Probing the chemistry of CdS paints in The Scream by in situ noninvasive spectroscopies and synchrotron radiation x-ray techniques

The degradation of cadmium sulfide (CdS)-based oil paints is a phenomenon potentially threatening the iconic painting The Scream (ca. 1910) by Edvard Munch (Munch Museum, Oslo) that is still poorly understood. Here, we provide evidence for the presence of cadmium sulfate and sulfites as alteration products of the original CdS-based paint and explore the external circumstances and internal factors causing this transformation. Macroscale in situ noninvasive spectroscopy studies of the painting in combination with synchrotron-radiation x-ray microspectroscopy investigations of a microsample and artificially aged mock-ups show that moisture and mobile chlorine compounds are key factors for promoting the oxidation of CdS, while light (photodegradation) plays a less important role. Furthermore, under exposure to humidity, parallel/secondary reactions involving dissolution, migration through the paint, and recrystallization of water-soluble phases of the paint are associated with the formation of cadmium sulfates

XRDUA : crystalline phase distribution maps by two-dimensional scanning and tomographic (micro) X-ray powder diffraction

Imaging of crystalline phase distributions in heterogeneous materials, eitherplane projected or in virtual cross sections of the object under investigation, canbe achieved by scanning X-ray powder diffraction employing X-ray micro beamsand X-ray-sensitive area detectors. Software exists to convert the two-dimensional powder diffraction patterns that are recorded by these detectorsto one-dimensional diffractograms, which may be analysed by the broad varietyof powder diffraction software developed by the crystallography community.However, employing these tools for the construction of crystalline phasedistribution maps proves to be very difficult, especially when employing micro-focused X-ray beams, as most diffraction software tools have mainly beendeveloped having structure solution in mind and are not suitable for phaseimaging purposes.XRDUAhas been developed to facilitate the execution of thecomplete sequence of data reduction and interpretation steps required toconvert large sequences of powder diffraction patterns into a limited set ofcrystalline phase maps in an integrated fashion

XRDUA : crystalline phase distribution maps by two-dimensional scanning and tomographic (micro) X-ray powder diffraction

Imaging of crystalline phase distributions in heterogeneous materials, eitherplane projected or in virtual cross sections of the object under investigation, canbe achieved by scanning X-ray powder diffraction employing X-ray micro beamsand X-ray-sensitive area detectors. Software exists to convert the two-dimensional powder diffraction patterns that are recorded by these detectorsto one-dimensional diffractograms, which may be analysed by the broad varietyof powder diffraction software developed by the crystallography community.However, employing these tools for the construction of crystalline phasedistribution maps proves to be very difficult, especially when employing micro-focused X-ray beams, as most diffraction software tools have mainly beendeveloped having structure solution in mind and are not suitable for phaseimaging purposes.XRDUAhas been developed to facilitate the execution of thecomplete sequence of data reduction and interpretation steps required toconvert large sequences of powder diffraction patterns into a limited set ofcrystalline phase maps in an integrated fashion

Macroscopic X-ray powder diffraction scanning : possibilities for quantitative and depth-selective parchment analysis

At or below the surface of painted works of art, valuable information is present that provides insights into an object’s past, such as the artist’s technique and the creative process that was followed or its conservation history but also on its current state of preservation. Various noninvasive techniques have been developed over the past 2 decades that can probe this information either locally (via point analysis) or on a macroscopic scale (e.g., full-field imaging and raster scanning). Recently macroscopic X-ray powder diffraction (MA-XRPD) mapping using laboratory X-ray sources was developed. This method can visualize highly specific chemical distributions at the macroscale (dm²). In this work we demonstrate the synergy between the quantitative aspects of powder diffraction and the noninvasive scanning capability of MA-XRPD highlighting the potential of the method to reveal new types of information. Quantitative data derived from a 15th/16th century illuminated sheet of parchment revealed three lead white pigments with different hydrocerussite-cerussite compositions in specific pictorial elements, while quantification analysis of impurities in the blue azurite pigment revealed two distinct azurite types: one rich in barite and one in quartz. Furthermore, on the same artifact, the depth-selective possibilities of the method that stem from an exploitation of the shift of the measured diffraction peaks with respect to reference data are highlighted. The influence of different experimental parameters on the depth-selective analysis results is briefly discussed. Promising stratigraphic information could be obtained, even though the analysis is hampered by not completely understood variations in the unit cell dimensions of the crystalline pigment phases