Patination of Lead: An Infra-Red Spectroscopic Study

The corrosion products formed on milled lead sheet exposed outdoors for periods of up to 18 months, and the patina found on lead cladding which had been on the exterior of buildings in rural and urban sites for between 43 and 129 years, have been studied by infra-red spectroscopy. It was found that, during the early stages, basic lead carbonates are the major corrosion products. On further exposure, the carbonates react with sulphur dioxide and sulphur trioxide giving a film composed of a mixture of normal lead sulphite and normal lead sulphate. Subsequently, the major part of the sulphite is displaced giving a protective film of normal lead sulphate. The sequence of reaction products reflects the relative abundance and acidity of carbon dioxide, sulphur dioxide and sulphur trioxide in the atmosphere.