trois hommes frescoAirport scanners can see more than your underwear. Terahertz spectroscopy, the imaging technology used in airport body scanners, has uncovered a hidden, ancient fresco underneath a wall painting at the Louvre.

Terahertz spectroscopy uses beams of electromagnetic radiation that lie between microwaves (used in kitchen ovens) and infrared rays (used in TV remotes) on the spectrum. These waves are known for their ability to examine materials without damaging them, unlike X-rays and ultraviolet light, and are commonly used in other areas like biomedical imaging and pharmaceuticals.

While using this technology to examine a painting, Bianca Jackson, a postdoctoral research fellow at the University of Rochester, found evidence of another painting underneath.

“We were amazed, and we were delighted,” she said during a presentation to the American Chemical Society. “We could not believe our eyes as the image materialized on the screen. Underneath the top painting of the folds of a man’s tunic, we saw an eye, a nose and then a mouth appear. We were seeing what likely was part of an ancient Roman fresco, thousands of years old.”

The ‘he” referred to is Giampetro Campana, a 19th century Italian art collector who assembled an impressive collection of Greek, Roman, and early Italian artwork. Back then, it was common practice for artists to paint over existing works of art, either because they could not afford new canvases or because patrons commissioned new artwork to cover up older or unsuccessful pieces. Researchers had reason to believe that Campana commissioned Trois hommes armes de lances to go over another image.

Initially, the team tried using x-ray radiography  and x-ray fluorescence to find out what secrets lurked beneath. However, it wasn’t until they tried terahertz spectroscopy that the original artwork peeked through.

“No previous imaging technique, including almost half a dozen commonly used to detect hidden images below paintings, forged signatures of artists and other information not visible on the surface has revealed a lost image in this fresco,” Jackson said. “This opens to door to wider use of the technology in the world of art, and we also used the method to study a Russian religious icon and the walls of a mud hut in one of humanity’s first settlements in what was ancient Turkey.”

Photo Credit: J. Bianca Jackson, Ph.D. and Dominique Martos-Levif