Why do metal sculptures corrode when exposed to water and pollutants?

Metal sculptures corrode because they naturally tend to revert to more thermodynamically stable mineral states, such as oxides, hydroxides, or sulfides, which are the forms in which metals typically occur as ores before refinement.12

When a sculpture is exposed to water and pollutants, a thin surface film forms that acts as an electrolytic medium. This environment facilitates a series of electrochemical reactions where different regions of the metal function as anodes and cathodes. At the anode, metal atoms undergo oxidation, losing electrons and entering the environment as cations. These electrons are then gained by oxygen or other oxidizing species, leading to the formation of corrosion products like rust or patina.2

The presence of water is essential to initiate and complete this process, while pollutants, acids, and salts further accelerate the deterioration. While some metals form a compact, protective layer that limits further attack, others—such as iron—form porous products that promote continued corrosion.12