Why do EcoCopper building materials change color when used on the exterior of a building?

The natural weathering of copper alloys is a direct consequence of the 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 depends on the location and local weather. Salt, sunlight, industrial processes, and moisture can affect the final color. Clear coatings can provide short-term protection from weathering and will need to be reapplied to prevent weathering. However, some architects and building owners actually require the naturally occurring patina of copper to be accelerated using a controlled chemical process. In general, salmon colored EcoCopper will change hues through a progression of colors until a blue-green or gray-green patina is reached. Depending on the type of alloy used, EcoCopper materials used on the exterior of a building will weather to various patina colors.  more