Johannes Gutenburg Begins Operation of First Mechanical Printing Press

Around 1439, Gutenberg was involved in a financial misadventure making polished metal mirrors (which were believed to capture holy light from religious relics) for sale to pilgrims to Aachen: in 1439 the city was planning to exhibit its collection of relics from Emperor Charlemagne but the event was delayed by one year and the capital already spent could not be repaid. When the question of satisfying the investors came up, Gutenberg is said to have promised to share a "secret". It has been widely speculated that this secret may have been the idea of printing with movable type.[6] Legend has it that the idea came to him "like a ray of light".

At least up to 1444, he lived in Strasbourg, most likely in the St. Arbogast suburb. It was in Strasbourg in 1440 that Gutenberg perfected and unveiled the secret of printing based on his research, mysteriously entitled Kunst und Aventur (art and enterprise). It is not clear what work he was engaged in, or whether some early trials with printing from movable type may have been conducted there. After this, there is a gap of four years in the record. In 1448, he was back in Mainz, where he took out a loan from his brother-in-law Arnold Gelthus, presumably for a printing press.

By 1450, the press was in operation, and a German poem had been printed, possibly the first item to be printed there. Gutenberg was able to convince the wealthy moneylender Johann Fust for a loan of 800 guilders. Peter Schöffer, who became Fust's son-in-law, also joined the enterprise. Schöffer had worked as a scribe in Paris and designed some of the first typefaces.

Gutenberg's workshop was set up at Hof Humbrecht, a property belonging to a distant relative. It is not clear when Gutenberg conceived the Bible project, but for this he borrowed another 800 guilders from Fust, and work commenced in 1452. At the same time, the press was also printing other, more lucrative texts (possibly Latin grammars). There is also some speculation that there may have been two presses, one for the pedestrian texts, and one for the Bible. One of the profit-making enterprises of the new press was the printing of thousands of indulgences for the church, documented from 1454–55.

In 1455 Gutenberg published his 42-line Bible, commonly known as the Gutenberg Bible. About 180 were printed, most on paper and some on vellum.