Johannes Gutenberg did not invent printing, paper or even movable type. What he did, in the German city of Mainz in the mid fifteenth century, was combine several technologies into a system that could produce books quickly, cheaply and accurately. The system worked so well that its basic method lasted, with improvements, for about 350 years.

Who was Gutenberg?

Much of Gutenberg's life is known only from legal and financial records. He was born in Mainz around 1400, into a family of the city's patrician class, and seems to have trained in metalwork, perhaps as a goldsmith. In the 1430s he lived in Strasbourg, where records of a lawsuit from 1439 show him in a partnership making metal mirrors for pilgrims and working on a secret process that may have been an early form of printing. By about 1448 he was back in Mainz, borrowing money to set up a workshop.

The four parts of the system

• Type made by a hand mould. Gutenberg's key invention was probably an adjustable hand mould for casting type. A craftsman cut each letter in reverse on the end of a hard steel punch, then struck it into softer copper to make a matrix. Placed in the mould, the matrix allowed molten metal to be poured in, producing a piece of type. The mould could be adjusted for letters of different widths, such as a narrow “i” and a wide “m.” In this way thousands of identical letters could be cast quickly.
• A metal alloy. The type was made from an alloy based mainly on lead, tin and antimony. It melted easily, filled the mould sharply, cooled fast and was hard enough to survive repeated printing.
• Oil-based ink. Water-based inks used for woodblocks did not stick well to metal type. Gutenberg used an oil-based ink, closer to a varnish, which clung to the type and printed a dense, dark impression.
• The press. He adapted the screw press, already used for squeezing grapes and olives and for pressing paper, to press the paper evenly onto the inked type.

Type was stored in cases with compartments for each letter. A compositor picked letters one by one into a handheld tray, line by line, then locked the lines into a frame to form a page. After printing, the type was cleaned and returned to the cases for reuse.

The Gutenberg Bible

Gutenberg's most famous product is the Latin Bible known as the Gutenberg Bible, or the 42-line Bible, after the number of lines in most of its columns. It was completed around 1454 to 1455. In March 1455 the future Pope Pius II wrote in a letter that he had seen sections of it at a fair in Frankfurt and that its script was so clean and correct one could read it without glasses. Scholars estimate that about 180 copies were printed, some on paper and some on vellum. Around fifty survive, in whole or in large part, and they are among the most valuable books in the world.

The Bible was designed to look like a fine manuscript. Its typeface imitated the formal script of German scribes, and spaces were left for colored initials and decoration to be added by hand, so that each surviving copy looks slightly different.

Debt and lawsuit

Printing required large investment: metal, paper, presses, skilled workers and years of work before any income. Gutenberg borrowed heavily from a Mainz businessman, Johann Fust. In 1455 Fust sued for repayment, and the court's decision appears to have cost Gutenberg control of much of his workshop. Fust and Gutenberg's skilled assistant Peter Schöffer continued printing. In 1457 they produced the Mainz Psalter, the first printed book to name its printers and give a date. Gutenberg seems to have continued printing on a smaller scale. In 1465 the archbishop of Mainz gave him a court pension, and he died in 1468, not rich, and hardly known outside his city.

Printing for money

Not everything Gutenberg printed was grand. Among the earliest dated items from Mainz are indulgences, printed forms sold by the church that promised the reduction of punishment for sins, with blanks for the buyer's name. These short jobs earned quick money. It is an irony of history that printing would later spread the attacks on indulgences that helped split the Western church.

Worked example: setting one page

Follow a compositor in Mainz around 1455 as he prepares one page of the Bible.

1. Read the copy. He works from a manuscript or marked text beside him.
2. Pick the letters. Reading a word, he takes each letter from its compartment and places it upside down and in reverse order in his tray, adding spacers between words.
3. Justify the line. To make every line end evenly at the margin, he adjusts spacing and uses abbreviations and alternative letter forms, of which the Bible's type included many.
4. Lock up the page. When the column is complete, it is tied, placed with others in a frame and tightened.
5. Proof and correct. A test sheet is printed and checked. Errors are fixed by swapping individual letters.
6. Print. The pressmen ink the type, lay damp paper on it and pull the press, producing one sheet after another.

Setting a page might take a skilled compositor most of a day. But once it was set, the press could print hundreds of identical copies. That trade, heavy work up front and cheap copies afterward, is the economic logic of print, and of every mass medium that followed, from newspapers to software.