Jürgen Kolz stares at his screen. The engineer at the Technical University in Aachen is examining a fresco that has been sent in by New York's Metropolitan Museum of Modern Art. In front of him sits the world's smallest, mobile magnetic resonance tomograph (MRT).

It's about as big as a conventional laser printer. A sensor that's not thicker than a finger moves towards the fresco and stops just milimeters in front of the fresco. Now the real work can begin.

"We're choosing a certain point in the fresco that we want to examine and measure the specimen in various depths," Kolz says. "The signal then gives us information about the kind of colors that were used, the thickness of the different layers and the stage of the ageing process."

No more damage to art

Art experts and restorers find this information immensely valuable. The big advantage of this kind of test is that a fresco does not have to be damaged.

So far, microscopically small probes had to be removed to examine them -- a process that doesn't make art lovers happy. The MRT in Aachen does away with this. While large museums already use scanning methods, Kolz says that his method is superior as it can determine the age of the colors as well.

The ability to determine the age of paint layers is a valuable tool for museums. Bernhard Blümich, who heads the teams of researchers in Aachen, soon realized that the method could also be used to distinguish between originals and forgeries.

Recreating lost paintings

But the new technique's advantages go beyond catching forgers.

"We can examine the various layers of a painting or fresco," said Federico Casanova, a member of the team of researchers. "That way we can see if there are other paintings below the surface."

In the future, the researchers will be able to reconstruct these submerged paintings by "rebuilding" them on a computer and creating a perfect copy. The art world has already expressed interest. Aachen researchers have already scanned several frescoes and paintings in the Italian town of Perugia. They will also travel to London at the end of the month to convince art experts at the National Gallery that they should employ their method as well.