Conserving a Monumental Bronze: The Emperor Tiberius

This 1st-century CE bronze statue of Emperor Tiberius was in need of treatment to address structural stability issues that had rendered the statue unsafe for display. This presented a rare opportunity to investigate the technology and methods used in antiquity to produce such a large-scale bronze, as well as to interpret the statue’s condition at its time of recovery in the 18th century and the impact on the statue’s subsequent historic restorations. By better understanding the various histories inherent in this object, the nature of the issues affecting its stability could be identified and a suitable treatment developed to allow the sculpture to be returned safely to view.

• Structurally stabilized the sculpture
• Responsibly cleaned the surface to respect both its ancient and historic properties to aesthetically integrate the composition and make the object more presentable
• Analyzed the materials and techniques of ancient manufacture
• Analyzed and identified alteration through burial and the impact on restorations
• Analyzed and identified the materials and techniques associated with historic restorations
• Displayed in the exhibition Tiberius: Portrait of an Emperor (Getty Villa, October 16, 2013–March 3,, 2014)

Discovery

Archival evidence indicates that the bronze Tiberius was discovered on August 30, 1741 in Herculaneum. Recent studies of the 18th-century excavations reveal that the statue was unearthed in the area of the Porticus, where a nearby inscription believed to belong to the statue would date it to AD 36 or 37. Accordingly, the portrait would have stood for 42 years until it was buried by volcanic eruption of Vesuvius in AD 79.

Ancient Manufacture

Ancient large-scale bronzes were often built from a number of composed and assembled parts. This feature is well-attested in other ancient bronzes and fully expected in a sculpture this size, as it stands over eight feet tall. But to our surprise the Tiberius was found to be assembled from an unprecedented 62 separate bronze parts. The great number of individual fragments appears to give further insight into working practice, whereby consideration of joining between separately cast fragments was a significant factor.

18th-Century Repairs

A fair amount of archival information has survived regarding the restoration of Tiberius in the 1700s. The statue was cleaned with abrasive materials such as rasps, files, and possibly acids. The left hand was reattached, and other missing sections were repaired, recast, and pinned for added security. The right arm does not seem to be original to the statue and thus also a restoration. A patina was added by applying and heating oxidizing solutions. Finally, small areas were filled with a dark putty containing corrosion products that most likely had been removed from the statue’s surface during cleaning.

Methodology

A variety of techniques were used to study and analyze the sculpture, including examination under magnification and with varying light sources such as visible, ultraviolet (UV) and Infrared (IR), X-radiography, endoscopy, combined X-ray fluorescence and X-ray diffraction. Our primary goal was to structurally stabilize the statue so that it could be stood upright, allowing it to return to display. This involved the identification of the chemical/physical nature of the ancient bronze itself and any and all restorations, their original state and any subsequent alterations to better predict their behavior going forward. How these materials interacted, whether metallurgically (welded), mechanically (bolted), or both also had to be defined. Lastly, how the assembly could feasibly be attached to the display furniture also had to be considered.

Stabilization

The multiple fragments that comprised the sections of the toga were found to be stable but, given the immense size and weight of the statue, needed additional reinforcement to ensure long-term structural stability. We envisioned a centralized structural member to which all sections could be secured and that would help to channel the considerable weight of the bronze down to the ankles and feet. This would also create a bridging element that would connect separate sections, augmenting and reinforcing the ancient joins by establishing new connections to help the statue better respond to the constant force of gravity and any other external forces.

The major difficulty in implementing any form of reinforcement was access to the hollow interior, with the only point of ingress being the narrow, limited space between the feet. Several designs were created and tested. Ultimately a square-sectioned aluminum post was selected which had geared expandable/retractable conformal cleats placed along its length in correspondence with the relative location of the section to be secured. Each cleat could be activated by its individual gearing via a long hexagonal wrench inserted up the hollow of the post. Seven separate sections were each secured to the central post, which was lastly secured to the ankles just inside the hollow of the interior where it would not be visible.

Study

The conservation process allowed us the chance to study Tiberius in detail to identify some of the methods used by 18th-century restorers. One of the areas for further research is to uncover the techniques and chemicals used to create the greenish-black surface of the artificial patina.

Cleaning

Because a key aspect of our conservation project was cleaning the figure, it became necessary to understand what had happened to the statue’s surface over the centuries. This ensured that we treated it correctly (the cleaning is, after all, the only aspect of our work that isn’t reversible).

Erik Risser, Conservator, Antiquities Conservation

National Archaeological Museum in Naples (Museo Archeologico Nazionale di Napoli)