The report will appear in the Dec. 1 edition of Analytical Chemistry, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
The Vinland Map is a drawing of Iceland, Greenland and the northeastern seaboard of North America that has been dated to the mid-15th century, suggesting that Norse explorers charted North America long before Columbus. The map, which has had a contentious history since its discovery in the 1950s, resides at the Beinecke Rare Book and Manuscript Library of Yale University. It has been valued at more than $20 million.
"Many scholars have agreed that if the Vinland Map is authentic, it is the only existing cartographic representation of North America prior to Columbus," says Jacqueline Olin, a member of the advisory committee of the Smithsonian Center for Materials Research and Education in Washington, D.C. "Its date is important in establishing the history of European knowledge of the lands bordering the western North Atlantic, and the deeper question of Columbus's own possible awareness."
In July 2002, two papers about the Vinland Map were published simultaneously in separate scientific journals — one in Radiocarbon, which set a date for the map's parchment at about 1434 using carbon dating; and another in Analytical Chemistry, claiming that the map is really just a clever 20th-century forgery on medieval parchment.
Olin, who was involved in the Radiocarbon research, wrote the new Analytical Chemistry paper in response to the controversy sparked by last year's dueling papers.
Since the age of the parchment is not in dispute, Olin says, "The information needed to prove that the Vinland Map is medieval rests with the ink used to draw it."
Before the development of the printing press, manuscripts were written in either carbon-based inks or iron gallotannate inks. Erosion of the latter often leads to yellow staining - a feature exhibited by the Vinland Map.
In last year's Analytical Chemistry paper, British researchers analyzed the ink with Raman microprobe spectroscopy and claimed that it is made up of two parts: a yellowish line that adheres strongly to the parchment overlaid with a black line that appears to have flaked off.
Because they found the black line contained carbon, the researchers assumed the ink was not iron gallotannate, meaning there should be no yellow staining. They proposed that the yellow line was put there by a clever forger who knew it was a common feature of medieval manuscripts. This line contained anatase, a precipitated form of titanium dioxide. Since anatase was not synthesized until 1917, they considered this as evidence that the Vinland Map is a forgery.
To the contrary, the ink may help prove the map's authenticity, says Olin. "The presence of carbon in an ink is not evidence that the ink is a carbon ink," she says. "It could just as well have been iron gall ink to which carbon has been added as a colorant." Carbon was added to medieval iron gall inks to enable scribes to view their writing while the transparent ink mixture was reacting to form its black color.
"The source of the iron in medieval inks is green vitriol, an iron sulfate," Olin continues. "Green vitriol would include anatase if the iron source from which it was made included the iron-titanium mineral ilmenite."
Researchers have reported the absence of ilmenite in the ink of the Vinland Map, but that would only mean it was not present in the sulfate used to make the ink, Olin says. In earlier work, she made a simulated 15th century ink using ilmenite for the preparation of green vitriol. The resulting ink contained anatase, and no ilmenite.
There has also been no discussion about the significance of the other elements found in the ink, Olin says. She used archaeological reports to show that the presence of copper, aluminum and zinc — all found in the Vinland Map's ink — would be consistent with medieval production methods from green vitriol. Additionally, these elements raise serious doubts about the possibility of forgery, because 20th century iron gall inks would not be produced using medieval hydrometallurgy, which is responsible for the presence of these elements. No forger in the first half of the 20th century could be expected to know about these extra components, according to Olin.
— Jason Gorss
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