The modern pigment composed of cadmium sulphide, discovered because the color used by the Catalan painter when alive and intense has degraded
The mystery of ‘revealedyellow’ by Mirò. In the photo that portrays him in 1978 sitting in his Taller Sert, the famous Catalan surrealist painter Juan Miró he is surrounded by his people paintings. In the background, the bright yellow and intense of Femme dans le rue, painted in 1973. Fifty years later, that cadmium-based yellow appears faded and degraded. The same phenomenon affected another 25 paintings preserved by the Fundació Miró Mallorca. But what really happened? A group of researchers from the Polytechnic of Milan and the Ca’ Foscari University of Venice explained this in a new and detailed study. The degraded yellow of Mirò’s paintings is in fact made of cadmium yellow, a modern pigment, composed of cadmium sulphide and introduced at the end of the 19th century.
The pigment was used extensively by artists such as Vincent Van Gogh, Pablo Picasso and Henri Matisse, who appreciated its brilliance and fullness of color tone. In recent years, however, it has been understood that this pigment is not always stable, leading to a degradation of the painting, as has been highlighted in important works of art including The Scream by Edward Munch. The research conducted so far has made it possible to understand the degradation process, but has not completely clarified what the factors that stimulate this degradation are. It has also been observed that this degradation appears above all in paintings dated between the end of the 19th century and the beginning of the 20th, that is, in a period in which the methods of synthesis of the cadmium yellow pigment had not yet been completely perfected.
Miró’s works, painted in the 1970s, date back to a decidedly later period. Therefore, the Fundació Miró Mallorca collection represents a unique case study for understanding the deterioration of this paint at a later stage in the history of the production of cadmium yellow pigment. To discover the reason for this degradation, the conservators turn to the restorer Mar Gomez Lobon, who brings together an international team that includes the Italian scientists Daniela Comelli and Marta Ghirardello of the Polytechnic of Milan and Francesca Caterina Izzo of the Ca’ Foscari University of Venice. The researchers and their colleagues analyzed nine samples taken from paintings, tubes of paint, artist palettes, using different analytical techniques: electron microscopy, X-ray fluorescence at the Grenoble synchrotron, infrared spectroscopy, microphotoluminescence and chromatographic analyses.
The group of experts explains that the chemical composition of the paints and the crystalline structure of the pigments are the clues that lead the research team to argue that the degraded colors based on cadmium yellow come from tubes of paint produced by the French brand Lucien Lefebvre- Foinet. Miró favored the Parisian manufacturer: over one hundred tubes of paint from the French brand were found in his studios, including five of that now unrecognizable Cadmium Lemon Yellow No.1. It was certainly not a cheap brand: the Parisian house produced high-quality colors used by artists such as Mondrian, Matisse and Giacometti. “The low crystallinity of the pigment exposes it to a high photo-chemical reactivity. This is among the main causes of the vulnerability of the paint and can be traced back to the method with which the pigment was synthesized, a method which however is not known and of which there are no historical sources have not yet been found” explains Daniela Comelli of the Physics Department of the Polytechnic of Milan.
Finally, the environmental conservation conditions strongly contributed to the chemical-physical transformation of the material. Samples with the same chemical composition show different levels of degradation, and the best preserved color comes from a palette that has remained closed in a drawer for 32 years, protected from light and changes in humidity. Francesca Caterina Izzo, of the Ca’ Foscari University of Venice, underlines that “to preserve Miró’s cadmium yellow, like that of other artists, it is necessary to control environmental parameters, including exposure to light and relative humidity” . “In cases of very degraded and therefore fragile pictorial surfaces – continues the researcher – protection with glass capable of filtering ultraviolet radiation can help, while solutions that involve the application of paint protectants and consolidants deserve further study”.
The research, published by the scientific journal Heritage Science, was conducted by the restorer Mar Gomez Lobon together with Marta Ghirardello and Daniela Comelli of the Polytechnic of Milan, Enric Juncosa Darder of the Fundació Pilar i Joan Miró in Mallorca, Carlos Palomino Cabello and Marta Bauza of the Universitat de les Illes Balears, to Marine Cotte of the European Synchrotron Radiation Facility, to Austin Nevin, Aviva Burnstock and Silvia Rita Amato of The Courtauld Institute of Art, and to Francesca Caterina Izzo of the Ca’ Foscari University of Venice. The research on Mirò’s ‘yellow’ will continue in the future with research that will be conducted on other colors of the Lucien Lefebvre-Foinet brand and on paintings containing cadmium yellow paints which, although preserved in a similar way, have not shown the same signs of aging .