NEW HAVEN, Conn. — Two new studies add fresh fuel to a decades-old debate about whether a parchment map of the Vikings’ travels to the New World, purportedly drawn by a 15th century scribe, is authentic or a clever 20th century forgery.
Using carbon dating, scholars from the Smithsonian Institution, the University of Arizona and Brookhaven National Laboratory determined the map predates Christopher Columbus by about 50 years, proving he was not the first European to reach America.
But researchers at University College in London, who analyzed the map’s ink under a Raman microscope, concluded that the map was produced after 1923.
Both studies were published independently in scholarly journals, the researchers announced Monday.
“The results demonstrate the great importance of modern analytical techniques in the study of items in our cultural heritage,” said Robin J.H. Clark, a University College professor.
The research by Clark and a colleague, Katherine Brown, is included in the July 31 issue of Analytical Chemistry, the journal of the American Chemical Society.
The Smithsonian Institution study, published in the July issue of the journal Radiocarbon, concludes that the map’s parchment was produced around 1434 — exactly the right time for the map to be authentic.
“It’s not a trivial thing for a forger to get a parchment” from that time period,” said Jacqueline Olin, a research chemist recently retired from the Smithsonian.
The authenticity of the map — valued at more than $20 million — has been debated since the 1960s, when benefactor Paul Mellon donated it to Yale.
The map depicts the world, including the north Atlantic coast of North America. It includes text in medieval Latin and a legend that describes how a Norseman, Leif Eriksson (spelled Eiriksson on the document), found the new land called Vinland around the year 1000.
The map was included in a medieval travelogue book and sold in the 1950s to a Connecticut dealer, then to Mellon. The original dealer died without revealing his source.
Yale has not taken a position on whether the map is authentic.
In the 1970s, the university hired the late Chicago chemist Walter McCrone Jr. to do a microscopic analysis. He focused on the map’s ink — a black layer that is flaking off over a yellowish layer that adheres firmly to the parchment.
McCrone found round, uniform crystals of anatase in ink. Anatase, a form of titanium dioxide, has been used to produce inks since the 1920s.
Anatase is found in nature, but in small amounts that would be found in jagged, irregular crystals if a medieval scribe had used it to make the Vinland Map’s inks, he said. Based on this conclusion, McCrone pronounced the map a fake.
However, McCrone’s conclusions were debunked in a 1995 book by Thomas Cahill, a professor of atmospheric science and physics at the University of California at Davis, and one of Cahill’s colleagues.
Among other findings, the researchers concluded that most of the crystals McCrone found were not anatase, and that a third of the ink contained no titanium.
Clark’s study, using a Raman microscope, found that anatase was detected solely in the yellowish ink lines, and not elsewhere on the parchment. The Raman microscope uses a laser beam that scatters off molecules as radiation with different colors.
Yellow lines are sometimes left behind when medieval ink, made of iron gallotannate, degrades. Clark said a forger would know about the yellow residue and would try to reproduce it.
But, the black ink on top of the yellow ink was found to be carbon-based, not iron gallotannate, so no yellow residue should be present, Clark said.
Not so, say Olin and other researchers who used a thin strip of parchment taken from the map to date it with a mass spectrometer. Their results showed the map dates to 1434.
“The question of whether the parchment came from the period is settled,” Olin said.