New model of outdoor bronze corrosion and its implications for conservation

Luc Robbiola (1) , Christian Fiaud (2) , Stéphane Pennec

1 TRACES - Travaux et recherches archéologiques sur les cultures, les espaces et les sociétés
2 CNRS UA 216 - Laboratoire de Corrosion

A new model that takes into account both the tin and the copper in the alloy is proposed to improve the understanding of deterioration processes of outdoor bronze sculptures. The corrosion mechanism relates to the selective dissolution of copper. Two main processes occur: the process of tin oxidation with the formation of insoluble tin compounds which remain in the corrosion film, and the process of copper oxidation with the migration of copper ions to the surface. Considering this mechanism, the mechanical action coupled to acidity of the precipitations, two different evolutions at the surfaces are suggested. On the surfaces directly exposed to the rain, copper ions are washed out leaving a tin-rich external layer. A cyclic corrosion process is engaged. In the unexposed surfaces, the outermost layer is formed with well-known copper corrosion products. This model can be used to establish the degradation state of outdoor bronze sculptures for a new conservation approach.

Mots clés: Atmospheric corrosion; bronze; conservation; corrosion products; outdoor sculpture; cyclic corrosion

Domaines: Matériaux

Luc Robbiola, Christian Fiaud, Stéphane Pennec. New model of outdoor bronze corrosion and its implications for conservation. ICOM Committee for Conservation tenth triennial meeting, Aug 1993, Washington DC, United States. pp.796-802. ⟨hal-00975704⟩