With a new, gentle method, even the thinnest pigment layers on old paintings can be identified. This could, for example, help to verify the authenticity of works of art, writes a group led by david citrin of the georgia institute of technology in atlanta (georgia, u.S.A.) in the journal "scientific reports".
Using a combination of terahertz spectroscopy and a special mathematical method, researchers were able to determine the layered structure of a painting from the 17th century. Century determine. A german expert is impressed by the study.
"Pictures taken before the age of 18. The paintings, which were made in the nineteenth century, have been difficult to study because their layers of paint tend to be thin," citrin is quoted as saying in a release from his institute. In the case of the painting "madonna in preghiera" from the workshop of the italian master sassoferrato, the scientists discovered five layers: a base layer, a so-called imprimatura, an underpainting, the actual painting and a varnish layer. All layers were on average less than 0.2 millimeters thick, imprimatura, underpainting and varnish even less than 0.04 millimeters.
However, at a larger spot next to the madonna’s head, the paint was 96 micrometers thick. Researchers discovered a restoration that was previously unknown. This would not have been possible from the raw data of the terahertz scanner alone, as it cannot display objects smaller than 0.1 millimeters. The special mathematical approach makes it possible to distinguish between layers as thin as 0.02 millimeters, the scientists write.
Terahertz radiation is used, for example, in body scanners because, unlike x-rays, it can be used safely for biological and medical purposes. It can also be used for non-destructive material testing or painting analysis. For other imaging methods, from electron microscopy to infrared spectroscopy, small samples usually have to be taken from the object under investigation.
The terahertz scanner emits extremely short light pulses, the even shorter reflections are registered. Delays in the running time of light of a few picoseconds (trillionths of a second) can be distinguished. The reflections occur at each boundary surface in the painting, so that the layers in the image become visible. "This will allow us to obtain information that art historians have not had before, and we can provide information that can be helpful for the preservation and restoration of these old paintings," says co-author alexandre locquet.
Michael panzner of the fraunhofer institute for materials and radiation technology in dresden, who was not involved in the study, speaks of "impressive results". He himself used terahertz radiation to screen murals back in 2010. "The new thing about the method is the special mathematical treatment of the measurement data," says panzner about his colleagues’ study. Citrin and his team write that the mathematical method was originally developed to find oil fields in the ground.