Copper takes form in many ways and applications in our built environments. Plumbing lines, plumbing fixtures, electrical conducting applications, as an architectural metal for the exterior skin as siding or roofing and many others, the precious metal also is at the whim of exterior and interior environmental effects. Moisture in the air and in direct contact oxidizes the mineral creating a patina, which is the greenish substance that results from the oxidation process. Depending on the humidity of a given geographic location, the patina may turn a very dark brown or even close to black. In many of these applications, it is critical to seal or protect the copper to keep the environmental effects from eroding the finish and over time the integrity of this softer metal. Architectural copper applications, depending on the product, like a bathroom sink for example, copper can be sealed or left unprotected. When unprotected, the copper sink has what is known as a living finish, eventually resulting in the greenish patina, as would other metals like brass and iron create their own patinas and living finish.
In many applications, copper is used both for practical and functional reasons and also for aesthetic and decorative purposes. Over the years various chemical combinations have been developed and applied to architectural copper for the purpose of advancing the “age” of the copper living finish to the desired color and is known as applying a patina to the metal. One is called Liver of Sulfur, and also goes by the names Potash Patina and Sulfurated Potash and contains several chemical compounds that are the active ingredients for the premature aging affect.
The above photo, on this residential application, shows a newly installed exterior light fixture that was constructed of copper and will age, or oxidize, naturally over time from the Colorado air, rain and snow. On the adjacent wall, the siding is composed of copper tiles creating a look that is similar to a shingle siding. The copper was applied with the Potash Patina thereby giving it the dark brownish-grey patina that you see. This is still considered a living finish because it will not be sealed to maintain the current color, but will continue to oxidize.