Corrosion assessment of a bronze equestrian statue exposed to urban environment

This paper presents the characterization of the conservation state of a bronze equestrian statue exposed outdoor, through an in-situ, multi-analytical, and non-invasive approach. The artefact under study is a bronze equestrian statue, devoted to Alfonso La Marmora, placed in an urban environment in the city of Turin. The investigation was carried out in the framework of a restoration intervention, with the principal aim of characterizing the overall conservation state of the sculpture to provide the conservators with information useful to develop a tailored restoration plan. X-ray fluorescence spectroscopy (XRF) was carried out for the identification of the elements present in the artefact alloy, showing that the statue was made using mainly two bronze alloys. Electrochemical Impedance Spectroscopy (EIS) was performed to study the corrosion mechanisms and to define the protective effectiveness of the patina present on the surfaces. Eventually, Raman spectroscopy (RS) was performed to characterize the chemistry and microstructure of the corrosion products, mainly identified as sulphates. The combination of these techniques allowed to confirm the presence of wax layers from previous restoration work, still capable to protect the metal substrate against corrosion. In addition, it was possible to correlate the conservation state to the exposure conditions and location on the statue.