Over the centuries, either to save space or because of changing social mores, many church murals have been painted over. Michael Panzner and other scientists at the Fraunhofer Institute for Material and Beam Technology IWS in Dresden have found a way to use terahertz (THz) radiation to uncover the hidden treasures underneath newer coats of paint.
THz radiation can penetrate multiple layers of paint and lime wash to reveal many consecutive paintings, something other forms of radiation, such as microwaves or UV, cannot do. Unlike more conventional methods, the THz scanner does not damage the more recent top paintings, which are sometimes also valuable.
The scanner consists of two main parts. A femtosecond laser scans over the wall mural, producing short bursts of THz radiation. By the way, a femtosecond is 10 − 15 of a second, so I do mean short. A separate detector scans the same wall picking up the radiation pulses reflected from the wall. Each layer and/or pigment on the wall reflects those pulses differently, and those differences are used to reconstruct the entire art history of that wall.The technique has been successfully tested in the lab. Panzer and his team are eager to try their device, which they’ve dubbed the ‘reveal-all-scanner’, in a church.