Johannes Gutenberg's work on the printing press began in approximately 1436 when he partnered with Andreas Dritzehn—a man who had previously instructed in gem-cutting—and Andreas Heilmann, owner of a paper mill. However, it was not until a 1439 lawsuit against Gutenberg that an official record existed; witnesses' testimony discussed Gutenberg's types, an inventory of metals (including lead), and his type molds. Having previously worked as a professional goldsmith, Gutenberg made skillful use of the knowledge of metals he had learned as a craftsman. He was the first to make type from an alloy of lead, tin, and antimony, which was critical for producing durable type that produced high-quality printed books and proved to be much better suited for printing than all other known materials. To create these lead types, Gutenberg used what is considered one of his most ingenious inventions, a special matrix enabling the quick and precise molding of new type blocks from a uniform template. His type case is estimated to have contained around 290 separate letter boxes, most of which were required for special characters, ligatures, punctuation marks, and so forth. Gutenberg is also credited with the introduction of an oil-based ink which was more durable than the previously used water-based inks. As printing material he used both paper and vellum (high-quality parchment). In the Gutenberg Bible, Gutenberg made a trial of coloured printing for a few of the page headings, present only in some copies. A later work, the Mainz Psalter of 1453, presumably designed by Gutenberg but published under the imprint of his successors Johann Fust and Peter Schöffer, had elaborate red and blue printed initials.