Fig. 4: MA-XRF maps and OCT results.

Top row: VIS image of Women with Upturned Nose, courtesy of A. Verburg, KMSKA. The red square indicates the MA-XRF scan area with the resulting barium (Ba-L), cobalt (Co-K), and tin (Sn-L) elemental maps shown on the right. The barium, cobalt, and tin paint strokes appear to be added on a dry paint layer and might be part of the post-factum revision. The yellow square indicates the area of a high-resolution MA-XRF scan results of which are shown in the middle row. Middle row: detail of the UIVFP image, courtesy of A. Verburg, KMSKA. The white arrow indicates a small paint stroke, fluorescing in pink. To the right: detail of the eye in visible light, followed by a composite MA-XRF image of the eye showing Ba-L (red), Co-K (blue), and Sn-L (green) signals. The corresponding paint strokes appear to be added on a dry paint layer. a OCT virtual cross-section showing a region of varnish and red glaze over red paint around the lips. The glaze is confined to the far left of the cross-section. The vertical scalebar corresponds to a depth of 250 µm in air. b Color image derived from the microscopic reflectance spectral image assuming CIE standard 2° observer and D65 illuminant, with cross sections shown in (a, c) marked. c The thickness of the two transparent layers is 11.2 µm and 18.7 µm, assuming a refractive index of 1.5. Multiple layers can only be seen over regions of red glaze.