Corrosion investigation of fire-gilded bronze involving high surface resolution spectroscopic imaging
Gilded bronzes are often affected by severe corrosion, due to defects in the Au layer and Au/Cu alloygalvanic coupling, stimulated by large cathodic area of the gilded layer. Galvanic corrosion, triggered by gilding defects, leads to products growth at the Au/bronze interface, inducing blistering or break-up of the Au layer. In this context, fire-gilded bronze replicas prepared by ancient methods (use of spreadableAu–Hg paste) was specifically characterised by compiling complementary spectroscopic and imaging information before/after accelerated ageing with synthetic rain. Fire-gilded bronze samples were chemically imaged in cross-section at nanometric scale (<200 nm) using high energy and lateral resolution synchrotron radiation photoemission (HR-SRPES) of core levels and valence band after conventional characterisation of the samples by Glow Discharge optical Emission Spectroscopy (GD-OES) and conventional X-ray photoelectron spectroscopy (XPS). We have found a net surface enrichment in Zn and Snafter fire-gilding and presence of metallic Hg, Pb and Cu within the Au layer. Moreover, the composition distribution of the elements together with their oxidation has been determined. It was also revealed that metallic phases including Hg and Pb remain in the gilding after corrosion. Moreover, selective dissolution of Zn and Cu occurs in the crater due to galvanic coupling, which locally induces relative Sn species enrichment (decuprification). The feasibility advantages and disadvantages of chemical imaging using HR-SRPES to study artworks have been investigated on representative replicas.
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Synchrotron radiation; Artworks; Photoemission; Decuprification; XPS; Chemical imaging; Fire gilded bronze; Corrosion; [SPI.MAT]Engineering Sciences [physics]/Materials; [CHIM.MATE]Chemical Sciences/Material chemistry; [SHS.ART]Humanities and Social Sciences/Art and art history; [SHS.ARCHEO]Humanities and Social Sciences/Archaeology and Prehistory
Journal articles; Engineering Sciences [physics]; Chemical Sciences; Humanities and Social Sciences; CNRS - Centre national de la recherche scientifique; TRACES - Travaux et recherches archéologiques sur les Cultures, les Espaces et les Sociétés; Université Toulouse 2; Institut de Chimie du CNRS; Synchrotron Soleil; Ecole des Hautes Etudes en Sciences Sociales; Université Paul Sabatier - Toulouse III