Exposed to the elements, many metals oxidize. When they do, they change colors. Copper and bronze will sometimes develop an attractive verdigris of green. As they weather, metals will also darken, turning their brassy colors to antique hues of brown. The term most frequently used for the weatherworn coloration that metals develop is patina. With...
http://supply55.com/blog/2014/03/toning-metal-leaf-with-liver-of-sulfur-2/
