Why some greens turn brown in historical paintings
(PHYSorg.com Chemistry)

Enticed by the brilliant green hues of copper acetate and copper resinate, some painters in the Renaissance period incorporated these pigments into their masterpieces. However, by the 18th century, most artists had abandoned the colors because of their tendency to darken with time. Now, researchers reporting in ACS` journal Inorganic Chemistry have uncovered the chemistry behind the copper pigments` color change.