Katherine L. Brown and Robin J. H. Clark of University College London used a technique known as Raman microphone spectroscopy to examine the ink on the map. The drawing contains both yellowish lines that adhere strongly to the parchment and overlaid black lines that have begun to flake off. The researchers detected anatase, a rare form of titanium dioxide, solely in the yellow lines. Because anatase could not be synthesized until the 1920s, detection of the compound has sparked forgery accusations in the past. Brown and Clark also found that the black ink contains carbon, which would not produce the telltale yellow lines that mark medieval inks made of iron gallotannate. As a result, the scientists suggest that a forger actually applied the two components separately on the parchment to give the appearance of antiquity. According to Clark, "the Raman results provide the first definitive proof that the map itself was drawn after 1923."
Analysis of the parchment, however, conducted by Douglas J. Donahue of the University of Arizona, Jacqueline Olin of the Smithsonian Center for Materials Research and Education and Garman Harbottle of Brookhaven National Laboratory led to a different conclusion. In 1995, Yale University, which owns the map, permitted the team to cut a three-inch-long strip off the lower right-hand corner of the map. Using carbon-dating techniques, which measure the relative amounts of different isotopes of carbon, the researchers determined that the parchment dates to between AD 1411 and AD 1468. "While the date itself cannot prove that the map is authentic," Olin notes, "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." Carbon testing of the ink itself was not possible because the required amount of sample was prohibitively large.
If the map is indeed genuine, its value is estimated to be almost $20 million. Whatever its origin, it is an impressive piece of handiwork. "If it is, in fact, a forgery," Harbottle says, "then the forger was surely one of the most skillful criminals ever to pursue that line of work."