Both natural and man-made bronze patinas are added to sculpture art of any size to create a unique effect and overall appearance. There are a variety of types as well as colors to choose from depending on the desired outcome. When applied by a professional artist experienced in this technique bronze patinas can customize any such art piece.
Originating from the Latin word for “shallow dish”, this finish refers to the exterior shade on metal. The copper within the bronze responds chemically or through oxidation to ultimately alter the original color. This can be achieved naturally as well as through a specialized process. There is evidence of this technique being practiced as early as the 1800’s. When untreated this type of metal is gold in color, despite the changes that may be viewed over time. The original shade changes when exposed to various environmental factors such as weather and skin contact. In this case, bronze patinas are generally in a green range and are commonly referred to as verdigris. It is made up of basic carbonates, sulphides, and chlorides. A prime case of a natural alteration is on the Statue of Liberty. From years of exposure to temperature change and the surrounding water the surface has taken on a green tone.
Many artists choose to create a forced change to the metal’s surface. This may be done to achieve a specific color or texture as well as to give it a distressed appearance. To achieve the best possible effect through this process the piece should contain a minimum of 90% copper. Each chemical option will have a different response when in contact with the metal. Chlorides such as cupric nitrate tend to leave a green tone while liver of sulfur results in some shade of brown. Ferric nitrate will provide a red or mustard-like color and ammonium sulfide leaves a darker black or blue surface. Additional shades can be created with the use of pigments that are mixed with the chemicals prior to application. Some artists will apply bronze patinas through hot or cold methods. Cold application utilizes more potent chemicals and can take longer to affect the appearance. It is commonly used to make minor repairs or color adjustments. On the other hand, the hot technique creates a quicker change to the surface and can be highly manipulated by the artist for more customized work.
More specifically hot patinas are put on through an intricate process performed by an experienced artist. The metal is heated to at least 200 degrees at which time the chemicals are brushed or sprayed on to cover the piece entirely. Depending on the desired texture or color, the artist will allow the chemical to react with the metal until it is achieved. The chemical reaction is then stopped by placing the metal under cold water. Prior to complete cooling, the piece is covered in a couple layers of wax to protect the newly altered surface.
Bronze patinas can be found on various pieces from decorative dishes to full scale sculptures. Whether altered naturally over time or influenced by chemicals, the effect is unique to each and every work of art. It can ultimately provide a conversation piece to a home or even a well known centerpiece to an outside landscape.