YALE UNIVERSITY PRESS

To some, the Vinland map offers proof that Norse explorers discovered North America before Columbus did; to others, it is simply a well-crafted forgery. Last year the publication of two studies that supported opposite conclusions fueled debate over the map's origins. One research group determined that the parchment indeed dates back to 1434, but a second group countered that the map's ink was distinctly modern. In the December 1 issue of the journal Analytical Chemistry, Smithsonian Institution scientist Jacqueline S. Olin, who worked with the group that dated the map's paper, suggests an alternative to the ink explanation.

The forgery accusations resulted from the presence of anatase, a rare form of titanium dioxide that could not be synthesized until the 1920s, in the ink lines on the Vinland map. In addition, the drawing contains both a yellow component that adheres strongly to the parchment and an overlaid black line, which is a telltale sign of iron gallotannate inks used during medieval times. But the 2002 study also detected the presence of carbon, a constituent of medieval inks that do not leave the same type of yellow stains. The group thus argued that a forger laid the different colors on the parchment separately to create the appearance of antiquity. In the new work, Olin proposes that the presence of carbon does not necessarily mean that the ink was not an iron gallotannate ink: "It could just as well have been iron gall ink to which carbon has been added as a colorant," she notes.

Olin also proposes a mechanism to explain the presence of anatase. Medieval inks containing iron were synthesized from a type of iron sulfate known as green vitriol. If the green vitriol, in turn, had come from an iron source that contained the mineral ilmenite (an iron-titanium mix), the resulting ink would include anatase, Olin explains. Although other researchers have reported that the Vinland map does not contain ilmenite, Olin notes that she made a 15th-century ink using ilemite to make green vitriol and then an iron gallotannate ink. The final product contained anatase but no ilmenite.

Other elements that are present in the Vinland ink and are indicative of 15th-century production processes include copper, aluminum, zinc and gold. "The elemental composition of the ink is consistent with a medieval ink," Olin writes. Despite this latest study, the Vinland map's ancestry will no doubt continue to be a source of discord: "It is sometimes possible on the basis of analytical studies to prove that an object is a forgery," Olin concludes. "It is very difficult to prove that an object is authentic."