The characterization of Sn‐based corrosion products in ancient bronzes: a Raman approach

Abstract

The characterization of corrosion patinas on bronzes is preliminarily connected to the determination of proper conservation strategies. Moreover, it also provides an essential contribution to the comprehension of the mechanisms of formation of patinas.Concerning the last aspect, several studies highlighted that bronze corrosion behaviour cannot be assimilated to that of pure copper. In particular, decuprification and relative enrichment of tin in the corrosion layers were observed. Tin therefore, together with its insoluble salts, plays an important role in the mechanism of formation of bronze patinas. Thus, the characterization of Sn-based corrosion products becomes fundamental, although remaining quite problematic. This work reports several case studies where Sn-based corrosion products grown in bronzes have been identified, thanks to the hyphenated system scanning electron microscopy-energy dispersive spectrometry-Raman structural and chemical analyser. Combining the main characteristics of these techniques, different Sn-containing compounds, mainly crystalline and nanosized tin dioxides, were detected in bronze patinas exposed to different environments (to the atmosphere, in both natural and accelerated ageing conditions, and to the soil). The main issues regarding the interpretation of Raman spectra of these compounds are presented and discussed.

Raman spectroscopy characterization of 10‐cash productions from the late Chinese emperors to the Republic

“…Due to its sensitivity and noninvasive character, Raman spectroscopy is being increasingly used in the study of artistic and archaeological objects . In particular, Raman spectroscopy has been used for identifying corrosion products in copper/bronze and other metals and characterizing artistic patinas produced in copper‐base alloys …”

Gold in the Alhambra: study of materials, technologies, and decay processes on decorative gilded plasterwork

“…Finally, Raman spectroscopy appears as one of the most suited methods to investigate cultural heritage materials because of its unique advantages, particularly the invaluable ability to analyze the objects in a completely noncontact and nondestructive way . In the last years, this technique has been demonstrated to be very useful to identify not only the materials intentionally used by the artists but also several decay products from pigments and metals in works of art . In this way, by combining the results provided by several microanalytical techniques applied in a nondestructive way on the same microsamples, we will maximize the information that can be obtained from the gildings minimizing the impact on the artwork.…”

Surface investigation of naturally corroded gilded copper-based objects

“…the difference in the electrochemical potential of the metals, the presence and nature of the electrolyte and the microchemical structure and the metallurgical features of the metallic substrate and of the noble metal layer. These factors can cause different chemical and structural transformations in the artefact giving rise to the formation of a wide panorama range of possible mineral species [4,8,[10][11][12]. The BSE image of Figure 2 shows that the thickness of the gilded layer is less than 10 μm, as often observed by other authors in Roman and Barbarians artefacts [1,[14][15] and EDS analyses do not detect the presence of Au and Hg in the substrate under the gilded layer thus excluding the occurrence of an Au-Cu inter-diffusion phenomenon, as instead which has been observed by other authors [23].…”