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Misplaced Holes. From the first glance, it was the map that excited Marston and Victor. It contained the usual overscaled version of Europe.
India (TERRA INDICA) is slewed around due east of the Mediterranean, with a diminished Asia and China to the north of it. Offshore, across the Magnum mare Tartarorum, are renderings of large offshore islands, probably based on reports of Japan. Africa is lopped off below Ethiopi, but shows the magnus [ft] uuius which is apparently the Niger. In the Atlantic, there are the two mythical quad-shaped islands beyond the Azores that most medieval cartographers insistently put in. But in the upper left-hand corner were the unmistakable outlines of Greenland and Vinland, the latter rounded off into an island in accordance with the medieval assumption that the universal sea surrounded any area that had not been explored. Both were plainly labeled (GRONELĀDA and VINLANDA INSULA).
While the map and text appeared to be genuine and written by the same hand, there were a couple of things that bothered the Yale scholars. Though both the map and text were slightly wormed, the wormholes on the two parts did not coincide. They were even more disturbed by a notation on the map which suggested that it was only part of a larger volume. Until these puzzling features were resolved, the map would always be somewhat suspect.
Several months later, Marston ordered two manuscripts from a London dealer, one of which was a modestly priced portion of the Speculum Historiale (Mirror of History) compiled by Vincent of Beauvais, the famed encyclopedist of the Middle Ages. When the Speculum manuscript arrived, it was in such an attractive 15th century binding that Dealer Witten asked to examine it. That night Witten telephoned Marston in great excitement. The Speculum manuscript was the key to the puzzle of the Vinland map and the text of the Carpini mission, which was later to be called "the Tartar Relation." The manuscript was written in the same hand, the watermarks on the paper were identical, and the wormholes showed that the map had been at the front of the volume and the Tartar Relation at the back.
The Dating. The chances against anyone having such a stroke of luck were astronomical, and that as much as anything was one of the reasons that Victor and Marston consulted R. A. Skelton and George D. Painter, two experts with the British Museum, for exhaustive research, evaluation and testing of the manuscript. In lengthy papers, crammed with scholarship and bristling with footnotes, Skelton and Painter tell in The Vinland Map and the Tartar Relation how they authenticated and dated both the map and the manuscript.
In brief, the dating rests on two major pieces of physical evidence. First, the scribe who drew the map and copied the text used a writing style known as Oberrheinische Bastarda, or Upper Rhineland bastard (or cursive) book hand, which is confined to the period 1415-1460. Since the handwriting is in fully developed form and free of accretions from styles that developed later, a date in the 1440s seems most likely. Second, the parchment and paper used can be traced to the same period, and a unique spectacled head of a bull used as a watermark on the paper shows it most likely was produced at a mill that began operating in Basel, Switzerland, about 1433.