In the famous painting “The Intrigue” (1890) by the painter James Ensor, preserved in the Royal Museum of Fine Arts in Antwerp (Belgium), the bright green that dominates the scene shows signs of fragility. An international team of researchers has revealed the chemical mechanisms that cause the degradation of the emerald green pigment, one of the most widespread colors in art between the 19th and 20th centuries, used by masters such as Vincent Van Gogh, Claude Monet and Paul Cézanne. The results were obtained thanks to the use of portable instruments and X-ray techniques which allow the degradation processes to be identified early and their evolution to be followed over time. The study, published in the journal “Science Advances”, paves the way for new preventive conservation strategies for numerous masterpieces.
Emerald green, based on copper arsenite, was introduced in the 19th century and immediately became famous for its brilliance and chromatic intensity. However, its instability was known to artists of the time: Van Gogh already observed that color tended to lose its shine over time.
The research team coordinated by the ‘Giulio Natta’ Institute of Chemical Sciences and Technologies (Cnr-Scitec) and the Department of Chemistry, Biology and Biotechnology of the University of Perugia, in collaboration with the ESRF (European Synchrotron of Grenoble), DESY (Synchrotron of Hamburg) and the University of Antwerp, conducted non-invasive analyzes on the painting by James Ensor, painter and engraver, born in Ostend, Belgium, in 1860, among the exponents of the artistic revolution between the nineteenth and twentieth centuries. The oil on canvas “The Intrigue” is among the most enigmatic paintings of his production. Characters with brightly colored clothes and masks, including green, stand out against the background created in light tones.
The analysis on the masterpiece was carried out by integrating portable non-invasive methodologies and X-ray examinations generated by synchrotron radiation. “It was already known that emerald green degrades over time, but our goal was to understand exactly the role of light and humidity in this process”, explains Letizia Monico, researcher at Cnr-Scitec.
“The investigations have allowed us to identify two distinct mechanisms: humidity favors the formation of arsenolite, a crystalline compound that makes the paint fragile and subject to flaking, while light causes the oxidation of arsenic on the surface, creating a thin whitish layer that dulls the original colour”, adds Aldo Romani, professor at the University of Perugia.
Research demonstrates how technologies and science are allies in the protection of cultural heritage. Initially, non-invasive in situ analyzes were performed on the canvas, on a macro scale, to evaluate the composition and state of conservation of the green areas, identifying the most suitable points for micro-sampling. The diagnostic investigations were carried out using the portable instrumentation of the research groups of the University of Antwerp, with the support of the Molab (Mobile Laboratory), a mobile laboratory coordinated by the Institute of Cultural Heritage Sciences (ISPC) of the CNR and belonging to the European Research Infrastructure for Heritage Science, E-Rihs. “Non-invasive molecular techniques are essential tools: they allow us to obtain in-depth information on materials without sampling, direct micro-sampling in a targeted manner and allow us to intercept any degradation phenomena early”, comments Costanza Miliani, coordinator of Molab and interim director of the Cnr – Ispc.
The next step was to subject microsamples taken in a targeted manner to X-rays produced by synchrotron radiation on a sub-micrometric scale at the cutting-edge laboratories of ESRF and DESY, combining different techniques. “The analyzes carried out are essential for this type of study, since they are the only ones capable of providing specific stratigraphic information on the nature of the different arsenic compounds on a micrometric scale”, explains Marine Cotte, ESRF scientist. Comparing these results with those obtained on specimens artificially prepared with emerald green oil paint and then aged, the team came to the conclusion that it is light that constitutes the main threat to “The Intrigue” by James Ensor and, presumably, to other masterpieces created with emerald green pigment. However, new advanced instruments can help identify the effects on paints early and monitor them over time.
This information is crucial for developing targeted conservation strategies. The research, developed within the Cultural Heritage Innovation for Next-Gen Sustainable Society (Changes, Spoke 5), funded by the European Union – Next Generation Eu, Pnrr aims to optimize the methodologies for monitoring and preventing degradation, guaranteeing the protection of works created with synthetic pigments, the result of the second industrial revolution.