A recent study of an ancient Mesopotamian sculpture using cutting-edge technology has provided information about the earliest metal casting techniques in human history, revealing the technical challenges faced by artisans more than 4,000 years ago. The research, published in the journal Heritage Science, focused on the “Head of a Ruler“, an impressive copper piece that is part of the collection at the Metropolitan Museum of Art in New York, and has recently been attributed to the Akkadian period of Mesopotamia, which developed between 2350 and 2150 B.C.

The team of researchers, led by J.-F. de Lapérouse of the Metropolitan Museum of Art, employed an advanced high-energy X-ray computed tomography technique to thoroughly examine the internal structure of the sculpture. This non-invasive method, carried out at the X-ray Analysis Center of the Swiss Federal Laboratories for Materials Science and Technology (Empa), allowed scientists to obtain an unprecedented three-dimensional view of the ancient work of art, revealing details about its creation process and the difficulties its creators faced.

The “Head of a Ruler“, which represents a bearded man with an elaborate braided hairstyle and interwoven ribbons, probably Rimush I of Akkad (second king of the Akkadian Empire and son of Sargon and his consort Tashlultum), is considered one of the earliest life-sized sculptures made using the hollow-core lost-wax casting technique. This technological innovation, which emerged in Mesopotamia during the third millennium B.C., marked a milestone in the history of metallurgy, allowing for the creation of larger and more naturalistic sculptures than was possible with earlier methods.

Bust of Sargon of Akkad
Bust of Sargon of Akkad. Credit: Public domain / Wikimedia Commons

The tomographic analysis revealed that the sculpture has surprisingly thick metal walls in the front, measuring between 30 and 37 millimeters, while the back is considerably thinner, with a thickness of about 6 millimeters. This uneven distribution of metal undoubtedly posed a significant challenge for the casters of the time, who had to deal with issues related to the uneven solidification of the metal and the formation of trapped gas bubbles.

One of the most intriguing findings was the presence of six large core supports, essentially conical pegs with a square cross-section, which were inserted through the wax and into the clay core during the casting process. These supports, measuring between 23 and 26 millimeters in length, played a crucial role in holding the core in place during casting, but also presented their own technical challenges.

Comparison with another contemporary sculpture, the so-called “Head of Sargon” from the Iraq Museum, revealed significant differences in production techniques. While the “Head of Sargon” shows a more uniform wall thickness and uses pairs of smaller core supports, the Metropolitan Museum’s “Head of a Ruler” presents a more complex and technically risky structure.

Left: Back of the Head of a ruler seen in natural light; Right: the same in 3D reconstruction
Left: Back of the Head of a ruler seen in natural light; Right: the same in 3D reconstruction. Credit: J-F. de Lapérouse et al.

The study also uncovered several casting defects in the Metropolitan Museum’s sculpture, including a missing section in the beard and a high overall porosity, particularly concentrated in the front of the head. These findings suggest that the Mesopotamian artisans were still in the process of mastering the complexities of large-scale casting, facing challenges such as controlling the metal’s solidification and preventing the formation of gas bubbles.

Particularly interesting was the discovery of an area at the back of the head that appears to have been the result of an ancient repair. The researchers speculate that this spot may have been the site of a significant casting defect that required a second pouring of metal to close the head’s wall.

The researchers conclude that the “Head of a Ruler” appears to have been produced by an artist accustomed to sculpting in solid materials like stone or clay, who either was not fully aware of the specific requirements of metal casting or was collaborating with people with limited casting knowledge.

Despite these technical challenges, the “Head of a Ruler” remains a masterpiece of ancient sculpture. The presence of an intentional line over the left ear, revealed by the scan, has led researchers to suggest that the sculpture may have originally been gilded, adding another layer of complexity and sophistication to its creation.

SOURCES

de Lapérouse, JF., Eppihimer, M., Flisch, A. et al. Revealing ancient technology: a high-energy X-ray computed tomography examination of a Mesopotamian copper alloy head. Herit Sci 12, 307 (2024). doi.org/10.1186/s40494-024-01417-9

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