An international team of researchers have found what triggers degradation in one of the most popular pigments used by renowned 19th and 20th century painters. Using a multi-method approach, including advanced synchrotron radiation techniques, they’ve unveiled how light and humidity affect the masterpieces over time, and have proposed a strategy for its mitigation and monitoring. The results are out now in Science Advances.
During the 19th century, the Second Industrial Revolution sparked major advances in chemistry, giving rise to synthetic pigments that transformed art. Among them was emerald green, a vivid copper arsenite pigment admired for its brilliance and intensity.
Emerald green was used by well-known late 19th and early 20th century painters, such as Paul Cézanne, Claude Monet, Vincent van Gogh, Edvard Munch, and Robert Delaunay. Some of these painters, including Van Gogh, quickly realised that the paint would change over time, losing its original brilliant colour, cracking and triggering surface deformations. It was discovered later that it was also highly toxic.
Light and humidity
Researchers believe emerald green degrades because its chemical composition is highly unstable under light, humidity, and certain atmospheric gases. These conditions can cause the pigment to react and release arsenic compounds, alter its colour, or form dark copper oxides.
Now a research team led by the Institute of Chemical Sciences and Technologies “Giulio Natta” (SCITEC) of CNR and the Department of Chemistry, Biology and Biotechnology of the University of Perugia, in collaboration with the ESRF, the European Synchrotron, and the University of Antwerp, has investigated what triggers the degradation of emerald green. The study1 aims to improve strategies for preserving the masterpieces containing this pigment and to develop new methods to monitor their conservation state. “It was already known that emerald green decays over time, but we wanted to understand exactly the role of light and humidity in this degradation”, explains Letizia Monico, senior researcher at the SCITEC-CNR, corresponding and first author of the publication, together with Sara Carboni Marri, a former PhD student from the same research group.
Read more on the ESRF website
Image: Photograph of The Intrigue (1890, Royal Museum of Fine Arts Antwerp, KMSKA) by James Ensor
Credit: Royal Museum of Fine Arts Antwerp, KMSKA