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Raman probe sheds light on old map

31 Jul 2002

Tell-tale spectroscopy of pigments showing 'America' in a Viking map backs up claims that it is a 20th-century forgery.

One of the world's most famous and controversial maps is a fake, according to UK scientists who have studied it using Raman spectroscopy.

Katherine Brown and Robin Clark, from University College London (UCL) have been analyzing the Vinland Map - a map of the world that some claim originates from the mid-15th century.

Crucially, the Vinland Map includes representations of Iceland, Greenland and the north-eastern seaboard of North America, called "Vinland". Its proponents claimed that the map had been drawn around 1440 - half a century before the legendary trips made by Columbus and Cabot.

Brown and Clark used a Raman microprobe from UK company Renishaw to do the analysis. It incorporates a helium-neon laser operating between 0.5 and 5 mW, with a spot size of 5 micron focused by a 10 x lens. The laser light is delivered to the sample via a fiber-optic probe.

By using Raman spectroscopy, the valuable document can be probed without the need to remove samples of material.

Features on the map consist of black ink and an underlying yellowish line. In their analysis, Clark and Brown found that yellow areas contained anatase - a form of titanium dioxide that is rarely of natural origin.

Anatase could not be synthesized until the 20th century, prompting them to conclude that; "The presence of a yellow line containing anatase, closely associated with a stable carbon ink, indicates that the Vinland Map is a modern forgery."

"Knowing that yellowing is a common feature of medieval manuscripts, a clever forger may seek to simulate this degradation by including a yellow line in his rendering of the map," they added.

"The Raman results provide the first definitive proof that the map itself was drawn after 1923," Clark said.

The work is described in the current issue of the journal Analytical Chemistry, published by the American Chemical Society.

Michael Hatcher is technology editor of Opto and Laser Europe magazine.

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