T-Rays Reveal Hidden Art Harmlessly

Feb. 7, 2008 -- Forget X-rays. Scientists from the University of Michigan are using T-rays, a benign form of electromagnetic radiation, to see artwork hidden for centuries by paint or plaster.

"It would be an overstatement to say it's the best way to look through materials," said John Whitaker, professor of electrical engineering and computer science the University of Michigan and one of the authors of the study appearing in the current issue of Optics Communications. "But we can see underlying material that other scans miss."

T-rays have been around for decades and used for everything from space shuttle foam analysis to poison detection. But this is one of the first times they have been used in the art world. The researchers plan to apply the technology next month to find murals hidden beneath layers of plaster in centuries-old churches in France.

Unlike energetic and potentially harmful X-rays, T-rays, or terahertz rays, are completely benign to living things. Since many paint dyes are organic, and thus susceptible to X-rays, T-rays are better for imaging artwork because there is no risk of damaging the piece. The new technique should be able to detect particular dyes in old artwork, such as sanguine, a reddish-brown color that Flemish painters often used.

To generate T-rays, the scientists shoot a special laser beam into an electromagnetic field. When the laser hits the field it's like "turning on a light switch," explained Whitaker, and the T-rays shoot out in pulses toward the target.