Paintings by Dutch artist Vincent Van Gogh and French painter Henri Matisse are losing their bright yellow hues due to chemical reactions in the paint and thus are at risk of fading.
Researchers found that the cadmium yellow pigment which was used widely by Impressionist, post-Impressionist, and early modernist painters is already starting to discolour and is likely to get worse.
They noted that in paintings such as 'The Joy of Life' by Matisse and 'Flowers in Blue Vase' by Van Gogh, discolouration of cadmium yellow has changed the general appearance and colour balance of the paintings so that they now look significantly different.
Large areas in 'The Joy of Life' which were originally bright yellow areas have now acquired an ochre-beige tint, 'The Telegraph' reported. Researchers from the European Synchrotron Radiation Facility (ESRF,) in France used X-rays and infrared microscopy to analyse the make-up of tiny samples of damaged paint.
They found that the original chemical compound used to make cadmium yellow - cadmium sulphide - oxidises in the light and becomes the colourless cadmium sulphate.
It can also react with other chemicals and turn into a beige colour, researchers said.
"The results of this study reveal how critical it is to understand not only the chemistry of the discoloured paint, but also the chemistry used to prepare the paints that were available to the turn of the 20th century's most treasured artists," said Jennifer Mass from the University of Delaware in US..