Bronze Casting

CLAY TO BRONZE

Bronze casting and techniques involved in bronze making – such as mining and smelting of of alloys – reached a high level of sophistication during the Shang dynasty. [1] The creation of bronze weapons, tools, and ritual vessels marked the period development, where changes in material correlated with changes in the function of these objects. Prior to the Shang dynasty, attention was placed on ceramics and pottery. The earliest known earthenware dates back to the preceding late Neolithic period (a speculated prehistoric age to have stretched from approximately 7000 BC to 2000 BC) – which includes pieces deriving from the Yueshi culture and Longshan culture – as well as the Erlitou culture of the supposed Xia dynasty (see map to learn more).[2] These developments in ceramics would influence later bronze making in several way. Firstly, the control and maintenance of the appropriate temperature needed for firing earthenware vessels was crucial to improvements made in creating more durable ceramics necessary for bronze casting.[3] Secondly, as oppose to hammering, or the use of wax molds in the lost-wax casting, the techniques utilised in working with clay were transferred into the piece mold process in Shang bronze ware making and crafting.[4] A distinct difference between the ceramic prototype and the bronze vessel is that the latter would feature more prominent handles.

Late Neolithic ceramic tripod vessel with "udder-shaped" legs characteristic of earthenware of this period [67]

Early Shang bronze li (鬲 )food vessel

Late Shang bronze ding (鼎) vessel

BRONZE CASTING PROCESS

Shang bronzes were cast using the piece mold method, also known as "section mold casting."[5] The process first involved creating a full-sized ceramic prototype of the desired object out of clay, which was then left to dry and harden. Damp clay was then pressed around the object and left to reach a semi-hardened and slightly pliable state – creating what is called a negative mold.[6] Afterwards, the clay was cut into sections and removed from contact with the clay model. These parts were then fired and hardened in a kiln. Furthermore, inscriptions were carved into the hardened clay – such as in the case of the Houmuwu – which would later create relief designs on the object. The clay prototype was shaved down and was situated and held in the middle by bronze spacers as the pieces of the mold were assembled back together around it.[7] It is at this stage that molten bronze is quickly poured in the spaces between the mold and the model and left to cool. These steps demonstrate the level of sophistication and complexity involved in the making of the Houmuwu.

Diagram of the Piece Mold Technique

Diagram of the casting of the Houmuwu

As oppose to hammering or lost-wax casting, methods of smelting and section-mold casting were used in the making of Shang bronzes.

Here is a video from the Minneapolis Institute of Art that not only introduces ancient Chinese bronze ware, but how ink rubbings and line drawings are important to examining the material object itself, particularly the "decoration, design and casting techniques" of a vessel. [8]

HOW ABOUT THE HOUMUWU?

Whilst the ding arguably evolved from the prior designs of ceramic vessels, the fangding (a rectangular ding vessel) was made only in the medium of bronze.[9] Considering its scale and weight, the Houmuwu shows the extent of Shang craftsmanship, as well as advancements in obtaining a considerable amount of raw metal ores and and working with these resources. In addition to the piece mold process, the handles and feet of the vessel are hollow, suggesting the use of the “joining-cast” method.[10] This means that handles and feet were cast separately and was later joined to the body of the vessel. This not only shows how various techniques and processes were implemented in the making of a single object, but the highly sophisticated level of bronze ware making needed to produce a vessel of this magnitude. It reflects not only the degree of advancements in metalwork during the Chinese Bronze Age, but how these methods were already highly developed toward the end of the Shang dynasty, well before the succeeding Zhou dynasty.

Considering the above, the vessel appears as a product of the collective effort and organisation of a large group of workers - especially smelters and casters. While some scholars predicted that it would have involved around 70 to 80 craftsmen, others argue that an 800 kg vessel – one like the Houmuwu – would have required approximately 200 to 300 workers, a number that does not include those needed for the mining of metal ores and the smelting of metal alloys.[11] Thus, the vessel shows the scale of early productive complexity, from the mobilisation of large-scale labour, to mining and smelting, and finally the technique and artistry of metal casting and decoration.

METALLURGY

By examining the metal components of the Houmuwu, it not only provides insight into the level of early bronze development in China, but might tell us about the possible geographic reaches and movements of people from its royal centre – the capital of Yin – during the late Shang dynasty. The bronze alloys of Shang vessels are made of copper and tin with high levels of lead content, for the particular metallurgic makeup of the Houmuwu measures as 84.77% copper, 11.64% tin, 2.79% lead.[12] According to Elizabeth Childs-Johnson, the bronze used in Shang vessels derive from a number of ore mines in southern China, that it is likely sourced from the abundant copper mines in Yunnan, approximately 2000 kilometers south of the Shang capital of Yin in Henan.[13] Along with with the support of Zhengyao Jin’s research, Childs-Johnson arrives at this conclusion based on matching the same level of “highly radiogenic” lead in these reserves, with those found in numerous early Shang bronze vessels.[14] Other scholars, like Wei-dong Sun, also postulate that they most likely travelled far south to obtain tin, since there is no tin deposits within a 1000 km radius of the Yin capital.[15]

An extensive study recently published in the Scientific Reports in 2016 explains a striking similarity between the "puzzlingly high lead isotopic compositions " in Yin-Shang bronze ware and the levels of lead molecules measured in African copper.[16] Although this is a speculation and research on the metallurgic components of Shang bronzes continue to be conducted, it shows for now the possibility of trade across extensive distances that perhaps may have occurred already in the late Shang dynasty.[17] This sheds light on the possible scale of geographic movement, not just in terms of conquering other states through incursions, but the plausibility that the Shang may have had the means to conduct cross-border trade involving extensive distances of travel and reach.

WANT TO LEARN MORE?

Visit the Freer Gallery of Art and the Arthur M. Sackler Gallery site to find out more about bronze smelting and casting. The site also has links to other aspects of ancient Chinese bronzes, including a slideshow where you can take a closer look at various Shang bronze articles.

Reference:

[1] Behzad Bavarian and Lisa Reiner, Piece Mold, Lost Wax & Composite Casting Techniques of the Chinese Bronze Age, (Los Angeles: California State University Northridge, 2006), i.

[2] Julia M. White and Ronald Y. Otsuka, Pathways to the Afterlife:Early Chinese Art from the Sze Hong Collection, (Honolulu: University of Hawaii Press,1993)15.

[3] Ibid.

[4] Ibid.

[5] Behzad Bavarian and Lisa Reiner, Piece Mold, Lost Wax & Composite Casting Techniques of the Chinese Bronze Age, (Los Angeles: California State University Northridge, 2006), 9.

[6] Rose Kerr, Joseph Needham, and Nigel Wood. Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, ed. Rose Kerr, (Cambridge, Cambridge University Press, 2004), 396.

[7] Ibid.

[8] Minneapolis Institute of Art. "Chinese Bronzes, Of Us and Art: The 100 Videos Project, Episode 19." YouTube video, 2:33. Posted May 26, 2015. https://www.youtube.com/watch?v=m3pvO84KXdE.

[9] Behzad Bavarian, Ceramic’s Influence on Chinese Bronze Development (Los Angeles: California State University Northridge, 2006), 13.

[10] Jian Hang and Qiuhui Guo, Chinese Arts and Craft, trans. Zhu Youruo and Song Peiming (Cambridge: Cambridge University Press, 2012), 51.

[11] Scott L. Montgomery and Alok Kumar, A History of Science in World Cultures: Voices of Knowledge, (London: Routledge), 2015, 175. Jiantang Han, Chinese Characters, trans. Wang Guozhen and Zhou Ling (New York: Cambridge University Press, 2014), 31. Behzad Bavarian, "Piece Mold, Lost Wax & Composite Casting Techniques of the Chinese Bronze Age," i.

[12]Jiang, Yu-Qian, Shu-Xiang Ruan, Shan Tang, and Zhi-Gang Shuai. “Chemistry Progress and Civilization in Ancient China.” Bulletin of the Chinese Academy of Sciences 25, no. 1 (2011): 29.

[13] Elizabeth Childs-Johnson, “Big Ding鼎 and China Power: Divine Authority and Legitimacy,” Asian Perspectives 51, no. 2(2012):169.

[14] Ibid.

[15] Wei-dong Sun, Li-peng Zhang, Jia Guo, Cong-ying Li, Yu-hang Jiang, Robert E. Zartman & Zhao-feng Zhang. "Origin of the mysterious Yin-Shang bronzes in China indicated by lead isotopes," Scientific Reports 6 (2016): 4.

[16]Wei-dong Sun, Li-peng Zhang, Jia Guo, Cong-ying Li, Yu-hang Jiang, Robert E. Zartman & Zhao-feng Zhang. "Origin of the mysterious Yin-Shang bronzes in China indicated by lead isotopes," Scientific Reports 6 (2016): 1.

[17] Ibid., 5.

Images

Header: "The Process of Bronze – Wax Cast and Ceramic Mold." Corbin Bronze. Accessed 25 September, 2017. https://corbinbronze.com/studio/process/foundry/.

"Tripod vessel, li." Compton Verney Art Gallery & Park, Warwick. Accessed 25 September, 2017. http://www.comptonverney.org.uk/cv_collections/tripod-vessel-li/

Early Shang bronze li: "Food Vessel (Li)." The Metropolitan Museum of Art, New York City. Accessed 25 September, 2017.http://metmuseum.org/art/collection/search/61037.

Late Shang bronze ding vessel: "'Ding' Ritual Food Vessel with 'Taotie' Decor: Shang dynasty, c. 1600-c. 1050 BCE." Harvard Art Museums, Massachusetts. Accessed 25 September, 2017. http://www.harvardartmuseums.org/art/204094.

Diagram of the Piece Mold Technique: Edith Watts, "The Great Bronze Age of China: An Exhibition from the People's Republic of China at The Metropolitan Museum of Art, New York," Asia for Educators: Columbia University. Last modified May 22 2009. http://afe.easia.columbia.edu/special/china_4000bce_bronze.htm.

Diagram of the casting of the Houmuwu: Lan-ying Tseng, “Myth, History, and Memory: The Modern Cult of the Simuwu,” in Chinese Culture Centenary, (Taipei: National Museum of History: 1999), 764. Figure 5.

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