Analytical characterization of corrosion products of copper and its alloys on stained stone surfaces

Monuments, where stone and metals or metallic alloys are used together, are very frequently met in all historical periods and in all countries. In the case of bronze and other copper alloys, their corrosion products can be dissolved by the action of acid rain and thus reach the porous building materials in contact with (or near to) the metallic structures. Once absorbed by the stone, they precipitate on the external stone surface and inside its porous space. As the majority of these products are coloured, their precipitates may produce stains, which are perceived as unpleasant alterations of the original ‘values’ of the stone monuments. The removal of stains is therefore required on the occasion of conservation treatments. The paper reports on the characterisation of copper corrosion products found on two, very different, monuments in Rome: ‘Fontana delle Tartarughe’ (by T. Landini, last quarter of the 16th century) and ‘Statua dello Studente’ (by A. Cataldi, 1920). To identify the speciation of copper compounds in their carbonate matrices, different techniques [X‐ray diffraction, X‐ray fluorescence, SEM/energy‐dispersive X‐ray spectroscopy (EDS), micro‐Raman and XPS] had to be employed. To further confirm the identification of the chemical species, SEM/EDS data were also processed by principal component analysis. Copyright © 2013 John Wiley & Sons, Ltd.