Methodological approach in the study of multi-material artefacts by the use of portable X-ray Fluorescence Spectrometry

Obtaining reliable data through portable and non-invasive techniques is often a necessary condition in the study of Cultural Heritage. In fact, this study deals with the methodological approach adopted in the analysis of three reliquaries owned by Musée de Cluny (Paris, France) with which there is a consolidated collaboration. The main characteristic of these important medieval works lies in the variety of the materials they are made of: usually gilded metal decorated with glass, enamels, and gemstones as real pieces of jewellery [1]. Moreover, reliquaries are objects of cult that are sometimes carried in procession and exposed to the touch of the devout and they are often re-arranged over time or have been reproduced in copies. Elemental analysis allows the recognition of authentic parts and remakes and provides very useful information on production techniques and provenance of raw materials. Among other things, it allows comparisons to be made with other products of the same period but of different manufacture. The adoption of X-ray Fluorescence Spectrometry has enabled an accurate characterisation of artefact materials by exclusively non-invasive approach: different measurement conditions have been optimised over time to achieve data comparable with those presented in the literature concerning medieval jewellery [2]. The outcomes are of certain relevance given the lack of systematic diagnostic studies in the scientific literature specifically concerning materials of European late medieval anthropomorphic reliquaries [3]. The combination with optical microscopy allowed a characterisation of the appearance and the colours of the various surfaces investigated. The artefacts are all made of copper gilded with mercury amalgam, but some parts that can be attributed to later additions have been identified. Some elements detected in quantities in the glass are incompatible with medieval production and suggest they may be later substituted. Finally, precious stones as rock crystal, turquoise, zircons, and garnets were identified, in the last case with possible information about their provenance (India or Sri Lanka). [1] Castronovo S. 2020. Bustes reliquaire en orfèvrerie dans le duché de Savoie et dans les territoires voisins (XIIIe-XVe siècles)., Artistes et artisans dans les États de Savoie au Moyen Âge. De l’or au bout des doigts, Silvana Editoriale, Cinisello Balsamo (MI), Italy. [2] Biron I., Dandridge P., Wypyski M.I., 1996, Techniques and materials in Limoges enamels, Enamels of Limoges 1100-1350, Metropolitan Museum of Art, NY [3] Labate M., Aceto M., Castronovo S., Operti L. Agostino A., 2022. Non-invasive analysis of late mediaeval goldsmith’s materials:piedmontese reliquary busts in comparison, Book of Abstracts, JFIC2022, Toulon, France