Visualizing a black cat drawing hidden inside the painting by confocal micro-XRF analysis

We investigated the nondestructive 3D elemental analysis of a paint sample using a confocal 3D-XRF spectrometer. The confocal 3D-XRF spectrometer combined with two polycapillary X-ray lenses was constructed in the laboratory. To confirm the analytical performance of the confocal 3D-XRF spectrometer, we analyzed several pigment mixtures of Emerald green (EG) and Prussian blue (PB). XRF intensities of Cu and Fe in the pigment mixtures showed good correlation with the content percentage of PB. In addition, we analyzed the replica paint in Daubigny's garden by Vincent Van Gogh to visualize a hidden painting beneath the surface. 3D-elemental map of Fe by confocal 3D-XRF showed characteristic distributions indicating the PB. The obtained 3D-XRF intensity imaging reflected the distribution of specific elements in the paint layers resulting in the successful visualization of the hidden cat.