T-Rays help uncover hidden art

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Scientists are using T-Ray technology in a new way-to help uncover murals that have been hidden under layers of plaster or paint in old buildings.

T-Rays (which are pulses of terahertz radiation that were previously used in space shuttle devices) have now been applied to this new technology by a team of researchers that includes scientists at the University of Michigan and the Louvre Museum.

Their findings are published in a paper entitled "Terahertz imaging for non-destructive evaluation of mural paintings," in the February 2008 edition of Optics Communications.

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

The device used for this research is a hybrid between electronics and lasers. It was developed by the Ann-Arbor based company Picometrix. It's called the T-RayTM system, and it uses pulses from an ultra-fast laser to excite a semiconductor antenna, which in turn emits pulses of terahertz radiation.

The rays permeate the plaster, and some reflect back when there is a change in the material. When they bounce back and how much energy they retain depends on the material they hit. Different colors of paint, or the presence of graphite, for example, cause tell-tale differences in the amount of energy in the returning waves. A receiver measures this energy, and the scientists can use the data to produce an image of what lies beneath, Jackson explained.

According to this article, the ideal requirements for devices that evaluate historical artifacts are that they must be non-destructive, non-invasive, precise and applicable on site. Current methods of imaging underdrawings have limitations. They rarely satisfy all these requirements and certain art materials, such as graphite or sanguine, a red chalk that some of the masters are believed to have used, cannot be detected by them. The researchers believe that T-Rays can reveal the artwork without harming it because, unlike X-rays, T-rays are non-ionizing and therefore not potentially harmful.

They also believe that this technology will be especially important in Europe. In France alone, for example, you have 100,000 churches that may contain artworks that, over the years, have been plastered or painted over. In March they plan to take their equipment to France to help archaeologists examine a mural they discovered recently behind five layers of plaster in a 12th century church.

Like 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. (Credit: Image courtesy of University of Michigan)

Excerpts in this post were taken from University of Michigan (2008, February 5). Hidden Art Could Be Revealed By New Terahertz Device. ScienceDaily. Retrieved

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Wow, I had never heard of T-rays before. Crazy! I remember walking in Rome and seeing many partially exposed tile murals on the floors of some of the ruins. I wonder if this technology could be used to see the works under all the dirt. dust and grime. I also wonder if we could see the details under ash and if it could be used find bodies in wreckage or volcano explosions.

Dear Kevin Z, Thank you for your comment.

"I also wonder if we could see the details under ash and if it could be used to find bodies in wreckage or volcano explosions."

From what I understand, depth penetration is quite a problem for T-Ray imaging. For example, the 3D T-Ray imaging system called the TPITM imaga 1000 (manufactured by TeraView) has a depth penetration of approximately 3 mm while other devices can reach up to 7mm. Depth penetration in the mm range would be rather insufficient to identify bodies trapped under wreckage or volcanic explosions.

KevinZ said: "Wow, I had never heard of T-rays before. Crazy!"

Kevin, they're usually just called "extremely high frequently radio waves" on your textbook illustration of the electromagnetic spectrum (part of the microwaves), but that name doesn't sound spiffy enough when a company develops an expensive imaging system to try to sell to medical and security firms -- "T-rays" has a much better "Gee Whiz!" factor (GWF). And since they are basically just microwaves, their penetration depth is shallow (this initial study found an image under only 4 mm of plaster) and will never approach other electromagnetic surveying techniques or ground-penetrating radar, which is what'll you'd need to look through meters of ash. It is an interesting technique but useful for only a narrow set of problems.