New strategies for the conservation of paintings on metal

International audienceThe conservation and restoration of painted metal objects presents a challenge due to their composite nature. Both the metal support and the paint layers can undergo independent and linked alterations, making it necessary to fully understand the processes of degradation before attempting to implement a treatment. This paper presents the first part of the CoPaiM project, detailing the selection of a corpus from the collections of the Musée des Arts et Métiers in Paris, France. A condition report on 23 painted metal objects was prepared including a description of the materials, their visible alterations and a first diagnosis of whether the degradation originated from deterioration of the paint or corrosion of the metal support. Samples of paint and corrosion products were collected from six objects in order to characterize the system by micro-analysis. A multi-technique analytical methodology was used to study the morphology, the elemental composition and distribution and the variety of phases present in the samples, thus allowing a complete characterization of the metal, the corrosion products and the components present in the paint layers. Aesthetic alteration of the paint was observed in cases where the degradation of the metal support had led to subsequent migration of the corrosion products into the paint layers, leaving a brown-orange stain. The paint layers were determined to have oxidized over time, which could affect their stability in the composite system. The next steps of this project are to summarize the analytical data into hypotheses for the degradation mechanisms of the paint-metal system