ART AND OPTICS CONVERGE TO PRESERVE FRESCOS:
REFLECTED INFRARED LIGHT UNLOCKS NEW DETAILS OF RENAISSANCE PAINTINGS
WASHINGTON, June 18—When restoring damaged and faded works of art, artists often employ lasers and other sophisticated imaging techniques to study intricate details, analyze pigments, and search for subtle defects not visible to the naked eye. To refine what can be seen during the restoration process even further, a team of Italian researchers has developed a new imaging tool that can capture features not otherwise detectable with the naked eye or current imaging techniques.
The system, known as Thermal Quasi-Reflectography (TQR), is able to create revealing images using reflected light from the mid-infrared part of the spectrum (3-5 micrometers in wavelength). Researchers from the University of L’Aquila, the University of Verona, and Italy’s National Institute of Optics in Florence successfully demonstrated the TQR system on two famous works of art: the Zavattari frescos in the Chapel of Theodelinda and "The Resurrection" by the Italian Renaissance artist Piero della Francesca. The researchers detail their work in a paper published today in the Optical Society’s (OSA) open-access journal Optics Express.
Thermography, the traditional infrared imaging technique in this part of the spectrum (greater than 3 micrometers) detects subtle temperature differences due to the pigmentation on the surface of paintings. These thermal maps can be used during art restoration to reveal internal defects that are not evident in visible light.
In contrast, the TQR imaging system uses a very different tactic and doesn’t detect heat emitted from paintings at all; in fact it tries to minimize it: The TQR system shines a faint mid-infrared light source onto the surface of the painting and records the light that is reflected back to a camera.
"This is, to the best of our knowledge, the first time that this technique has been applied on artworks," said Dario Ambrosini of the University of L’Aquila in Italy, one of the paper’s authors. "This novel method represents a powerful yet safe tool for artwork diagnostics."
All objects emit some infrared radiation. Depending on their temperature, certain materials shine more brightly in one wavelength than in others. At normal room temperature (20° C or 68° F), paintings typically emit more energy in the longer infrared wavelengths (42 percent) than they do in the mid-infrared (1.1 percent).