The Vinland map is purportedly a 15th-century mappa mundi, redrawn from a 13th-century original. In addition to showing Africa, Asia and Europe, the map depicts a large island west of Greenland in the Atlantic labelled as Vinland; the map describes this region as having been visited in the 11th century. If authentic, such evidence is an important addition to archaeological findings such as the L'Anse aux Meadows Norse site in Newfoundland, documenting pre-Columbian Norse travels to the Americas, but the map has been controversial since it was first revealed in 1965, and both the most recent chemical analysis and the most recent scholarly monograph on the subject have suggested that it is a forgery.
The Vinland Map was bound together with a codex, Hystoria Tartarorum ("Description of the Tartars," sometimes referred to as the Tartar Relation). The Historia is a manuscript of undoubted authenticity that was at some point bound with the Vinland Map. It is a description of the history and manners of the Mongols that appears to be an early version of the memoir of Giovanni da Pian del Carpine, an Italian Franciscan friar who in 1245 made a trip to the supreme Khan at Karakorum. Carpine went on to write a more robust account of his travels, but the shorter "Tartar Relation" survived until the 15th century by being included as an addendum to a volume of Vincent of Beauvais's encyclopedic "Historical Mirror" (Speculum historiale). Before the items were first offered to Yale, probably while they were being rebound into two volumes, all traces of former ownership marks, except for a small part of a bright pink stamp which overlapped the writing on folio 223 of the Speculum, were removed, perhaps to avoid tax liability for the former owner.
In 1991, McCrone visited Yale to take new microsamples from the map, partly to check his earlier results, and partly to apply new techniques. Photomicrographs taken at 1 micrometer intervals through the thickness of ink samples demonstrated that the manufactured anatase particles were not just sticking to the surface, and Fourier transform spectroscopy identified the ink's binder as gelatin, probably made from animal skin. In July 2002, the authenticity of the map was again challenged. Using Raman spectroscopy, the presence of significant quantities of anatase was confirmed, and the remaining traces of black pigment in the ink were found to consist mostly of carbon, which should not have generated the yellowish residue (superficially characteristic of the decay of an iron-based ink) which is all that now survives over most of the length of the map's lines.
All of the other pages of the Hystoria Tartarorum and Speculum historiale were written using standard medieval iron gall ink. Nevertheless, chemist Jacqueline Olin, a retired researcher with the Smithsonian Institution, has conducted experiments which suggest a chain of circumstances that could conceivably have led to the production of the map ink in medieval times (though she herself did not produce finished ink, and others have pointed out possible reasons why).
Finally, there are a number of questions about the actual content of the map. The original authentication team recognized that it bore strong resemblances to a map made in the 1430s by Italian mariner Andrea Bianco – even to the extent of cutting off Africa where Bianco's map has a page fold – but with changes of shape, and major revisions in the far east and west. The most surprising revision is that the map depicts Greenland as an island, remarkably close to the correct shape and orientation (while Norway, of which Greenland was just a colony, is wildly inaccurate) although contemporary Scandinavian accounts—including the work of Claudius Clavus in the 1420s—depict Greenland as a peninsula joined to northern Russia. For practical purposes, the polar ice cap made this description true, and Greenland is not known to have been successfully circumnavigated until the 20th century. Skelton wondered also whether the revisions in the far east were meant to represent Japan, which would be another remarkable achievement for 15th-century cartography.
In addition, the text uses a Latin form of Leifr Eiriksson's name ("Erissonius") more consistent with 17th-century norms and with transmission through a French or Italian source. The Latin captions include several usages of the ligature æ; this was almost unknown in later medieval times (a simple e was written instead), and although the ligature was revived by Italian humanist scholars in the early 1400s, it is found only in documents of deliberately classicising style produced by Italian scribes, and never in conjunction with a Gothic style of script such as is seen in the Map.
Another point calling the map's authenticity into question was raised at the 1966 Vinland Map Conference: that one caption referred to Bishop Eirik of Greenland "and neighboring regions" (in Latin, "regionumque finitimarum"), a title known previously from the work of religious scholar Luka Jelic (1863–1922). An essay by British researcher Peter Foote for the Saga Book of the Viking Society (vol. 11, part 1), published shortly after the conference, noted that German researcher Richard Hennig had spent years, before the Vinland Map was revealed, fruitlessly trying to track Jelic's phrase down in medieval texts. It seemed that either Jelic had seen the Vinland Map and promised not to reveal its existence (keeping the promise so rigidly that he never mentioned any of the other new historical information on the map), or that he had invented the phrase as a scholarly description, and the Vinland Map creator copied him. In practice, because Jelic's work had gone through three editions, Foote was able to demonstrate how the first edition (in French) had adopted the concept from the work of earlier researchers, listed by Jelic, then the later editions had adapted the French scholarly phrase "évèque régionnaire des contrées américaines" into Latin.
One feature of the Vinland Map which is mentioned in passing by most investigators is the fold down the middle. Looking at the map, it is clear that the artist knew exactly where the fold was going to be, because several place-names start or finish right next to it while none are written straight across it, and the rivers of eastern Europe run parallel to it. On high-resolution images of the map, it is also clear that "fold" is not the right word. The two halves are held together only by the backing strip which binds the map into the "Tartar Relation" volume and allows it to be opened out flat. The British Museum scientists in 1967 found only one tiny sliver of parchment which might join the two halves, but Danish conservation experts in 2005 confirmed that they are separate. Kirsten Seaver has suggested, based on British Museum suggestions, that the two halves may never have been together – a forger could have found two separate blank leaves in the original "Speculum Historiale" volume, and joined them together with the binding strip. In this scenario, the mysterious chemical treatment of the parchment is intended to disguise slight differences of color and texture between the two halves, and the notch cut out of the bottom disguises a slight size difference (see bottom illustration).
The split has provided one potential benefit for scientific examination of the map: large numbers of tiny particles are trapped in it. In their essay for the revised Skelton book, the Cahill team argued that if one of these particles was accidentally selected by the McCrone team, it could produce some very surprising and misleading results, and they stated that to avoid such problems they themselves "did not analyze the particles compositionally at the time". In fact, the Cahill team had analyzed some of the particles shortly after their main tests, and had found the explanation of the most surprising single result in McCrone's work. In addition to pale-colored particles containing anatase, they found in the fold many other particles, chemically distinct from those on the map. The McCrone team had found one of these anomalous particles, containing a significant percentage of chromium, sticking loosely to the surface of the ink line, and, by accident, featured it prominently in their second published report (1988) without explaining that it was probably contamination. The Cahill team, keeping their own analysis pretty much to themselves until 2000, never speculated publicly on the sources of the loose particles.