The Fading Mystery of Emerald-Green Pigments
▼ Summary
– 19th-century synthetic emerald-green pigments were highly valued by artists like Cézanne and Monet but degraded over time, causing cracks and releasing toxic arsenic.
– European researchers used synchrotron radiation to investigate whether light and humidity cause this pigment degradation, as detailed in a Science Advances paper.
– Science aids art conservation through X-ray methods, such as identifying metal carboxylate soaps as the cause of blistering in Georgia O’Keeffe’s paintings.
– Metal soap deterioration affects oil paintings across eras, including Rembrandt’s works, prompting studies like the Met Museum’s project on formation causes.
– Recent analyses, including on Rembrandt’s and Corot’s paintings, use advanced techniques to study damaging metal carboxylate soaps in paint layers.
The introduction of synthetic pigments during the 19th century dramatically reshaped the art world, offering artists like Cézanne, Munch, van Gogh, and Monet access to brilliant emerald-green hues. Unfortunately, these vibrant colors came with a hidden danger: over time, they often deteriorated, leading to cracking, uneven surfaces, and the formation of dark copper oxides, along with the release of toxic arsenic compounds.
For those tasked with preserving these priceless works, this degradation presents a serious challenge. Recent findings from European researchers, published in Science Advances, offer new insights. Using synchrotron radiation and other analytical methods, the team investigated whether light, humidity, or both are responsible for the breakdown, and they detailed the specific chemical processes involved.
Scientific methods, particularly advanced X-ray imaging techniques, have become indispensable in art conservation. A 2019 study highlighted a problem at the Georgia O’Keeffe Museum in Santa Fe, New Mexico, where numerous oil paintings had developed minuscule, acne-like blisters over many years. Chemists identified these as metal carboxylate soaps, formed through a reaction between metal ions from lead and zinc pigments and fatty acids present in the paint’s binding medium. These soaps clump together, creating blisters that migrate through the paint layers.
This type of deterioration is not unique to modern works; conservators have observed it in oil paintings from every era, including pieces by Rembrandt. The Metropolitan Museum of Art in New York is actively researching the causes and mechanisms behind metal soap formation in traditional oil paintings. In a related discovery, researchers involved in the Rijksmuseum’s Operation Night Watch identified rare traces of lead formate in a Rembrandt masterpiece during 2023. Earlier, in March 2022, scientists examined the degradation in Jean-Baptiste-Camille Corot’s Gypsy Woman with Mandolin (circa 1870). By applying three complementary analytical techniques under infrared light, they determined the composition of the damaging metal carboxylate soaps that had formed on the painting’s surface.
(Source: Ars Technica)