Gutenberg returned to his hometown of Mainz after his time in Strasbourg. This marked a new phase in his life, as he began to focus more intently on developing his printing technology.

Gutenberg entered into a partnership with Johannes Fust, a wealthy Mainz merchant and lawyer, who provided him with a loan of 800 guilders to continue his printing experiments. This financial support was crucial in allowing Gutenberg to refine his press and movable type.

Fust provided Gutenberg with an additional loan of 800 guilders, indicating the ongoing expenses and commitment required to perfect the printing process. This loan was secured with the printing equipment as collateral.

The Gutenberg Bible, also known as the 42-line Bible (B42), was completed around 1455. It is considered the first major book printed using movable type in Europe and a landmark achievement in the history of printing. Only a limited number of copies were produced, making it incredibly rare and valuable.