A patina is simply the layer of oxidization on the surface of the bronze
where it has been exposed to the air. Unlike iron, which will continue to rust, the patina on bronze protects the metal underneath from oxidizing
While a patina will eventually form naturally, bronze artists often accellerate the process and create different effects by applying solutions of
metalic salts to the surface of the bronze that oxidize it more quickly (especially when heated), as well as adding new colors to the surface through
chemical reactions between the bronze and the patinal solution.
Artists often guard their patina formulas closely, since they can contibribute to the unique look of their work.