Characterization by XPS and Combined Techniques of (Copper-Based) Coloured Stains Formed on Limestone Surfaces of Outdoor Roman Monuments

Monuments where marble and stone elements are used along with bronze or other copper alloys artefacts such as sculptures, decorations and dedicatory inscriptions are rather frequently met. In outdoor conditions, such a combination implies the corrosion products of the copper based alloy1, directly exposed to rainwater, to be drained off and migrate through the porous surfaces, forming stains of different colours and intensities. In this work we have analysed samples from the limestone surfaces of two modern monuments in Rome, the ‘Vittoriano’ (G.Sacconi, 1885-1911- Piazza Venezia) and the ‘Statua dello Studente’ (A.Cataldi, 1920, La Sapeinza University city) and confirmed, with the aid of XPS and other analytical techniques, that the coloured stains are mainly due to copper and mixed calcium/copper compounds. We have also related the composition of these patches with their chromatic characteristics and with the different sampling location.