Red Bronze Disease on Brass

Reaction

• When copper is exposed to acidity, a chemical reaction forms cuprous chloride, the primary agent in patination. Exposed to water, hydrochloric acid forms, along with cuprous oxide. As the patina thickens, the cuprous oxide takes on a purple-red color. Bronze disease is more than patination, as it may cause rapid deterioration of brass, bronze or copper objects.

Prevention

• Small objects can be coated with wax before the process of patination begins to prevent air and humidity from reaching the surface of the object and causing the chemical reaction. Once bronze disease begins, it is difficult to stop, because the two chemicals responsible continue to react in tandem.

Cleaning

• Objects may be placed in a five percent solution of sodium sesquicarbonate, or a six percent solution of Benzotriazole in ethanol to remove the patina. The process does not stop patination, but will dissolve it after two to four weeks. Objects experiencing deterioration should be professionally cleaned.

Coloration

• When cuprous oxide thickens on the brass, the color becomes a purplish-red, and is called red bronze disease. Sulphides can turn the object black, and sulphates will change the color to green.