Developing microchemical imaging for the study of pigment degradation in oil paint

Oil paints are complex and heterogeneous systems that undergo various chemical transformations. Such transformations can lead to a degraded visual appearance or lowered mechanical stability of oil paintings. For this reason, the study of oil paint chemistry is of crucial importance for the conservation of many historical works of art. This thesis explores various advanced microchemical imaging methodologies in terms of their applicability for studying pigment degradation in oil paint. Chapter 2 first gives a comprehensive overview of the state-of-the-art of microchemical imaging in the study of oil paint degradation. Chapters 3, 4, and 5 then present three studies in which deep-UV multispectral and hyperspectral photoluminescence microimaging is demonstrated to reveal information on intrinsic pigment properties and pigment degradation products in historical microsamples. Chapter 6 discusses the application of X-ray microscopy for the study of the pigment zinc white (ZnO). Although originally intended to reveal chemically relevant intrinsic crystal defects (see Appendix B), it is described here how the data in fact uniquely allows to quantify X-ray natural linear dichroism on powders. Chapter 7 then continues to describe how the X-ray microscopy technique introduced in chapter 6 can be developed into an X-ray excited optical luminescence (XEOL) microscope. This newly developed technique is shown to be uniquely capable of simultaneously recording X-ray absorption and optical luminescence spectra at a spatial resolution exceeding the diffraction limit of visible light. Finally, by looking at recent technological developments in other fields of research, chapter 8 discusses the future prospects of microchemical imaging applied to studies of oil paint degradation.