Printing Technology
Letterpress Printing
Letterpress printing is a term for printing text with movable type, in which the raised surface of the type is inked and then pressed against a smooth substance to obtain an image in reverse. In addition to the direct impression of inked movable type onto paper or another receptive surface, the term letterpress can also refer to the direct impression of inked media such as zinc "cuts" (plates) or linoleum blocks onto a receptive surface.
History
Early Chinese woodblock printing used characters or images carved in relief from before 750AD, and this form of printing was widespread throughout Eurasia as a means of printing patterns on textiles. Printing of images, first on cloth, then from about 1400 on paper was practised in Europe. In the 1400s, Johann Gutenberg (among others) is credited with the invention of movable type printing from individually-cast, reusable letters set together in a forme (frame). This had previously been invented in Asia, but the two inventions were probably not connected. He also invented a wooden printing-press where the type surface was inked and paper laid carefully on top by hand, then slid under a padded surface and pressure applied from above by a large threaded screw. Later metal presses used a knuckle and lever arrangement instead of the screw, but the principle was the same.
With the advent of industrial mechanisation, the inking was carried out by rollers which would pass over the face of the type and move out of the way onto a separate ink-bed where they would pick up a fresh film of ink for the following sheet. Meanwhile a sheet of paper was slid against a hinged platen (see image) which was then rapidly pressed onto the type and swung back again to have the sheet removed and the next sheet inserted (during which operation the now freshly-inked rollers would run over the type again). In a fully-automated 20th century press, the paper was fed and removed by vacuum sucker grips.
Industrial-scale use in the 20th century
Rotary presses were used for high-speed work. In the oscillating press, the forme slid under a drum around which each sheet of paper got wrapped for the impression, sliding back under the inking rollers while the paper was removed and a new sheet inserted. In a newspaper press, a papier-mâché mixture (flong) was used to make a mould of the entire forme of type, then dried and bent, and a curved metal plate cast against it. The plates were clipped to a rotating drum, and could thus print against a continuous reel of paper at the enormously high speeds required for overnight newspaper production.
exmample of how a letterpress works