What lies beneath?

Just as X-rays let doctors see the bones beneath our skin, 'T-rays' could let art historians see murals hidden beneath coats of plaster or paint in centuries-old buildings, University of Michigan engineering researchers say.

T-rays, pulses of terahertz radiation, could also illuminate pencilled sketches under paintings on canvas without harming the artwork. Current methods of imaging underdrawings can not detect certain art materials such as graphite or sanguine, a red chalk that some of the masters are believed to have used.

The team of researchers, which includes scientists at the Louvre Museum, Picometrix and the University of Michigan, used terahertz imaging to detect coloured paints and a graphite drawing of a butterfly through 4mm of plaster. They believe their technique is capable of seeing even deeper.

In March, the scientists will take their equipment to France to help archaeologists examine a mural they discovered recently behind five layers of plaster in a 12th century church.