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Terahertz radiation helps art restorers in their detective work

22 November 2012

Damaging biocides can be detected on old wooden sculptures, hidden wall paintings can be made visible again and pieces of art analysed using terahertz scanners.

The terahertz scanner not only finds hidden wall pictures, but can also prove the presence of biocides on pieces of art (photo credit: HfbK)
The terahertz scanner not only finds hidden wall pictures, but can also prove the presence of biocides on pieces of art (photo credit: HfbK)

Using terahertz scanners restorers will soon be able to identify quickly, and completely non-destructively, what is happening with an object of art, thanks to recent work by Fraunhofer researchers.

According to Michael Panzner of the Fraunhofer Institute for Material and Beam Technology IWS in Dresden, the special thing about the terahertz (THz) scanner is that, compared with traditional processes, such as X-ray scanners, it works without causing any damage whatsoever. In addition, it  does not require a special permit, as in the case of X-ray inspections. 

The scanner only generates a radiated power of less than 1µW, compared with mobile phones that emit up to 2W.

The process provides concrete data on the structure of the individual layers or of potential hollow areas. In this way the device can also identify areas of repair that provide valuable clues for restorers.

The researchers use short electromagnetic pulses that penetrate the various materials almost without attenuation, whereby some materials display characteristic absorption lines, which can be used to identify them clearly.

In order to overcome some early limitations of the technique, the researchers modified the THz optics with the help of colleagues at the Fraunhofer Institute for Physical Measurement Techniques IPM. The application spectrum of the scanner was also expanded.

IWS, together with partners, now wants to set up a project with the aim of examining the possibilities and limitations of using the THz technology to detect organic biocides. In contrast to the current X-ray fluorescence analysis, which works on an element-selective basis, THz scanners recognize substances on the basis of molecular bonding. Organic biocides, in particular, could be differentiated in such a way.

This also opens up the possibility of undertaking these (normally laboratory based) tests on-site using a mobile scanner. However, a more research is still required until small, portable devices are available that are suitable for such purposes.

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