An exceptional microsample from the ground layer of Leonardo da Vinci's Mona Lisa was analyzed by high-angular resolution synchrotron X-ray diffraction and micro Fourier transform infrared spectroscopy, revealing a singular mixture of strongly saponified oil with high lead content and a cerussite (PbCO3)-depleted lead white pigment. The most remarkable signature in the sample is the presence of plumbonacrite (Pb5(CO3)3O(OH)2), a rare compound that is stable only in an alkaline environment. Leonardo probably endeavored to prepare a thick paint suitable for covering the wooden panel of the Mona Lisa by treating the oil with a high load of lead II oxide, PbO. The review of Leonardo's manuscripts (original and latter translation) to track the mention of PbO gives ambiguous information. Conversely, the analysis of fragments from the Last Supper confirms that not only PbO was part of Leonardo's palette, through the detection of both litharge (α-PbO) and massicot (β-PbO) but also plumbonacrite and shannonite (Pb2OCO3), the latter phase being detected for the first time in a historical painting.

The Night Watch, painted in 1642 and on view in the Rijksmuseum in Amsterdam, is considered Rembrandt's most famous work. X-ray powder diffraction (XRPD) mapping at multiple length scales revealed the unusual presence of lead(II) formate, Pb(HCOO)2, in several areas of the painting. Until now, this compound was never reported in historical oil paints. In order to get insights into this phenomenon, one possible chemical pathway was explored thanks to the preparation and micro-analysis of model oil paint media prepared by heating linseed oil and lead(II) oxide (PbO) drier as described in 17th century recipes. Synchrotron radiation based micro-XRPD (SR-µ-XRPD) and infrared microscopy were combined to identify and map at the micro-scale various neo-formed lead-based compounds in these model samples. Both lead(II) formate and lead(II) formate hydroxide Pb(HCOO)(OH) were detected and mapped, providing new clues regarding the reactivity of lead driers in oil matrices in historical paintings.

3 Technical RepoRT New Opportunities Offered by the ESRF to the Cultural and Natural Heritage Communities Marine Cotte,1,2 Kathleen DollMan,1 VinCent FernanDez,1 ViCtor Gonzalez,3 FreDeriK VanMeert,4,5 letizia MoniCo,6,7,4 Catherine Dejoie,1 ManFreD BurGhaMMer,1 loïC huDer,1 Stuart FiSher,1 Wout De nolF,1 iDa FazliC,1,8 hiraM CaStillo-MiChel,1 Murielle SaloMé,1 Marta GhirarDello,9 Daniela CoMelli,9 oliVier Mathon,1 anD Paul taFForeau1 1European Synchrotron Radiation Facility (ESRF), Grenoble, France 2Sorbonne Université, CNRS, Laboratoire d’Archéologie Moléculaire et Structurale (LAMS), Paris, France 3Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, Gif-sur-Yvette, France 4Antwerp X-ray Imaging and Spectroscopy Laboratory (AXIS) Research Group, NANOLab Centre of Excellence, University of Antwerp, Antwerp, Belgium 5Paintings Laboratory, Royal Institute for Cultural Heritage (KIK-IRPA), Brussels, Belgium 6CNR-SCITEC, Perugia, Italy 7Centre of Excellence SMAArt, University of Perugia, Perugia, Italy 8Science Department, Rijksmuseum, Amsterdam, The Netherlands 9Physics Department, Politecnico di Milano, Milano, Italy Introduction For the past 20 years, the community of heritage scientists has frequently exploited the synchrotron radiation-based techniques offered at the European Synchrotron Radiation Facility (ESRF), Grenoble, France [1]. X-ray imaging techniques (in particular, micro computedtomography, μCT) are regularly employed to probe non-destructively the inner structure of objects and materials. In paleontology, this can offer information on the functioning and evolution of organs and organisms. In addition, analytical techniques such as X-ray fluorescence (XRF), X-ray powder diffraction (XRPD), and X-ray absorption spectroscopy (XAS) are often used, alone or combined, for the chemical analysis of micro-fragments of historical manufactured materials. This can give clues about both the early days of objects (physical and chemical processes used in the production of artworks and the evolution of these skills in time and space) as well as the evolution/alteration of objects (nature of degradation products and environmental factors contributing to these degradations). The limited size of samples and their high heterogeneity often require access to micro and nano-probes. The new capabilities offered by the ESRF upgrade “EBS” (Extremely Brilliant Source), as well as instrumental developments at new and strongly refurbished beamlines, have motivated the organization of a dedicated “EBS-workshop” about cultural and natural heritage, which was held in January 2020 at the ESRF, attracting more than 150 participants, among which were 90 new ESRF users. Most of the talks were broadcast on the ESRF YouTube Channel and are still available (https:// youtube.com/playlist?list=PLsWatK2_NAmyyA0n03OMJMAKobVIvow2D). Through scientific presentations, tutorials, and discussions, the objectives of the workshop were: 1. To illustrate to expert and non-expert users the many capabilities offered by synchrotron radiation-based techniques for the study of natural and cultural heritage materials/objects; 2. To present EBS and the related instrumental developments, highlighting the ground-breaking capabilities that will be offered through the ESRF upgrade phase 2 (thanks to the new source, new beamlines, and new instruments); 3. To present and discuss the upstream and downstream challenges associated with these new instruments (e.g., access models and data analysis, data management...), which are fundamental for making the experiments a success. This was notably a very good opportunity to discuss the implementation of new beamtime access modes.

The European Synchrotron Radiation Facility (ESRF) has recently commissioned the new Extremely Brilliant Source (EBS). The gain in brightness as well as the continuous development of beamline instruments boosts the beamline performances, in particular in terms of accelerated data acquisition. This has motivated the development of new access modes as an alternative to standard proposals for access to beamtime, in particular via the “block allocation group” (BAG) mode. Here, we present the recently implemented “historical materials BAG”: a community proposal giving to 10 European institutes the opportunity for guaranteed beamtime at two X-ray powder diffraction (XRPD) beamlines—ID13, for 2D high lateral resolution XRPD mapping, and ID22 for high angular resolution XRPD bulk analyses—with a particular focus on applications to cultural heritage. The capabilities offered by these instruments, the specific hardware and software developments to facilitate and speed-up data acquisition and data processing are detailed, and the first results from this new access are illustrated with recent applications to pigments, paintings, ceramics and wood.