Why Does Bronze Turn Black

Bronze will oxidize when exposed to air, developing a patina coating. A brown, black, red or blue to green coating on bronze is a sign of normal, harmless corrosion. This outer layer protects the inner layers of the bronze object from deteriorating. This coating is sometimes considered attractive or desirable, as well.

What causes bronze to darken?

Heat will darken the color as well as reduce mottling. Liver of Sulfur is the classic darkening patina for bronze, brass, and copper. Depending on the surface, the strength of the solution, and the application method, it will produce a golden brown to a burgundy black patina.

How do you fix discolored bronze?

Mix together powdered chalk and denatured alcohol to form a thick paste. Scoop up some paste onto a clean cloth and rub it into the surface of the bronze. This polishes the surface of the metal and remove mild corrosion, such as that produced by finger oils. Rub the paste into the bronze using a buffing motion.