Heritage maintenance: Metalwork

Most metals slowly oxidise when exposed to atmospheric conditions, changing to another form such as the mineral ore from which they were produced. Rusting iron and steel produce reddish iron oxide. Some metals such as gold and certain stainless steels are more resistant than others to this process (or more noble) and remain largely unaffected. 

The process of chemical reversion, or corrosion, is accelerated by air pollutants, acid rain, salts and the presence of dissimilar metals. In coastal environments metals corrode rapidly under the influence of airborne salts and high humidity.