Article Dans Une Revue Microchemical Journal Année : 2025

Alteration markers of green copper bimetallic pigments in easel paintings by an inter-comparison of analogues and historical samples

Solenn Reguer

Résumé

This paper investigates the alteration of copper acetate (verdigris) and resinate green pigments widely used in oil paintings during the Middle Ages and Renaissance periods. These are bimetallic Cu(II) complexes. Their alteration consists in a color change of these bimetallic pigments from green into brown resulting in a darkening. By combining micro-analysis of both historical painting samples and analogue mock-ups this study elucidates the interactions between pigments and organic oily matrix and the chemical changes leading to the long-term degradation of copper acetate and resinate. Different analytical techniques were combined to characterize browning and identify degradation markers. The use of multimodal micro- spectroscopic techniques with a high lateral resolution (such as scanning electron microscopy, infrared micro spectroscopy, synchrotron photoluminescence, synchrotron micro-X-ray absorption near edge spectroscopy at the Cu K-edge) proved to be successful for the characterization of paint stratigraphy. The study shows the development of the pigment degradation from the surface to the inner painted layers, its facilitated propagation through defects (as cracks) and the influence of light and oxygen. The reproduced alteration in model samples fits with the ageing of masterpiece paintings. Finally, the browning mechanism is attributed to the formation of new copper complexes resulting from the ageing of organic binder and its interaction with copper bimetallic, without any detected structural modification of pigments in altered and non-altered areas.

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Dates et versions

hal-04942544 , version 1 (12-02-2025)

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Citer

Marion Alter, Margherita Donnici, Solenn Reguer, Mathieu Thoury, Matthieu Réfrégiers, et al.. Alteration markers of green copper bimetallic pigments in easel paintings by an inter-comparison of analogues and historical samples. Microchemical Journal, 2025, 209, pp.112541. ⟨10.1016/j.microc.2024.112541⟩. ⟨hal-04942544⟩
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