Why does copper change color?
The natural weathering of copper is a direct consequence of the corrosive attack of airborne sulfur compounds. This leads to a gradual change in the surface color until equilibrium is reached and the change is stabilized. The final color is different and depends on the location and local weather. Salt, moisture, sunlight and orientation can effect the final color. In general, copper changes in hue from a natural salmon through a progression of russet browns, grays and finally to a blue-green or gray-green patina.
