Pigeons' faeces are highly acidic, corroding historic buildings and stone statues and rusting bridge ironwork. The etchant reacts with the unprotected metal essentially corroding it away fairly quickly. Usually, copper when corroding releases copper ions which have an anti-fouling effect. The polished aluminum wheels are notorious for corroding once the thin lacquer coating is damaged. Nitric acid presented a constant problem, corroding parts and causing skin burns and respiratory irritation. Successful conformal coating will prevent the board from corroding. The fundamental cause are chemical reactions between the worn material and the corroding medium. This showed the details of the oxidation process that was corroding the image. The addition of salt was eliminated in the 1960s, due to it corroding steel structures. "Maheno" has remained at the location since, slowly corroding away. It is also capable of corroding glass.