Researchers are investigating how the Dutch painter achieved his vibrant colours. Sanjida O’Connell reports

The Times - Monday August 12 2002

The paint is in thick, creamy whorls, almost slathered on, the turquoise and ultramarine in the cloudy sky mirroring the wind spiraling through the heavy gold of the cornfield. Tall, conical cypresses to one side are such a dark green they’re almost black, the paint smeared in short, heavy daubs. Up close Vincent Van Gogh’s Cornfield with Cypresses is, like most of his paintings, heavily textured. But the rich yellows and vibrant pinks Van Gogh is known for have faded. Scientists are now trying to recreate the paint he used over 150 years ago. Finding out exactly how Van Gogh mixed his paint could help conservators restore ailing paintings, as well as helping galleries detect fakes.

“We think of him as having very thick and waxy paint, but when you look closely, you can see fine drips at the beginning and end of his brush stroke,” says Dr Leslie Carlyle, who is investigating Van Gogh’s painting technique on behalf of the Hart Project (Historically Accurate Reconstructions of Oil Paintings Composites) at the Netherlands’ Institute for Cultural Heritage. “The paint is not as buttery as we expected,” adds Carlyle. In the early nineteenth century artists would have mixed their own paint, but by 1841 artists could buy paint in collapsible metal tubes, just as we do today. Van Gogh relied on his brother, Theo, to buy him paint from France. What Carlyle is trying to find out is whether Van Gogh was able to achieve a range of textures with this paint, or whether he added other substances to it. Artists often mixed in hot oil, as Carlyle discovered when she studied manuals drawn up by ‘Colourmen’, the people who used to supply paint to artists. One recipe required heating oil until it was searing 300oC. This process gives the paint a stringiness because the main component of the paint, usually a metal such as lead oxide, reacts with the hot oil. To achieve a more buttery texture, Van Gogh could have added other chemicals, like lead acetate. Known as ‘sugar of lead’ because it tasted sweet, the chemical is highly poisonous. “Van Gogh may have been aware of how to achieve different effects by using various substances – but we just don’t know,” says Carlyle, “There is no documentary evidence to tell us whether he mixed his own paint."

In order to establish whether Van Gogh altered his paint researchers will need to analyse tiny amounts of paint from his pictures – about the size of a full stop - and subject them to gas chromatography and mass spectrometry. These processes will be conducted in autumn, and Carlyle will then begin the next stage - recreating his paint. In the last half of the nineteenth century, stream driven roller mills were used to grind linseeds and poppy seeds to produce oil to make paint. Because Carlyle wants the process to be as authentic as possible she is having her own small roller mill made so that she can steam press oil. She’ll then grind pigments between two slabs of granite and add the oil. “We’re really doing this to understand his paint,” says Carlyle, who stresses that this paint will not be for sale. “Aside from curiosity, Van Gogh, like many painters, often made many copies on the same theme, and people have questioned whether they are his. By understanding what makes the paint his, we can compare the paint profile between different paintings and prove which ones are authentic.”

Carlyle has already photographed the surfaces of all Van Gogh’s paintings at a 160 fold magnification to see how the paints have altered over time. The chemistry of oil paints changes as the metals and organic material react to the environment – in Van Gogh’s case some of the colours have faded; for instance, the chrome yellow in some of his paintings has become a dirty orange. The paints Carlyle will recreate could help restorer’s make accurate, albeit minor repairs to the paintings, but the overall colour of the paintings will not change. “We don’t believe in changing the colour of the paint because that’s altering the truth,” says Carlyle, “but we could show a computer image of the painting as it used to be.”