(Netherlands) – Scientists use old LED data to highlight why some yellow colours in Vincent van Gogh’s paintings are turning brown due to lighting exposure. Findings sensationalised by mainstream press.
It has been known for some time that the light yellow tones in Vincent van Gogh’s paintings are particularly prone to darkening, but now an international team of scientists have produced a report which suggests that the blue bandwidth in lighting could be to blame.
The experiments were apparently carried out using a Xenon lamp high in UV-A, UV-B, and UV-C wavelengths. Unfortunately the research group, which included scientists from the Van Gogh Museum in Amsterdam amongst others, chose to highlight the danger of LED lighting by publishing a spectral distribution chart from a six year old LED system with a particularly high blue bandwidth. The chart is labelled ‘Emission spectrum of a typical „white“ LED, containing a substantial portion of harmful blue light’.
Even more unfortunately, the report was jumped on by media all over the world printing misleading headlines that LEDs were harmful to van Gogh paintings. Articles quickly appeared in the Daily Mail and The Independent in the UK and the Huffington Post in the USA.
In the report they suggest that all LEDs have a high amount of blue. However, recent developments in museum grade warm white LEDs with high CRI have greatly reduced the amount of blue wavelength present meaning that the bandwidth is now much closer to the black body curve locus.
The paint changes have been blamed on a chemical reduction of chromium, the principle element found in the chrome yellow paint favoured by van Gogh to depict sunshine. However scientists‘ were left baffled as to the cause of the changes and as to why the darkening was more apparent on some canvases rather than others.
Using synchrotron X-rays to better understand the problem, Deutsches Elektronen-Synchrotron (DESY) in Germany and the European Synchrotron Radiation Facility (ESRF) in France examined an extensive series of van Gogh paintings belonging to three museums in the Netherlands (including the Van Gogh Museum) and France. Speck-sized paint fragments taken from the masterworks were examined at the two synchrotron facilities and two heritage labs in Italy and Holland.
It was concluded that the artist did not always use the same type of chrome yellow paint in his work. Van Gogh liked to use a standard lead chromate paint named ‘middle yellow’ but also, due to his poverty, utilised a cheaper ‘lemon yellow’ and ‘primrose yellow’ from time to time. It was these non regular types of paint that were found to be reactive to light in the lab.
The paints affected, which have been found in Van Gogh’s famous ‘Vase with Sunflowers’ and the ‘Portrait of Gauguin’, tended to have a higher sulfate content, with the paint becoming unstable the higher the sulphate levels rose. When exposed to green-blue light those paints containing unstable levels of sulfate turned a brownish/yellow, while ‘middle yellow’ remained unaffected.
Claus Habfast of the European Synchrotron Radiation Facility in France, told the Independent newspaper in London: “LED lights appear to have many advantages but museums should carefully consider that paintings from the Van Gogh era could be affected by them.”
Ella Hendriks, Head of Conservation at the Van Gogh Museum in Amsterdam also commented: “Studies like these are very important to make museum curators aware that, even under ambient light conditions, the degradation of some sensitive materials proceeds continuously. Musea should carefully consider the potential impact of, for example, the new, LED-based, lighting systems that are now being installed in collections.”
However, Rogier van der Heide of Philips Lighting, who acts as a lighting consultant at the Van Gogh Museum and Rijksmuseum in Amsterdam, states: “The use of LED in museums is safe. It is regrettable that the research was published in such a way. The research was correct but the interpretation was wrong.”
Martin Krautter of ERCO, who also manufacture LED lighting for museums, commented: “Paintings using very unstable pigments have to be treated with extreme caution. But to believe that there is a ‘less dangerous’ light source available for these paintings than modern warm white LED is quite ridiculous. If you want to stop degrading, put the paintings away into the dark!”
There is no evidence that LED light damages artwork across the board. Museums that hold works by Van Gogh and Paul Cezanne, who are known to have used the paint in question, are being asked to consider their use of lighting systems with high blue bandwidths when lighting works by Cezanne or Van Gogh and to check masterpieces with infra-red light for the presence of the paint.