text: Vincent van Gogh has a good claim to be the greatest colourist ever. His yellows, his blues, his cherry trees and sunflowers and skies all created through thickly impastoed smears of chromatic splendour have made the very name Van Gogh synonymous with intense expressive colour. 
   
   Yet some of the colours we see in Van Gogh's paintings are just pale echoes of the hues he originally set down in the 1880s. This startling discovery has just been revealed by the Van Gogh Museum in Amsterdam. A research project undertaken by the museum reveals that a number of Van Gogh's favourite paints have faded badly and changed the appearance of his works, making them milder, more empty, less exquisite in their use of complementary colours than they were when he painted them. 
   
   The evidence is presented in Van Gogh at Work, a new exhibition at this popular and intellectually rigorous museum examining his practice as a painter, and looking at everything from the kinds of canvas he used – Van Gogh painted on everything from raw jute to, when he was short of cash, a dishcloth – to his intimate exchanges of ideas with friends such as Gauguin and Toulouse-Lautrec. 
   
   The friendship with Toulouse-Lautrec is a touching example of how a physical examination of art can lead us closer to the artist. Van Gogh knew the great painter of Montmartre nightlife when they both lived in Paris, but evidence presented here, including the fact that they bought their canvases at the same shop, shows them working closely as colleagues. 
   
   Another intimate revelation about Van Gogh's working habits is that he regularly reused his canvases, painting over early works. A flower painting in the show has a painting of wrestlers by Van Gogh concealed under it. When he wanted to keep a painting, he sometimes painted on the back: two brown studies for his early work The Potato Eaters have later, vibrant self-portraits on their reverse. 
   
   Amid all this insight, the fact that Van Gogh's colours are not always in their pristine glory is hard to assimilate. The evidence is relentless. This exhibition is in effect a public report on a massive research project using the latest, non-invasive techniques to study the microscopic structure of art. You can even look through an electronic microscope for yourself in an interactive that lets you see the grains of dirt in Van Gogh's rich strokes of oily colour. 
   
   In the end, the fact that some of Van Gogh's colours have changed over the years is simply a homage to his genius. No one, after all, has any complaint about his colours. In this exhibition, I stood enraptured by the deep blue sky and golden street in his 1888 painting The Yellow House. 
   
   It doesn't matter, for most of us, if there are changes in his colours. His visionary art is such that it can evolve and still be true to itself. The fresh insights in this brilliant exhibition, which includes a loan of Van Gogh's Sunflowers, no less, from London's National Gallery, do not undermine the artist's greatness. They just bring us closer to him, as we stand at his shoulder, watching him work – until we are really close, in a fresh, invigorating way, to his material life as an artist. It even includes his palette, smeared with colours, and three tubes of paint that belonged to him. They are exhibited next to his self-portrait. 
   
   His eyes in the portrait are formidable – they will never fade. ||||| The reds in Van Gogh's Wheat stack under a cloudy are slowly turning white © Peter Horree/Alamy 
   
   The vibrant red leaves on the pond in Vincent van Gogh ’s Wheat stack under a cloudy sky are slowly transforming into the colour of the clouds above. Now, scientists in Belgium may have found the missing chemical link to explain why these reds are turning white 
   
   During his most prolific period, Van Gogh produced 2000 paintings over a decade and was known for his use of intense colours, which, some say, reflected his complex personality. However, many of the painter’s most celebrated works have been degrading due to exposure to light. 
   
   ‘Normally, the idea is these paintings are there for a hundred years, or five hundred years, and they’re static – nothing really changes,’ says Koen Janssens from the University of Antwerp, Belgium. ‘But the opposite is actually true when you look in detail.’ 
   
   Red lead or minium (Pb 3 O 4 ), thought to be one of the earliest synthetically produced pigments in antiquity, was used extensively by Van Gogh in his paintings. Scientists have known that minium ‘whitens’ under light but have not been able to determine why. 
   
   The white degradation product that forms around the red paint is an exotic lead mineral © Wiley-VCH 
   
   To understand this process, Janssens and his colleagues examined a minute white globule taken from the surface of the pond in Van Gogh’s 1889 piece a Wheat stack under a cloudy sky using x-ray powder diffraction tomography. By firing a focused beam of x-rays at the sample from different positions, they were able to gather information on the chemical species present. 
   
   ‘[It is] an enclosed little world,’ explains Janssens. ‘The minium is changing and the products [are] captured below the surface of the paint.’ He goes on to add that the red lead is at the grain’s centre and, over the years, it has become coated with degradation products. 
   
   ‘Starting from minium, we found plumbonacrite (3PbCO 3 .Pb(OH) 2 .PbO), which is a very exotic mineral of lead,’ says Janssens. ‘More towards the outer parts of this sample we found the more commonly known carbonates, hydrocerussites (2PbCO 3 .Pb(OH) 2 ) and cerussites (PbCO 3 ).’ 
   
   The cerussites are a family of compounds that form the white outer shell around the minium but plumbonacrite has never been detected before in a pre mid-20th century painting. Janssens calls this rare mineral the ‘missing link’ and the team are now able to propose a chemical pathway for the photochemical degradation of minium. The researchers think that when red lead is exposed to light it is converted into plumbonacrite, which reacts with carbon dioxide to form hydrocerussite and cerussite. 
   
   ‘It’s a very important [piece of research],’ says Philippe Walter, director of the Laboratory of Molecular and Structural Archaeology in France. ‘For the conservation of works of art, it is important to look at this phenomenon to be sure to take care about the quantity of light [in museums].’
target: – Look at a Van Gogh painting today, and you're not quite getting the full effect. Reports in 2013, as cited in the Guardian, revealed that the paintings were fading; studies have found yellows are turning brown. The color red is also posing a problem in works like Wheat Stack Under a Cloudy Sky, and researchers are now moving closer to finding out why, Chemistry World reports. Van Gogh often used a pigment known as red lead. The stuff, also called minium, turns whiter when it's exposed to light. Seeking to understand the process, researchers analyzed a tiny dot of paint from the work. The process, which involved shooting X-rays at the paint, showed that the red lead is now covered with what Chemistry World calls "degradation products" in the form of other chemicals. The researchers found a substance they call the "missing link" in the degradation process: It's a mineral lead known as plumbonacrite, Hyperallergic reports. Light shining on the plumbonacrite has apparently caused the buildup of other chemicals. Interestingly, as Hyperallergic notes, the researchers say plumbonacrite has never before been reported "in a painting dating from before the mid 20th century." Of course, the color issues actually make Van Gogh's work even more impressive, Jonathan Jones wrote in the Guardian: "In the end, the fact that some of Van Gogh's colors have changed over the years is simply a homage to his genius. No one, after all, has any complaint about his colors." Last year, Van Gogh—or rather, his "regrown" ear—made some unusual headlines.