Understanding of the alteration mechanism of smalt used in oil paintings using combined Co and K K-edge XRF and XANES spectroscopy

The experiment focuses on the understanding of the alteration mechanism of smalt used in oil paintings between the 15-18th c. First, we want to quantify the state of alteration of smalt in historical and model samples in order to propose digital reconstructions of the original aspects of the paintings and second, we want to investigate the chemical interactions between the pigment and its environment to have a better understanding on the weathering causes. MicroXANES at the Co K-edge at ID21 has successfully been used to differentiate an altered smalt from a well-preserved one, but the penetration of X-rays at this energy prevents probing the state of weathering at the grain scale. We propose to combine submicronic XRF and high resolution microXANES mapping of smalt grains and their environment at the Co and K K-edges to relate its chemical state to the color of the grains and to follow the chemical transformations of K leached out of the grains本实验聚焦于解析15至18世纪油画中所用的蓝玻璃颜料（Smalt）的劣变机制。其一，我们将对历史样品与模拟样品中的该颜料劣变状态进行定量表征，以期实现油画原作样貌的数字化复原；其二，我们将探究该颜料与其所处环境间的化学相互作用，以更深入地解析其风化成因。此前已成功利用ID21光束线处的钴K边（Co K-edge）显微X射线吸收近边结构光谱（MicroXANES）区分劣变与保存完好的该颜料，但该能量下X射线的穿透性使得无法在晶粒尺度上探究其风化状态。本研究拟结合亚微米级X射线荧光光谱（submicronic XRF）与针对Co、K K边的高分辨该颜料晶粒及其环境的显微X射线吸收近边结构光谱成像，将其化学状态与晶粒颜色相关联，并追踪从该颜料晶粒中浸出的钾的化学转化过程。