New Light Technique Reveals Hidden Details of Historic Paintings

A painting hanging on a wall may tell one story, but what lies beneath may tell quite another. Scientists have created a new instrument that's capable of capturing subsurface details from artwork at a high resolution.

Great masterpieces of western art, such as a Rembrandt or a Leonardo, are covered with varnish. In fact, sometimes several coats of it are applied at different parts over their history in order to protect the paint underneath. Over centuries, though, this varnish can degrade; conservators carefully clean off the old varnish and replace it with new varnish. In order to do this safely, though, it's useful to understand the materials and structure of the painting beneath the surface.

Now, researchers are using non-invasive imaging techniques to study paintings. Optical Coherence Tomography (OCT) was original developed for medical imaging, but has now been applied to art conservation. It uses a beam of light to scan the intact painting without removing physical samples. In this latest study, though, the scientists gave OCT an upgrade.

The scientists used a broadband laser-like light source. The wider frequency range allowed for a more precise data collection, but such light sources were not commercially available until recently. The addition of the broadband light source enabled the apparatus to scan paintings at higher resolutions.

"We were able to not only match the resolution but also to see some of the layer structures with better contrast," said Haida Liang, leader of the project, in a news release. "That's because OCT is particularly sensitive to changes in refractive index."

The new technique could be huge when it comes to art restoration and also preservation. The non-invasive methods are a big step forward in terms of future art preservation.

The findings are published in the journal Optics Express.

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