High tech help for Indiana Jones

New method allows a view into the interior archaeological finds

Replica of a brooch for the Ancient Charm Project © AG Kirfel, Uni Bonn
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Researchers fill small metal cubes with roof bones and "fake" century-old pieces of jewelery - all for science: They want to develop a method with which they can look into the interior of valuable archaeological finds and historical works of art, without destroying them.

The fake is documented little by little, from the first sketches to the finished ornate brooch. The "counterfeiters" themselves are noticeably proud of their work. "It looks very lifelike, right? Even if, instead of a real pearl, we took a synthetic one out of the DIY store ", explain the crystallographer Professor Armin Kirfel and the head of the precision mechanics workshop Herbert Phiesel from the University of Bonn.

Phiesels and Kirfels employees at the Mineralogical Petrological Institute have made the replica of gold, silver, copper, iron and an almandine crystal. The immeasurably valuable model is stored in the Hungarian National Museum in Budapest. More than fourteen hundred years ago, the brooch may have graced the breast of a Merovingian prince. The researchers are still wondering how the piece of jewelery was made exactly.

Project "ANCIENT CHARM"

Scientists from five European countries are currently trying to answer this question. In Germany, the universities of Cologne and Bonn are involved in the project called "ANCIENT CHARM". But this is about more: The project partners want to develop a new method to look into the interior of valuable archaeological finds or art historical objects, without damaging them in the least. The EU promotes cooperation with almost two million euros; She is coordinated by the University of Milan.

Workshop manager Herbert Phiesel (left) and Professor Armin Kirfel fill a "black box". © AG Kirfel, University of Bonn

"We want to examine the pieces with different methods and thus construct a three-dimensional image in the computer, from which the inside of the finds, that is their material composition, can be seen in detail, " explains Kirfel. For example, pieces of jewelery such as pearls used to be given a layer of clay to make them look more unsightly and not stolen. Weapons were decorated with gold or silver, but what was their core, and how were they merged? How did you lock holes in bronze containers, and what did you take as a piece of work? display

Already today, archeologists are bombarding their finds with rays in order to get to the bottom of their secrets. "ANCIENT CHARM" now wants to combine several processes and thus overcome the disadvantages of the individual methods: with high-energy X-rays, it is possible, as with neutrons, to illuminate thicker layers of material. "You only get contrasts that indicate that the material changes there, " says Kirfel. "What material it is, is not obvious only with these methods."

Atoms as diffraction aids

There are additional ways to do this: If the researchers bombard archaeological finds with neutrons, for example, they can excite the atomic nuclei in the object under investigation. "The find then emits gamma radiation, from which one can conclude on the chemical elements that are present at this point, " explains the Bonn crystallographer. From the way in which the neutrons are diffracted at the atoms in the material, one can also obtain information about its composition and microscopic structure.

That sounds more martial than it is. "The object is not damaged, " says Professor Kirfel. However, the scientists do not take any risks: before they let go of their tomographic and spectroscopic methods on irreplaceable originals, they first test them for copies. That is also the reason why Kirfel and his employees act as "forgers".

Metal cube with rambling content

The Bonn mineralogists also put their competitors to the test in a different way: they build (as do colleagues in Hungary) so-called "black boxes" - metal cube of five centimeters edge length, which they fill with different materials in different arrangements. Their project partners are now to find out how these "offal" are designed - solely by applying the various non-destructive fluoroscopy methods.

In doing so, Kirfel and his colleagues go to work with some imagination: One of the dice, for example, contains the thighbone of a badger, wrapped in leather and surrounded by a shell of wood. Kirfel does not want to disclose any details about a particular difficult nut to crack in the hands of her project partners - after all, the examinations of the 10 Bonn boxes have not yet been completed. "Only so much: We have embedded very different objects in a filler that contains hydrogen, " says Kirfel. "Hydrogen makes the neutron transillumination difficult and causes a strong background dispersion - that is a special challenge."

(idw - University Bonn, 18.09.2007 - DLO)