What causes the corrosion of copper?
Constant high humidity, pollutants such as sulphide gases, acids and careless handling causing physical damage can all cause deterioration of copper-based objects. In addition, heating and acidic cleaning solutions can etch the zinc out of brasses leaving a copper-red discolouration on the surface. Copper and copper alloys which have been buried or recovered from a wet site can suffer from the effects of chloride salts, resulting in the development of bronze disease. Objects may also have special surface coatings, such as lacquers, which can be damaged easily by scratching or improper cleaning. Cleaning copper and copper alloys Items which are in good condition need only be wiped with a dry cloth. Alcohol, preferably ethanol, may be used to remove greasy stains, but only after spot-testing to ensure there are no surface coatings that will be affected by this solvent. If a badly tarnished copper alloy must be cleaned, immerse it in a solution of 10g of thiourea and 50g of citric acid in
