Probing Works of Art with Photons and Charged Particles

Abstract

The Centre for research and restoration of the museums of France (C2RMF), located in the Louvre palace in Paris routinely uses advanced scientific methods for the study of objects of cultural heritage. Among these techniques, those based on photons or ion beams meet the harmless character required for the study of these invaluable artefacts. The first step of the investigation, namely the examination is advantageously achieved with X-ray, ultraviolet and infrared imaging. Secondly, chemical and structural characterization of materials constituting the objects are performed using a large panel of analytical methods. The chemical composition is delivered either by X-ray fluorescence or by ion beam methods such as particle induced X-ray emission (PIXE) and particle induced γ-ray emission (PIGE) with the 3-MeV proton beam produced by the AGLAE electrostatic accelerator facility of the Centre. As far as the structure is concerned, it is obtained by X-ray diffraction or by μ-Raman spectrometry. These non destructive, non-invasive, rapid and sensitive analytical methods enable to answer three major issues in the field of Art and Archaeology: 1) identification of the material, 2) determination of the provenance and 3) study of surface modification (ageing, alteration). Selected case studies performed at the Centre illustrate the benefits of these methods. For instance, underlying compositions and artists’ signatures are revealed by X-rays in painted masterpieces, while the gemstones mounted on Medieval jewels are characterized by PIXE and μ-Raman spectrometry. The provenance of the pyraldine garnets (X₃Al₂Si₃O₁₂, X=Fe, Mg, Mn) determined by the composition and by identification of microscopic inclusions yields an historical implication to the evolution of gems routes during the Dark ages. As a conclusion, new trends in the use of non-destructive techniques in Art and Archaeology are presented.