Patinas are often used by artists as surface embellishments to change the color and/or texture of an item or surface. Patination composition changes based on the way it reacts to different elements, determining the end color of the patina. For example, copper alloys exposure to chlorides leads to green, while sulfur compounds will turn brown.
Patinas on copper alloys includes chemicals like:
Ammonium sulfide - blue-black patina
Liver of sulfur - brown-black patina
Cupric nitrate - blue-green patina
Ferric nitrate - yellow-brown patina
Patination is often accelerated by applying chemicals along with the use of heat. You can achieve anywhere from a matte sandstone yellow to deep blues, greens, whites, reds and blacks. Once complete, some like to enhance the surface by using wax, oils, or other types of lacquers or clear-coats.