Recent studies proved that antique cultural heritage bronze artefacts were intentionally patinated using a chemical treatment. Patina appear on artefacts from Egyptian civilisation, Greek civilisation and Roman Empire. They are named, depending on the artefacts origin, black bronze, or corinthium aes and are applied to copper alloys containing gold and/or silver. It was compared with a medieval Japanese patina known as "shakudo". During the last four years, an important study of antique artefacts coming from the collections of French museums was carried out. An experimental protocol based on non-destructive analysis was developed to analyse these very precious object and to identify and characterize this type of patina as a function of the provenance and age of the artefacts. However some questions about this particular surface layer could not be solved using this experimental protocol due to the limitation of non-invasive analytical techniques: In particular the question of the oxide layer formation, the colouring mechanism of the black cuprite (copper oxide which is red under natural form) and the important adherence properties. An experimentation program was developed to reproduce black patina, based on the use of Japanese recipes. We tried to differentiate the effect of the alloying element (Au, Ag, As, Sn) and the effects of the chemical treatment. These patinas were studied by means of several analytical methods. In particular, TEM was used to characterize the fine structure of the oxide layer. The aim of this paper is to present the results obtained and the contribution of TEM. The objective is to study the bronze/patina interface on an atomic scale. The preparation of the samples was particularly neat. Strong roughness (μm) and the heterogeneity of the patina required the development of strategies adapted for obtaining thin blades, strategies which will be exposed. The difficulty in obtaining transverse cuts of good quality by a traditional method led us to prepare the samples by FIB (Focussed Ion Beam). Within this framework, various techniques of cutting of membrane were tested. We will underline the advantages and the difficulties related to this method of preparation. The first results of the observations MET will be exposed.
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