Corrosion Products of Copper
Copper oxides can further react with other chemicals to produce a substance known as verdigris. This is often the result of copper weathering in the presence of sea water.
Verdigris is the common name for a green pigment obtained through the application of acetic acid to copper plates or the natural patina formed when copper, brass or bronze is weathered and exposed to air or seawater over a period of time. It is usually a basic copper carbonate, but near the sea will be a basic copper chloride. If acetic acid is present at the time of weathering, it may consist of copper(II) acetate. It is this set of reactions that gives the Statue of Liberty its green colour.
Physical Properties of Copper Oxides
When copper oxidises, it forms a thin impermeable layer that forms a protective surface. This thin film acts to prevent further corrosion. In low oxygen environments, such as stagnant water, this protective film cannot form but without it, copper is susceptible to other forms of corrosion such as galvanic effects and chemical attack from such things as sulphates and carbonates.