Conservation and alteration of painting pigments: the case of green copper-based organometallic pigments

International audienceGreen copper organometallic pigments have been known since Antiquity. Some of them, such as verdigris and copper resinate, were widely used in easel paintings from the 15th to 17th centuries, for their transparency, brilliance and pure green tones.However these pigments often undergo chromatic modifications, like browning or darkening. This phenomenon is not systematic, and altered and non-altered areas can coexist in a same painting.The understanding of the darkening process is crucial for conservation issues, to improve the readability of degraded paintings and decide how to treat them