The Patina Process
Patina
The chased bronze is now treated with chemicals and heat to give it the chosen color according to the artists specifications. A true patina is not a surface paint but rather is reacting with the bronze and chemically aging it. Some bronzes may also have paint applied to the surface. The patina is sealed under a wax coating and becomes part of the sculpture.The bronze must be very clean in order to achieve a quality patina. This is most often done by sandblasting although we can use other methods depending on the actual patina that is desired. A final inspection on the work is made by the Patinuer. For a standard French Brown patina we will apply the liver of sulfur to the sand blasted bronze. The bronze will start to change colors almost immediately. Eventually, the bronze will change to a dark brown almost black color. We'll scrub the liver off of the bronze so that the deep parts of the texture and recesses of the form remain dark.
The high points will be shiny and bright. When we get the desired effect, we'll then prepare to apply ferric nitrate. We'll have to heat the bronze with a propane torch. Then we can add the ferric nitrate to the bronze with a brush or a spray bottle. When we get to the desired level of color we'll then seal the patina with a paste wax. For this specific patina we prefer Johnson's paste wax. When the sculpture is cool to the touch we'll then buff out the wax sealer with a clean soft cloth in order to achieve the appropriate shine.
Ferric Nitrate is a solution of iron dissolved in diluted nitric acid. It creates reds, browns and golden colors. Copper or cupric nitrate gives the bronze the green family of colors. We also use several kinds of oxides to produce other colored results. Some patinas are achieved by layering chemicals on top of other chemicals.