The Chicago Tribune has a video report about research into the skies in some of Winslow Homer’s watercolors. (Some Homers happen to be in the area (although they’re oils, I believe) including two in the current Coming of Age exhibition at the Meadows Museum of Art).
Art Institute of Chicago researcher Kristi Dahm says that an ultraviolet light scan of a couple of Homer watercolors revealed a pink flourescence that indicated the presence of a faded pigment. Homer was known for his cloud-filled, sun-dappled skies, yet these were blank. It turns out, upon examination, Homer probably used a paint that decayed: The skies were originally given “almost a magenta wash.” The paintings are part of a Winslow Homer exhibition opening at the AIC this weekend.
Unfortunately, the Tribune site won’t let you link directly to a specific clip. So the link above will take you only to the arts & culture page, you’ll have to track down the clip yourself.