In November 2002 physicist and software developer Blaise Agüera y Arcas and Paul Needham, Librarian of the Scheide Library at Princeton University, working on original editions in the Scheide Library, used high resolution scans of individual characters printed by Gutenberg, and image processing algorithms, to locate and compare variants of the same characters printed by Gutenberg. As a result of this research it appears that the method of producing movable type attributed to Gutenberg developed in phases rather than as a complete system.
"The irregularities in Gutenberg's type, particularly in simple characters such as the hyphen, made it clear that the variations could not have come from either ink smear or from wear and damage on the pieces of metal on the types themselves. While some identical types are clearly used on other pages, other variations, subjected to detailed image analysis, made for only one conclusion: that they could not have been produced from the same matrix. Transmitted light pictures of the page also revealed substructures in the type that could not arise from punchcutting techniques. They [Agüera y Arcas and Needham] hypothesized that the method involved impressing simple shapes to create alphabets in "cuneiform" style in a mould like sand. Casting the type would destroy the mould, and the alphabet would need to be recreated to make additional type. This would explain the non-identical type, as well as the substructures observed in the printed type. Thus, they feel that "the decisive factor for the birth of typography", the use of reusable moulds for casting type, might have been a more progressive process than was previously thought. . . . " (Summary from the Wikipedia article on Johannes Gutenberg, accessed 02-08-2209).
Blaise Agüera y Arcas and Paul Needham, "Computational analytical bibliography," Proceedings Bibliopolis Conference The future history of the book', The Hague: Koninklijke Bibliotheek, (November 2002).
Agüera y Arcas, "Temporary Matrices and Elemental Punches in Gutenberg's DK type", in: Jensen (ed) Incunabula and Their Readers. Printing , Selling, and Using Books in the Fifteenth Century (2003) 1-12.