Before beginning work on the Bible around 1450, Gutenberg experimented with printing single sheets of paper and even small books, including a simple Latin grammar textbook. To this end, he created a printing press and developed a method of casting individual pieces of metal type.
Gutenberg's press was made of wood and might have been modeled on winepresses of his time. His type was made of a metal alloy that would melt at a low temperature but was strong enough to withstand being squeezed in a press. It was long thought that Gutenberg had originated the punch-matrix-mold system of typecasting used for centuries by subsequent typemakers, as demonstrated in the video on this page. Recent research, however, indicates that he may have used a cruder sand-casting system in which the character is carved into the sand and the metal alloy is poured into this mold to create the type piece. This process would have been a long and laborious one because nearly 300 different pieces of type are used in the Bible, each one requiring its own sand-cast mold.
The exact number of presses in Gutenberg's shop is unknown, but his large production indicates that more than one press was used. A skilled typesetter selected the individual characters of type for each line of the text and set them backwards in a frame, from right to left, so that the text would read correctly when printed. The frame was then placed on the bed of the press, where ink was applied to the type. The sheet of paper was slightly moistened before being placed over the type and frame, and then a stout pull by the pressman pushed the paper down onto the ink and type, completing the printing process.
No one knows exactly how many copies of the Bible were printed, but it is estimated that between 160 and 180 copies were produced. Most were printed on paper and the rest on vellum or scraped calfskin, a more expensive material. Although the original cost of the book is not known, most copies were likely purchased by wealthy churches and monasteries.