An in situ multi-analytical approach in the restoration of bronze artefacts

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A multi-analytical approach was adopted to compare different cleaning methods during the conservation works on two bronze artefacts: the Brera's Napoleon by A. Canova and the Florence Baptistery's North Door by L. Ghiberti. An appropriate number of surface areas were identified, and their properties and homogeneity were characterised in situ by means of colorimetry, Eddy Current patina thickness measurements, FTIR spectroscopy and electrochemical impedance spectroscopy (EIS). On the Napoleon statue, three sets of laser cleaning parameters were adopted on distinct selected areas. On the North Door, a mechanical and two chemical cleaning methods were applied on two separate areas; both chemical methods were based on Agar gel. The results on surface composition, appearance and corrosion rate of the different cleaning methods were compared with the properties of the uncleaned area with the same set of in situ analytical techniques. Measurements results were statistically analysed to take into account the lack of homogeneity typical of outdoor bronze surfaces.Based on the results obtained on the two bronze artefacts analysed, the role of the analytical techniques adopted is discussed. The effectiveness of the described in situ multi-analytical approach towards a better conservation–restoration methodology for outdoor bronzes is enlightened.