Aged copper displays a protective layer of rich blue-green patina, also known as verdigris. Rather than waiting the five to seven years it takes for new copper to naturally develop a patina when exposed to the elements, you can get that look now. A lovely patina is possible through the use of a patina kit or homemade concoctions.
The Patina Look
The patina that grows on aged copper is the result of exposure to the elements, especially areas close to saltwater. Salt in the air, combined with water and oxygen, reacts with the copper metal through oxidation. The reaction changes the metal surface by forcing some of the copper molecules to bond with oxygen, salt or other molecules. Compounds that make up verdigris include copper sulfate, copper carbonate and chloride salts. Copper sulfate is a bright blue-green color and gives most verdigris its beautiful color.
Create a Homemade Patina
Start by washing the copper with mild dish soap to remove all oils that may resist the patina. A little baking soda rubbed into the copper along the grain helps scrub away microscopic particles. After rinsing, soak the copper in a 1-to-1 ratio of white vinegar and salt in a small bowl for half an hour. The wet copper is placed on a towel to air dry. Crafters may sprinkle a small amount of salt on the wet copper to encourage the patina to develop. This process may take anywhere from a few hours to a few days to develop.
Use a Patina Kit
A patina kit puts patinas of a variety of colors, including the traditional blue-green, red, brown and black, on new copper within a few hours. Before applying the patina, clean the copper thoroughly with a cleaning pad and an abrasive. Rinse the metal with clean water and dry. Find both acid-free hot application patina kits and acid-containing cold application patina kits in stores. Apply the patina with a brush, sponge or roller. Place it in indirect light for two to three hours while the patina develops.
Working with a commercial patina kit that contains acids may be hazardous. Wear protective rubber gloves, mask and safety glasses during the application process. Work outdoors, under a ventilation hood or in a well-ventilated area, to avoid inhaling acid fumes. Hot application patina kits require the use of a heat gun to warm the metal, which could cause burns to the skin. Treat the patina carefully; it is softer than the copper and can flake off easily. A coating of clear polyurethane spray helps protect the patina on finished projects.