Fig. 6

a Polarized light and b UV light microphotographs of cross section S7 from Landscape with Snow, i.e. ground preparation and paint, revealing a bright pink layer with a yellow UV-induced autofluorescence, whose superficial portion likely faded upon exposure to light. c HPLC chromatogram of sample S5, i.e. a scraping of pink paint underneath some purple strokes in the field, compared to that of a reference eosin sample. d Visible spectrum of the main peak detected in the chromatogram of sample S5, compared to that of reference eosin