Maryam Khojastehfar, who is involved in investigating the painting at DTU Fotonik, is studying photonics as part of the Erasmus Mundus exchange programme. Photo: Joachim Rode

Ultrafast light reveals sketches under Renaissance painting

Monday 25 Sep 17


Peter Uhd Jepsen
Professor, Group Leader, Deputy Head of Department
DTU Electro
+45 45 25 57 11


The painting is scanned in horizontal layers—here we see three of them:

Photo: Joachim Rode

Photo: Joachim Rode

Photo: Joachim Rode

Short light pulses help to reveal secret drawings under the paint of a 16th century art relic. The advanced technology can be used to document key cultural artefacts.

A scanner head runs slowly up and down the exquisite Italian painting ‘Dearth af Adonis’ as we step into the light-sensitive basement under DTU Fotonik. Here, researchers specializing in ultrafast optics are engaged in a rather unusual task.

In the spring, they were contacted by a private art collector—Nick Brincker—via the National Gallery of Denmark. He wanted to know whether carbon markings underneath the colouring layer on one of his pictures were an indication that the painting was the work of the Italian architect, architect theoretician, and painter—Sebastiano Serlio.

The art collector’s task for the DTU researchers was to determine whether the painting concealed architectural drawings, names, or notes. Were this the case, the painting would be worth a great deal of money, and Nick Brincker would then plan to display the painting and free up funds for non-profit social projects in Denmark.

In the past four years, DTU researchers have performed similar studies of paintings—in some cases in collaboration with the National Gallery of Denmark. This has given them knowledge of how a painting is structured and how to separate the layers. But on this occasion, they were dealing with a ‘real life’ task. No one knew what they would find, how it would look, or whether there was anything at all under the paint.

Not just shadows
“We’re thrilled that we can see anything at all. The signs are promising. We’re not just seeing shadows—there are letters, circles with dots, and other geometric shapes,” says Iranian Maryam Khojastehfar, who is involved in investigating the painting at DTU Fotonik and who is studying photonics as part of the Erasmus Mundus exchange programme.

“This tells us that we have a technique that can explore the deeper layers of a painting without damaging it. The results will now be sent to an art historian, who will assess our findings and determine whether the Sebastiano Serlio hypothesis can be confirmed.”

Together with Professor Peter Uhd Jepsen, she has scanned the painting for several weeks using a special laser system that emits light pulses at 100 femtoseconds together with very long wavelengths. A femtosecond corresponds to 10-15 seconds.

The technique is a part of the field of research known as ultra-fast optics, which is based on very short light pulses of remote infrared light. The wavelength of the light is roughly the same size as a pinhead. DTU Fotonik is the only group in Denmark—and one of the few in the world— to use this technique to examine paintings.

Can see all the layers
The light, which is invisible, can shine through the materials—e.g. paint, which normally is impermeable. The light is reflected as small echoes from the four different layers consisting of lacquer, colours, a white foundation, and canvas. On the Italian painting, there is also an extra canvas back, as the picture has been repaired.

Using the echoes, the researchers can define which reflections emanate from which layers. This means that not only can they see the surface of the painting, but also deep inside it. According to Peter Uhd Jepsen, the technique can be used to document our cultural heritage:

“We can get answers concerning the origin of the paintings and whether we are dealing with ‘fakes’. Nowadays, it is possible to paint pictures that are an exact copy of the Mona Lisa. But no matter how much the artists try, they cannot paint the same strokes and recreate the same structure as the original. All this can be exposed using our technique.”

Foto: Joachim Rode

Behind the painting

Nick Brincker purchased the painting in an auction in London in 2010. Here, it was listed as being painted by an unknown artist from the circle around the Italian Renaissance painter Jacopo Zanguidi. In 1930, the painting was sold in New York as the work of an unknown artist from the circle around Antonio Allegri (Correggio).

On the painting, the initials ‘SS’ can clearly be seen, possibly alluding to the architect Sebastiano Serlios. As there are no known paintings by Serlio which can be said with absolute certainty to be by him, there is no basis for comparison.

The painting is believed to have had significance for an astrological/hermetically secret cult that existed in many European countries in the Middle Ages and during the Renaissance.

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