linguistic:paraphrasing, structural:reformatting, information:classification
Printing method

Gutenberg's early printing process, and what texts he printed with movable type, are not known in great detail. His later Bibles were printed in such a way as to have required large quantities of type, some estimates suggesting as many as 100,000 individual sorts. Setting each page would take, perhaps, half a day, and considering all the work in loading the press, inking the type, pulling the impressions, hanging up the sheets, distributing the type etc., the Gutenberg–Fust shop may have employed many craftsmen.

Gutenberg's technique of making movable type remains unclear. In the following decades, punches and copper matrices became standardized in the rapidly disseminating printing presses across Europe. Whether Gutenberg used this sophisticated technique or a somewhat primitive version has been the subject of considerable debate.

In the standard process of making type, a hard metal punch (made by punchcutting, with the letter carved back to front) is hammered into a softer copper bar, creating a matrix. This is then placed into a hand-held mould and a piece of type, or "sort", is cast by filling the mould with molten type-metal; this cools almost at once, and the resulting piece of type can be removed from the mould. The matrix can be reused to create hundreds, or thousands, of identical sorts so that the same character appearing anywhere within the book will appear very uniform, giving rise, over time, to the development of distinct styles of typefaces or fonts. After casting, the sorts are arranged into type cases, and used to make up pages which are inked and printed, a procedure which can be repeated hundreds, or thousands, of times. The sorts can be reused in any combination, earning the process the name of "movable type".

The invention of the making of types with punch, matrix and mold has been widely attributed to Gutenberg. However, recent evidence suggests that Gutenberg's process was somewhat different. If he used the punch and matrix approach, all his letters should have been nearly identical, with some variation due to miscasting and inking. However, the type used in Gutenberg's earliest work shows other variations.

In 2001, the physicist Blaise Agüera y Arcas and Princeton librarian Paul Needham, used digital scans of a Papal bull in the Scheide Library, Princeton, to carefully compare the same letters (types) appearing in different parts of the printed text. Gutenberg's type had irregularities, particularly in simple characters like the hyphen. These variations could not have been caused by ink smears or wear on the metal pieces. Detailed image analysis suggests the variations could not have come from the same matrix. Examination of transmitted light pictures of the page revealed substructures, in the type, that could not have been made using traditional punchcutting techniques.

Based on these observations, researchers hypothesized that Gutenberg's method involved impressing simple shapes in a " cuneiform " style onto a matrix made of a soft material, such as sand. Casting the type would then destroy the mold, necessitating the recreation of the matrix for each additional sort. This hypothesis could potentially explain both the variations in the type and the substructures observed in the printed images.

Thus, they speculated that "the decisive factor for the birth of typography", the use of reusable moulds for casting type, was a more progressive process than was previously thought. They suggested that the additional step of using the punch to create a mould that could be reused many times was not taken until twenty years later, in the 1470s. Others have not accepted some or all of their suggestions, and have interpreted the evidence in other ways, and the truth of the matter remains uncertain.

A 1568 book Batavia by Hadrianus Junius from Holland claims the idea of the movable type came to Gutenberg from Laurens Janszoon Coster via Fust, who was apprenticed to Coster in the 1430s and may have brought some of his equipment from Haarlem to Mainz. While Coster appears to have experimented with moulds and castable metal type, there is no evidence that he had actually printed anything with this technology. He was an inventor and a goldsmith. However, there is one indirect supporter of the claim that Coster might be the inventor. The author of the Cologne Chronicle of 1499 quotes Ulrich Zell, the first printer of Cologne, that printing was performed in Mainz in 1450, but that some type of printing of lower quality had previously occurred in the Netherlands. However, the chronicle does not mention the name of Coster, while it actually credits Gutenberg as the "first inventor of printing" in the very same passage (fol. 312). The first securely dated book by Dutch printers is from 1471, and the Coster connection is today regarded as a mere legend.

The 19th-century printer and typefounder Fournier Le Jeune suggested that Gutenberg was not using type cast with a reusable matrix, but wooden types that were carved individually. A similar suggestion was made by Nash in 2004.