It is a masterpiece that seems to speak to the later horrors of war in the 20th century and even the anguishes of the 21st. Now Edvard Munch’s The Scream has another claim on modernity, after it emerged that an oversight by the artist means the 1910 version of the work needs to practise some physical distancing. An international consortium of scientists seeking to identify the main cause of deterioration of the paint in the canvas has discovered Munch accidentally used an impure tube of cadmium yellow which can fade and flake even in relatively low humidity, including when breathed upon by crowds of art lovers. The result is that Munch’s initially bright yellow brushstrokes have turned to an off-white colour in the painting’s sunset and in the neck area of the central angst-ridden figure. The thickly applied opaque yellow paint in the lake above the figure is also flaking away from the canvas, which was stolen in 2004 and recovered two years later. “It turned out that rather than use pure cadmium sulphide as he should have done, apparently he also used a dirty version, a not very clean version that contained chlorides,” said Prof Koen Janssens from the University of Antwerp. “I don’t think it was an intentional use – I think he just bought a not very high level of paint. This is 1910 and at that point the chemical industry producing the chemical pigments is there but it doesn’t mean they have the quality control of today.” Scientists from Belgium, Italy, the US and Brazil took part in the investigation. They initially tested whether reducing the painting’s exposure to light may be key to protecting it from further deterioration. “But it turned out that the light is not really very harmful so it doesn’t make sense to reduce light levels below the normal one,” Janssens said. “You have to start working with the relative humidity in the museum, or isolate the public from the painting, or painting from the public, let’s say, in a way that the public can appreciate it but they are not breathing on the surface of the painting.” He added: “When people breathe they produce moisture and they exude chlorides so in general with paintings it is not too good to be close too much to the breath of all the passersby.” The Munch Museum in Oslo is due to move to a new location by the city’s opera house this year and the researchers’ findings are to be incorporated in how the painting is displayed in future. Janssens said: “They can make all kinds of decisions about how they are going to display and protect against whatever environmental conditions. And that is what they said. They will make arrangements to lower the relative humidity. The standard is 50% humidity and they are going to go a bit lower than that.” The discovery of the painting’s fragility was made through luminescence imaging of the canvas to see where the paint was behaving differently, analysis of tiny fragments of paint in Munch’s brushstrokes and in an original tube of cadmium yellow he used. Janssens said: “When you illuminate the painting with UV light, what comes back is some kind of orange light in some locations, and there the paint is in not so good a condition. We tried to figure out why. This orange luminescence seemed to be associated to degradation.” In early 20th-century paint production, cadmium sulphide was produced at times through a reaction between cadmium chloride and sodium sulphide. One theory is that chloride-containing compounds, such as cadmium chloride and cadmium hydroxychloride, may have been left behind in the paint as a result of an incomplete or badly executed reaction. It is hoped that changing the circumstances in which the 1910 version of The Scream is displayed will slow down the degradation, but there is nothing that can be done for water damage clearly visible in its bottom-left corner. Munch painted four versions of The Scream between 1893 and 1910. The 1910 painting was left with a dirty brown water mark when it was stolen along with his Madonna masterpiece by two masked gunmen in a daytime raid on 22 August 2004. The raiders had tackled four unarmed guards, ordered visitors to lie down and ripped the works off the wall before making their escape in a black Audi. The paintings were recovered in 2006. Three men received prison sentences, two of whom were ordered to pay £66m in damages.