The New Da Vinci Code: Detecting Hidden Artworks with Terahertz Rays

Ever wondered about hidden Renaissance frescoes? Optical engineering researchers at the University of Michigan, Ann Arbor, describe a novel imaging technique. This innovation could allow art historians to see murals previously hidden under coats of plaster in century-old churches. The finding is published in the February issue of Optic Communications.

This study used "T-rays,"or pulses of terahertz radiation, to investigate century-old paintings. These T-rays are comparable to the X-rays that enable doctors to view the bones under our skin.

"Terahertz is a strange range in the electromagnetic spectrum because it's quasi-optical. It is light, but it isn't," explained Bianca Jackson, first author of the paper who is a doctoral student in applied physics at UM.

This research uses a device combining electronics and lasers. Developed by the Ann-Arbor based company Picometrix, the T-Ray™ system emits pulses of terahertz radiation. T-rays work by permeating the plaster and reflecting back when it collides with a change in the material. Depending on the different colors of paint or the presence of graphite, the rays retain a tell-tale amount of energy when they bounce back. Then, a receiver quantifies this energy so that scientists can produce an image of what lies beneath based on the data, Jackson elaborated. Terahertz imaging is an especially innovative technique since the emitted T-rays do not possess enough energy to knock electrons off atoms, unlike x-rays. Therefore, it prevents the formation of charged particles that could damage the artwork.

"It's ideal that the method of evaluation for historical artifacts such as frescoes and mural paintings, which are typically an inherent part of a building's infrastructure, be non-destructive, non-invasive, precise and applicable on site. Current technologies may satisfy one or more of these requirements, but we believe our new technique can satisfy all of them," added John Whitaker, an author of the paper who is a research scientist and adjunct professor in the Department of Electrical Engineering and Computer Science at UM.

Recently, the team of researchers, including investigators at the Louvre Museum, Picometrix, LLC, and University of Michigan, used terahertz imaging to detect various colored paints and a graphite picture of a butterfly through a thin layer of plaster. In March, the researchers will work in conjunction with French archeologists to examine a mural recently discovered behind five layers of plaster in a 12th century church. Terahertz imaging offers an exciting opportunity for art historians and optical researchers to combine efforts in analyzing the regime changes in Europe that often resulted in artworks being plastered or painted over, said Gèrard Mourou, another author of the paper. He added, "And Leonardo da Vinci's The Battle of Anghiari, for example, is believed to lurk beneath other frescos at the Palazzo Vecchio in Florence, Italy."

Written by Maria Huang

Reviewed by Muhammed Ziadh

Published by Pooja Ghatalia.

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