To also learn how the drawing was executed. Original sketches may underlay the final paint. Van Gogh was a rapid painter and didnt paint in stages that much. Bu

To also learn how the drawing was executed. Original sketches may underlay the final paint. Van Gogh was a rapid painter and didnt paint in stages that much. But someone like DaVinci who worked on the same painting for years, if not a decade, reveals various changes from original conception. In addition to Xray there is hyperspectral imaging and fluorescent imaging. Hyperspectral photographs at many different optical colors and extra-optical light. That revealed some techniques of creating the Mona Lisa.