Damaging biocides can be detected on old wooden sculptures, hidden wall paintings can be made visible again and the layered structures of pieces of art analyzed. Using terahertz scanners restorers will soon be able to identify quickly, and completely non-destructively, what is happening with an object of art.
Shortly before leaving the German Democratic Republic the artist, Gerhard Richter, had left it behind as a journeyman‘s project. Then, in the 1960s, it was unceremoniously painted over. However, instead of being interested in the picture, the scientist involved was far more interested in the new detector which was being used for the first time here. Using it, the scientists gained important information about the layered structure of the wall and the structure of the picture area being examined.
According to the scientist, the special thing about the terahertz (THz) scanner is that in comparison 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 harmful X-rays. This is because the scanner only generates a radiated power of less than 1 µW. For comparison: under less than ideal conditions, cell phones emit up to 2 Watts. Furthermore the process, provides concrete data on the structure of the individual layers or of potential hollow areas. In this way the device also indicated in the Hygiene Museum that in one area the plaster on the wall had evidently been repaired - a valuable clue for the restorer.
The scientists used 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 previous tests, however, the system had reached its limits, for example with behind-the-wall paintings on uneven, very structured walls. For this reason the scientists at IWS continued to develop the detector head by modifying the THz optics together with the Fraunhofer Institute for Physical Measurement Techniques IPM. The application spectrum of the scanner was also expanded.
In the future the tests are to be feasible 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. Above all, close communication and cooperation with restorers and monument preservationists is required for the continued technological improvement of the THz measurement system.
This story is reprinted from material from Fraunhofer, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.