Speaker
Description
From very large, to ultra-small (from meter to manometer); this is how this study of an alteration process on prehistorical cave walls, was dealt. On wall surfaces in some prehistorical caves, a ‘white veil’ has appeared and is being observed quite frequently now. Its origin is not very well defined. For more than 20 years, researchers have been observing and analysing this phenomenon which may contribute to a total degradation of artworks in some of the caves of the Vézère valley in Dordogne, France (UNESCO patrimony). After many campaigns in the fields, a unique cave (the Leye Cave, located in Dordogne, close to the well-known Lascaux cave) has been identified and selected to proceed with all available types of analytical investigations, one of them being the use of Synchrotron radiation (SR). In this specific cave no artwork is present, enabling to proceed to any type of analyses either invasive or not. Thus, the so-called white veil has been defined as composed of 2 types of crystallizations: moonmilk and coralloids. In both cases calcium carbonate crystals have been identified using traditional methods such as optical microscopy, scanning microscopy-energy dispersive X ray spectrometry, X ray fluorescence, Raman spectrometry, Laser-Induced-Breakdown-Spectrometry. At this stage, a deeper study was needed to know more about the crystals through their defects at the atomic and structural level. This is why SR was used thanks to a strong collaboration between the universities of the Region Nouvelle-Aquitaine and the SOLEIL Synchrotron at Saclay near Paris, under a consortium agreement (NACRES project). The objective was to look for potential tracers of the growth mechanisms involved, both from a chemical and crystallographic point of view. Experiments were carried out on three different beamlines combining X-ray diffraction analyses on single crystals (PROXIMA2 beamline), micro-spectrofluorimetry analyses to assess the presence of organic matter (DISCO beamline), and X-ray imaging with a resolution of 150 x 150 nm in order to determine local chemical variations (Nanoscopium beamline). The work presents a synthesis of the results obtained, giving new insights regarding the discussion on the origin of moonmilk (Oral communication to be given by L. Bassel at inArt conference, Paris, 28 June-1 July 2022).