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T-Rays Reveal Hidden Art Harmlessly

Source: Discovery News www.discovery.com.com by Eric Bland

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.

Different wavelengths of T-rays are absorbed or reflected by different materials. By looking at when and which wavelengths are reflected or absorbed, researchers see what a piece of artwork is hiding.

"The timing of the T-rays is critical," said Whitaker. "Without it you can't distinguish the depth. It's something like a pulsed radar."

There are currently two T-ray machines the researchers use to examine art. The first is a stationary machine at the University of Michigan. The other is a portable one the size of a breadbox from Picometrix, a company founded by a former University of Michigan faculty member.

Right now the T-ray images appear only in black and white. The next step is generating full color images of buried artwork.

"The potential of this technique is very exciting," said Daniel Mittleman, a professor of Eletrical and Computer Engineering at Rice University who does T-ray research but was not involved in the Michigan study.

T-rays won't eliminate the need for other imaging techniques, he said, but will instead "be a complimentary technique that will reveal new information."