Failure of ultramarine blue paint layers in historic as well as modern paintings has been reported in the literature many times and is often referred to as “ultramarine disease” or “ultramarine sickness.” The pigment itself is known to degrade hydrolytically when exposed to acids, but whether this is the primary cause of the failure remains unclear. This paper describes a study in which ultramarine blue paints using linseed oil and a urea-aldehyde resin as binding media were aged under simulated indoor conditions. The paints were analyzed using reflectance spectroscopy, scanning electron microscopy, and Raman and nuclear magnetic resonance spectroscopy. The urea-aldehyde resin binding medium was analyzed using size exclusion chromatography and Fourier-transform infrared spectroscopy. The study provides evidence of photo-catalytic degradation of binding media of ultramarine blue paint layers via free-radical processes, causing changes in reflectance while the pigment itself remains intact. It is believed that this is the primary process behind the degradation of ultramarine blue paint layers in paintings.@en

The paintings by Édouard Manet in The Courtauld Gallery Déjeuner sur l'herbe (1863-68), Marguerite de Conflans en Toilette de Bal (1870-1880), Banks of the Seine at Argenteuil (1874), and A Bar at the Folies-Bergère (1882) were investigated for the first time using a range of non-invasive in situ analyses. The aims of the study were to investigate the painting techniques and materials used for this group of works and to critically evaluate the technical evidence derived from the integrated use of imaging techniques and portable spectroscopic methods in this context. The paintings were investigated by means of macro X-ray fluorescence (MA-XRF), reflection spectral imaging, portable UV-Vis-NIR spectroscopy, portable Raman spectroscopy, and reflection FTIR. MA-XRF and reflection spectral imaging allowed visualising elements in the compositions that were not visible using traditional methods of technical study. For example, MA-XRF analysis of Déjeuner sur l'herbe revealed elements of the development of the composition that provided new evidence to consider its relationship to other versions of the composition. The study also highlighted questions about the interpretation of elemental distribution maps and spectral images that did not correspond to the reworking visible in X-radiographs. For example, in A Bar at the Folies-Bergère Manet made numerous changes during painting, which were not clearly visualised with any of the techniques used. The research has wider implications for the study of Impressionist paintings, as the results will support technical studies of works by other artists of the period who used similar materials and painting methods.@en

Paintings by Édouard Manet from the Courtauld Gallery including Le Déjeuner sur l’herbe (1863-68), Marguerite de Conflans en Toilette de Bal (1870-1880), Banks of the Seine at Argenteuil (1874), and A Bar at the Folies–Bergère (1882) have been investigated for the first time using a combination of non-invasive in situ analytical methods. These included multispectral and hyperspectral VIS-NIR imaging, macro X-ray fluorescence (MA-XRF), portable reflectance and fluorescence UV-Vis-NIR spectroscopy, portable Raman spectroscopy, and portable reflection FTIR, provided by collaboration with the University of Delft, University of Antwerp and the European mobile platform MOLAB. The study also included analysis of paint samples using light microscopy and SEM-EDX. The aims of the study were to investigate the painting techniques and materials used for this group of works, and to critically evaluate the evidence derived from the application of non-invasive site-specific analyses and imaging techniques, highlighting their advantages and limitations in this context. The analytical methods used provided evidence for the identification of a range of inorganic pigments and classes of organic materials used for the works, and it was possible to image underlying elements in the compositions using elemental mapping and NIR imaging that were not visible using traditional methods of technical study including X-radiography and IRR in a more limited range. The study highlighted questions in relation to the interpretation of elemental distribution maps and spectral images that did not correspond to the reworking visible in X-radiographs. This question is exemplified in the study of the iconic A Bar at the Folies–Bergère that Manet reworked during painting, making numerous changes directly on the canvas that were not clearly visualised with any of the techniques used. Contrastingly elements of the development of the composition of the Courtauld’s Le Déjeuner sur l’herbe were revealed using MA-XRF that provided new evidence to consider its relationship to other versions of the composition. This paper will describe the preliminary results and discuss some of the challenges in interpretation of the data. Acknowledgment The EU project IPERIONCH Integrated Platform for the European Research Infrastructure on Cultural Heritage (GA n. 654028, www.iperionch.eu) is acknowledged for transnational access to portable non invasive instruments (multi/hyperspectral VIS-NIR imaging, MA-XRF, reflectance and fluorescence UV-Vis-NIR spectroscopy, Raman spectroscopy, and reflection FTIR) belonging to the MOLAB platform. @en