Morphology and mechanisms of formation of natural patinas on archaeological Cu–Sn alloys

Natural patinas on archaeological bronzes (Cu–Sn alloys) have been classified and characterized in order to get a deeper insight into their formation mechanisms. From examinations of cross-sections on archaeological artefacts, two classes of corrosion structures were defined (Type I and Type II), us...

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Bibliographic Details
Published in:Corrosion science 1998-12, Vol.40 (12), p.2083-2111
Main Authors: Robbiola, L, Blengino, J.-M, Fiaud, C
Format: Article
Language:English
Subjects:
Applied sciences
Atmospheric corrosion
Bronzes
conservation of metals
Copper base alloys
copper selective dissolution
copper-tin alloys
Corrosion
Corrosion mechanisms
corrosion structures
Environment
Exact sciences and technology
Historical artifacts
Historical metallurgy
Metals. Metallurgy
modelling
Morphology
Patina
Pitting (corrosion)
Sea water
Soil (material)
Uniform attack (corrosion)
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Summary:Natural patinas on archaeological bronzes (Cu–Sn alloys) have been classified and characterized in order to get a deeper insight into their formation mechanisms. From examinations of cross-sections on archaeological artefacts, two classes of corrosion structures were defined (Type I and Type II), using both optical and electron microscopies, EDSX, XRD, IRS and a statistical treatment of data (Principal Components Analysis). A Type I structure (even surface) is defined as a two-layer passivating deposit due to an internal oxidation with a decuprification process (i.e. selective dissolution of copper). A Type II structure (coarse surface) corresponds to more severe attacks, such as pitting but also general uneven corrosion; it is modelled by a three-layer structure, characterized by the presence of cuprous oxide and by an increase in the chloride content at the internal layer/alloy interface related with selective dissolution of copper. A phenomenological model to explain the formation of bronze patinas is developed on the basis of a decuprification phenomenon.
ISSN:0010-938X
1879-0496
DOI:10.1016/S0010-938X(98)00096-1