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Wednesday, August 08, 2007

Original or fake? Infrared to detect imitation art

Screening paintings (left) with infrared light reveals the watermarks (right) of the paper mills. These enable works to be dated and examined for authenticity without risk of damage


Recovered paintings of the famous Dutch artist Rembrandt have a unique feature about them: Experts are never really sure which ones he created himself.

Many of the paintings, etchings and drawings attributed to the artist were actually created by his pupils.

And to add to that, several other works - attributed to him - were actually painted by imitators, many decades after the master’s death.

These imitations are so brilliant, that at times, it is even difficult for art historians to distinguish the original works of art from the fakes.

However, German research scientists at the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut (WKI), in collaboration with colleagues from the TU Braunschweig, have developed a simple way of exposing fake paintings.

The new method screens the pictures with infrared radiation, which exposes the watermarks of the paper mills, thus allowing researchers to date the works without risk of damage.

The watermarks in the paper were woven into the wires of the screen moulds that were used to scoop paper fibres out of the pulp.

“Every paper mill had several different watermarks at any one time - often a different one on each screen mould,” says WKI project manager Peter Meinlschmidt. “We know a lot about which watermarks were used by which paper mill at which period of time.”

Paper can be dated even more accurately by studying tiny changes in the watermarks that were caused as the screen moulds progressively wore out.

Art historians usually hold the drawings against the light to see the watermark. However, the marks are often obscured by ink, handwriting and paints on the front and back of the painting to the point where they are indecipherable.

The former solution was to trace them, which may leave pressure marks on the picture.

X-rays also reveal the watermark, but the X-ray technique is not usually possible in museums for technical reasons and for the sake of radiation protection.

On the other hand, it is risky to remove the works of art from their air-conditioned environments and take them to a laboratory.

“Most inks are transparent in infrared light,” says Meinlschmidt, explaining the crucial feature of the new method. “So we put a warm plate with a temperature of 35 to 40 degrees Celsius behind the picture and use an infrared camera to register how much heat the picture allows to pass through. This shows up the differences in paper density, and thus also the watermark.”

This exposure to heat is perfectly safe for the picture: As it is placed at a distance of one centimetre from the hot plate for the duration of only one second, it absorbs less heat than if it were touched briefly by someone’s fingers.

The Bavarian State Library in Munich is considering using this method to file the watermarks with the respective pictures in its digital archive.
posted by strangebeauty at 9:06 AM

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