X-ray vision uncovers hidden self portrait

A collaboration between scientists and art historians in Australia has uncovered a lost work of art by one of the country's most famous artists. But rather than lying neglected in a dusty attic, this work was hidden under nothing more than a layer of paint.

The use of x-rays to see the unseen is well known. Our own bones absorb x-ray radiation, so medical x-rays can effectively strip away our flesh to reveal our skeletons. In the same way, x-ray radiography has been used to look at works of art, uncovering hidden works where artists have reused their canvasses, painting new over old. 'However, these techniques have their limitations,' says David Thurrowgood, senior conservator at the National Gallery of Victoria, Australia, 'particularly when large amounts of lead or other heavy elements prevent visualisation of the layers underneath.' Unfortunately, such elements are extremely common when artists have applied a white, often lead-based, layer to begin afresh. Conventional radiography is then unable to penetrate the lead-lined tombs of such lost works.

To solve this problem, Thurrowgood and collaborators employed x-ray fluorescence, using x-rays produced at the new Australian synchrotron facility in Melbourne. Exposed to this radiation, the paint fluoresces - each of its component elements emitting a unique signal that can be detected and used to recreate the underlying image. This also enriches the quality of the data says Deborah Lau, one of the collaborators and a programme leader at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Victoria. 'X-ray fluorescence allows an appreciation of the different colours and paint composition,' she explains. The technique was pioneered by Koen Janssens at the University of Antwerp, Belgium, who has used it to reveal hidden works by Vincent van Gogh. Janssens met the group whilst touring Australia to promote the new synchrotron facility, and encouraged their collaboration. 'I visited [NGV and the synchrotron facility] in 2009,' says Janssens, 'and I pointed out to them: in the same place you have a synchrotron and you have a gallery - make use of it.'

The painting in question is a self-portrait by Arthur Streeton, who was, fittingly enough, a native of Victoria.   'Streeton is one of Australia's most loved artists,' says Thurrowgood. 'He painted very few portraits and this was an opportunity to uncover a very rare self portrait.'  The technique also reveals other secrets, he adds. 'In this case, we can see changes in [Streeton's] composition and his painting methodology ... understanding drawn from this painting will impact how we look at other parts of the collection.'

Importantly, the Australian synchrotron facility makes use of a new detector, developed at CSIRO. 'The Maia detector allows rapid data acquisition at the nanometre scale,' says Lau, and this unique instrumental setup enables artistic archaeology in unprecedented detail. 'We have much higher resolution in a fraction of the time when compared to earlier experiments,' says Thurrowgood.  Janssens agrees that the results are impressive. 'The images look as though you were seeing them with the naked eye,' he says. 'I get very excited when I see what they can do.'

These new insights demonstrate that this marriage of science and art is coming of age says Janssens.  'At the moment, we are still in the scientific world, publishing papers on improving the technique,' he says. 'But the first art history papers are now coming out.'