The forerunners of today's modern printing presses were developed in Germany in the 15th century. They made use of the new concept of movable type, an invention generally credited to Johannes Gutenberg. Before Gutenberg's time, most books were copied by hand or printed from carved wooden blocks. Movable type used separate pieces of metal that could be easily set in place, locked into a form for printing, and then used again for another job.
The first presses consisted of two flat surfaces. Once set in place, the type was inked with a roller, and a sheet of paper was pressed against the type with a lever. Two people working together could print about 300 pages a day.
In the early 19th century, Friedrich Konig, another German, developed the first cylinder press. With a cylinder press, the paper is mounted on a large cylinder that is rolled over a flat printing surface.
The first rotary press was developed in the United States in 1865 by William Bullock. On this kind of press, the inked surface is on a revolving cylinder called a plate cylinder. The plate cylinder acts like a roller and prints onto a continuous sheet of paper (called a web) coming off a giant roll.
The speed and economy of the web press was improved by the discovery of offset printing in the early 20th century. In this process, the raised metal type used in earlier processes was substituted with a flexible plate that could be easily attached to the plate cylinder. The ink is transferred from the plate onto a rubber cylinder (called a blanket), then onto the paper. The printing plate never touches the paper but is "offset" by the rubber blanket.
Offset printing uses the process of lithography, in which the plate is chemically treated so that ink sticks only to the parts that are to be printed and is repelled by the non-print areas.
Offset lithography is the most common form of printing today and is used on both web-fed and sheet-fed presses. Web-fed presses are used for newspapers and other large-volume, lower-cost runs. The fastest web presses today can print about 150,000 complete newspapers in an hour. Sheet-fed presses, which print on single sheets of paper rather than a continuous roll, are used for smaller, higher-quality jobs.
Other forms of printing are gravure (in which depressions on an etched plate are inked and pressed to paper), flexography (a form of rotary printing using flexible rubber plates with raised image areas and fast-drying inks), screenprinting (which is used to print design on clothing, hats, and other fabric items), and letterpress (the most traditional method, in which a plate with raised, inked images is pressed against paper). Digital printing, also known as variable data printing, is the newest development in printing. In digital printing, no plates are used to print jobs. Ink is applied directly to the printing surface (such as paper).
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