COLOR WHEEL
Copper is widely recognized by its aged green hue, or patina. But what causes the patina? And why does the metal turn colors in some applications but not in others?

A patina is a naturally occurring coating that forms when the metal is exposed to certain elements in the air, according to copper.org—the Web site for the Copper Development Association Inc., an organization composed of copper manufacturers and distributors across North America. The amount of time it takes for this oxidization to occur can depend on several factors. For example, copper likely will develop a blue-green patina faster in humid areas or locations that receive frequent rainfall. The site notes that the natural coating is “highly resistant to all forms of atmospheric corrosion, once it has had an opportunity to form completely. It thus significantly increases the durability, and, hence, the service life of copper roofing and flashing.”

Over the years, chemical finishes have been developed that can quickly re-create the look of a weathered patina. The Web site states that homeowners desiring a copper application that retains the metal’s original salmon-colored hue may opt for a protective finish that establishes a barrier and prevents oxidization. The site notes that these types of finishes will degrade over time and need to be reapplied to maintain the desired result.