Corrosion of bronze Roman statues

Monitoring the corrosion of 2300 year old bronze Roman statues

The discovery

In 2022, excavations in San Casciano dei Bagni (Italy) uncovered an important complex related to an Etruscan and Roman thermal sanctuary containing a large number of archaeological objects. A votive deposit found within the thermal pool contained Etruscan and Roman bronze statues and ex-votos. This collection, dating from the 3rd century BC to the 1st century AD, represents one of the most intact and remarkable assemblage of bronze artifacts in the Mediterranean and offers an insight into a period marked by significant changes in Etruria during the transition from Etruscan to Roman control. During this turbulent period, characterized by conflicts between Rome and Etruscan cities as well as internal Roman disputes, noble families from both cultures dedicated these statues together in a sanctuary, creating a unique environment of peace amidst widespread political unrest.

In the early 5th century AD, this sanctuary was dismantled and permanently sealed with large tiles, preserving this sacred site in excellent condition to this day.

 

Role of electrochemical investigations

It often happens that metallic artefacts excellently conserved for centuries, undergo severe corrosion processes. upon removal from the site when they are exposed to chemicals commonly present in the atmosphere.

A metal artifact may be covered with artificial or natural patinas which also depend on the exposure conditions, as in the case of this particular thermal context. Unfortunately, these storage conditions did not contribute to the good preservation of the statues and favoured the formation of visibly heterogeneous patinas.

The study of differently corroded areas is of fundamental importance for the design of an appropriate conservation strategy, which must include controlled cleaning interventions and the identification of an optimal level of protection, as well as monitoring the evolution of corrosive processes.

Research on the ongoing corrosion of the found statues has been carried out in the frame of a cooperation between the following institutions:

  • University of Genoa (UNIGE)
  • the Superintendence of Archeology, Cultural Heritage and Landscape of the provinces of Siena, Grosseto, Arezzo (Sabap-Si)
  • the University for Foreigners of Siena (UNISTRASI)
  • the Central Institute for Restoration (ICR)

Method and instruments

The METAL group (Metallurgy in clean Energy, industrial Technologies and Archaeology Labs) of the University of Genoa developed a probe capable of performing in-situ characterization of the patinas by means of electrochemical techniques. Electrochemical Impedance Spectroscopy and Linear Sweep Voltammetry were carried out using the PalmSens4. This device has been chosen for its portability and accuracy allowing us to bring our laboratory techniques on the field and museums, without the need of transferring the statues on purpose. The use of PSTrace software for handling the analysis allowed us to easily manage and interpret the data providing immediate feedback to the restoration experts.

Results

The electrochemical measurements helped determine the restoration action to preserve, clean and stabilize the artefacts. After the intervention and the process of musealization, periodic electrochemical analyses are conducted to evaluate the long-term effectiveness of the preservation strategy.

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PalmSens4 Corrosion package
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