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HIGH TIN AND TINNED COPPER-BASED ARTEFACTS FROM ANCIENT ABRUZZO

(CENTRAL ITALY, VIII-V CEN. BC)

Ingo Gabriel M.

1

, Riccucci Cristina

1

, Albini Monica

1

, Angelini Emma

2

, Grassini Sabrina

2

,

Faraldi Federica

2

, Faustoferri Amalia

3

, Lapenna Alessandra

3

, Pierigè Isabella

3

1

CNR-ISMN, Montelibretti, Rome, Italy, [email protected]

,

2

Dipartimento di Scienza dei Materiali ed Ingegneria Chimica Politecnico di Torino, Turin, Italy;

Beni Archeologici dell’Abruzzo, Via dei Tintori 1, 66100 Chieti, Italy

3

Soprintendenza per i

Selected groups of copper-based artefacts found during archaeological excavations of different sites of Abruzzo (central Italy) were investigated in order to determine the chemical composition and metallurgical features of the alloys and the micro-chemical and micro-structural nature of the corrosion products grown during the long-term burial. The investigated Cu-based artefacts were ornamental objects such as rivets, buckles, belts and small rings. The analytical characterisation was performed by using different surface and bulk techniques, such as optical microscopy (OM), scanning electron microscopy coupled with energy dispersive X-ray micro-analysis (SEM-EDS) and X-ray diffraction (XRD). The results have evidenced that the bronze artefacts were produced by casting unusual high-tin bronze alloys in a ceramic bivalve mould or by using a low tin bronze alloy coated with a thin layer of tin for producing a silver-like appearance. The main alloying elements were corroded to form different stratified structures of different chemical species, such as tin oxides (romarkite and cassiterite), cuprous oxide and copper carbonates (azurite and malachite), dangerous chlorine-based compounds (nantokite and atacamite polymorphs). This evidenced the strict interaction with the soil components and pH variation, as well as the occurrence of post-burial degradation phenomena. These results confirm that SEM-EDS, XRD and

OM can be successfully used for studying the corrosion products of archaeological copper-based artefacts in order to identify the corrosion agents and mechanisms and, thereafter, to propose the best reliable tailored strategies for the conservation of these ancient artworks.

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