Looking into the depths of a masterpiece without scraping the surface

When art experts restore or conserve paintings, they have to know what they’re getting into. Old Master paintings are usually varnished, often several times at various points through their history; although originally intended to protect the surface of the painting, the varnish can degrade, dulling the colours. An important stage in conservation is removing the old varnish, but to do this the conservators must understand the layers of material that make up the picture: how many coats of varnish, of what composition; and what the various layers of paint in the picture actually are. Generally, this is done by taking tiny samples from the picture — around a quarter of a millimetre across — and analysing them. Optical specialists at Nottingham Trent University have now worked with the National Gallery to upgrade a technique that can look below the surface of an Old Master without damaging it; it could also be used to study old documents, they say.