Ever wondered what lies beneath classical paintings? What mistakes were covered up, which features were clumsily re-touched, and which ones have faded with time? To better answer these questions, a team from the University of L'Aquila, the University of Verona, and Italy's National Institute of Optics in Florence have added a new imaging tool to the armoury of the art conservationist.
One of the many techniques currently available for this purpose is thermography. This technique detects the thermal energy that is naturally emitted by a painting in the infrared part of the optical spectrum, which is beyond the range visible to the naked eye. Differences in the energy emitted can be caused by differences in the pigments of the paints. These differences can then reveal what lies beneath the top layer of a painting.
The new imaging tool works in the opposite way to standard thermography. While the standard approach measures light emitted by the painting, the new technique, known as thermal quasi-reflectography (TQR), measures light reflected from it. To illuminate the painting, an under-powered lamp is used to minimise the thermal energy emitted by the painting due to heating, which could interfere with the new technique. In addition, because the pigments used for painting normally emit most of their thermal energy in the long-infrared part of the spectrum, the lamp illuminates the painting with mid-infrared light, where thermal emissions are much lower.
When compared with other techniques applied to famous paintings such as “The Resurrection” by Piero della Francesca, TQR made brand new features visible for the first time, such as previously unseen restorative work and overlapping painting techniques for the same part of the picture.
This technique can help art conservationists to better restore these important paintings, using techniques sympathetic to those used by the original painters. The use of reflected light also opens up a brand new area of research for future diagnostic techniques.
Image ©2012 Optical Society of America
Posted on Thursday, 12th July, 2012