad bands, forming the beast mask and horns.

Large-scale specialized bronze workshops had already emerged during the Erlitou period. Excavated furnaces suggest an early stage of vertical furnace smelting, with an estimated diameter of 20 cm and a depth of 18 cm. These workshops included casting sites, ceramic kilns for baking molds, and buildings likely used for preheating molds, indicating a high degree of specialization. The site also yielded numerous furnace fragments, ceramic molds, and a single stone mold. Research indicates that the ceramic mold materials used during the Erlitou period were made from washed loess, characterized by a high silt content, low clay content, and a highly porous microstructure—differing significantly from the high-clay-content materials used for pottery making. These findings suggest that the selection of modeling materials and the basic standards and methods for their preparation were already well established during the Erlitou culture period. 

The block mold casting tradition arose from the confluence of cultural and technological exchange, development, and selection. First, the emerging nobility of the Erlitou culture period required bronze vessels as symbols of status and authority, serving both ritualistic and political functions. Second, the expansive loess terrain of the Central Plains provided abundant materials with excellent molding, carving, and refractory properties—ideal for use in bronze casting. Third, since the Neolithic period, the advanced pottery-making tradition enabled artisans to master mold-making, casting, and high-temperature techniques with great skill.

Looking back at the Central Plains four millennia ago, the advent of bronze vessels heralded the birth of China’s Bronze Age ritual and music system. Advanced smelting and casting technologies, coupled with control over metal resources and organized production, laid the material foundation for this cultural framework.

Liu Yu is a research fellow from the Laboratory of Archaeological Sciences and Cultural Heritage Protection at the Chinese Academy of Social Sciences.

Edited by REN GUANHONG