Gutenberg Bible
In 1952, Kraus purchased a copy of an extremely rare incunabula, the Constance Missal, then known in only two copies. Bearing no date, it was printed with type nearly identical to, but seemingly more primitive than, that used in the 1457 and 1459 Psalters, and some scholars believed that it might be the first printed book, pre-dating the Gutenberg Bible. Kraus sold it as a major bibliographical prize to the Morgan Library. Several years later, Allan Stevenson, by a brilliant and painstaking comparison of the different states of wear in the watermarks in the Constance Missal with those in dated books, conclusively established that it was printed in 1473, nearly 20 years after the Gutenberg Bible. Despite the definitive proof to the contrary, Kraus still professed that, "Speaking for myself, I believe that the Constance Missal is earlier than the Gutenberg Bible."