Fluorescent Painting

Two pictures of the same oil painting obtained in Paris, France in 2009.  The image on the left was illuminated with iridescence light while the one one right was lit with longwave ultraviolet (395 nm) light.  White arrows show three sections of the painting that fluorescent bright orange.

It would be good to know what material in the paint exhibits this illumination property.

Learn more about fluorite and fluorescence at the Delaware Mineralogical Society web site.