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Tuesday, 30 July, 2002, 23:02 GMT 00:02 UK
Fresh doubt over America map
The map: "Vinland" is on the left edge
More doubt has been cast over a supposedly medieval map of America drawn up prior to the voyage of Christopher Columbus.

Many scientists believe the so-called Vinland Map, owned by Yale University and valued at $20m, is in fact a 20th Century fake.

I can't see how it could have been done in the 15th century

Professor Robin Clark, University College London
Controversy has raged over the claim for the past 35 years.

And this week, experts from University College, London, UK, said that fresh analysis of the ink on the map added weight to this allegation.

Interestingly, their report was published at the same time as the details were released of a radiocarbon dating study of the parchment itself.

This shows that parchment at least is likely to be from the 15th Century, even if the actual map was drawn on much later.

Viking influence

The Vinland Map appears to show - to a high level of accuracy - not only the main countries of western, northern and Mediterranean Europe, but also Greenland and Iceland.

But what really caused a stir when the map was unveiled in 1965 was the inclusion of "Vinland", a small area to the west of Greenland perhaps depicting a section of the east coast of Canada or the US.

If the map were genuine, it would pre-date the feted voyage of Christopher Columbus by some years - and would possibly have relied instead on the experiences of Viking explorers who almost certainly reached North America in the 10th Century.

This would make the Vinland Map the earliest cartographic representation of North America. But is it real?

Laser scattering

The University College London study, led by Professor Robin Clark, and published in the journal Analytical Chemistry, used a technique involving laser light to examine the lines drawn on to the parchment.

The light is scattered in different wavelengths dependent on the chemical composition of the ink, so the compounds involved can be identified.

The Vinland Map is curious in that there is a yellowish line directly underneath a black line on top.

Professor Clark's study found traces of a chemical called anatase - a form of titanium dioxide - in the yellow lines at several points on the map.

This pigment was not synthesized as part of inks until at least the 1920s - strongly suggesting that the map is a modern fake.

The London team found no anatase anywhere else on the map, pointing to it being a constituent of the yellow line rather than a product of later contamination.

Yellow key

The reason for the presence of the yellow line is key to the authenticity of the map.

Medieval iron-based inks tend to erode over time, leaving a yellow or brown stain.

The London team also proved that the black inks used on the map were not iron-based.

Some have speculated that a forger may have included the yellow line to make it look like this kind of deterioration was occurring.

Professor Clark told BBC News Online that while he can only guess at the precise provenance of the map, his work means it is highly unlikely to be prior to the 1920s.

'Good fake'

He said: "I can't see how it could have been done in the 15th Century.

"I don't know how it was made, but I can't think of any other explanation."

Some scientists suggest that the titanium dioxide could be the product of long-term deterioration of ancient inks, but Professor Clark remains unconvinced.

"We have not seen this titanium dioxide on any other ancient manuscripts, and we have used this microscopy to look at thousands.

"But if it does prove to be a forgery, it's a very good one."

Carbon clue

The radiocarbon dating study, published in the journal Radiocarbon, pinpoints the manufacture of the parchment on which the map is drawn to approximately AD 1434.

This is 60 years before the Columbus expedition.

It means that the parchment could conceivably have been produced to coincide with the Catholic Council of Basel, convened a half-century before the Columbus voyage.

Dr Garman Harbottle, who carried out the study, said: "While the date result itself cannot prove that the map is authentic, it is an important piece of new evidence that must be considered by those who argue that the map is a forgery and without cartographic merit."

See also:

03 Dec 01 | England
15 Jul 00 | Europe
05 Apr 00 | Science/Nature
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