Letterpress Printing

one of the principal methods of printing multiple copies of texts and drawings. In this method the printing surface and blank areas are set at different levels (not on the same plane); the elements to be printed are higher, and the blank areas lower. This makes it possible during the rolling of the rubber inking cylinders to place the ink selectively, only on the printing elements, and to transfer the ink from them to the surface to be printed. Owing to the relative simplicity and speed in making up plates (especially those for reproducing texts), the high quality of the product, and high productivity, letterpress printing is used extensively for printing newspapers, magazines, books, and multicolored illustrations. Printing done by letterpress is marked by the precision and sharpness of the elements of the image, high ink saturation, and a slight relief on the reverse side of the sheet.

The methods of letterpress printing have been in use for more than 1,000 years. The first plates were flat wooden boards with an even, smooth surface on which the image to be printed was created by incising (hollowing out) the areas that were not meant to be printed. Such plates are sometimes used even today for artistic reproduction (xylography and engraving). The invention of book printing and the extensive development of letterpress printing were linked, first, with the creation of composite plates, made up of separately cast or cut letters and signs.

Today text plates for letterpress printing are made up by hand from separate, previously cast letters and signs or are made up on typesetting machines (monotype and linotype) or phototypesetting machines. Various illustrations in letter-press are printed from stereotype blocks made by etching (zincography) or engraving. A distinction is made between primary and secondary plates. The primary or original plates for letterpress printing are flat plates, including typeset and stereotype blocks, from which printing is done directly. So-called flexible plates, on which the relief image is made by etching out the blank spaces on a metallic plate or by “washing out” on a photopolymer layer applied to a backing sheet, also belong to this category. The secondary plates, or stereotypes, are made from the primary plates, usually in order to make multiple copies or to make curved plates for printing on a rotary press. Modern secondary plates are cast metallic plates, pressed plastic or rubber plates, or electro-stereotype plates. Printing from flat letterpress plates is done on crucible or so-called flat-bed printing machines; from curved plates, on sheet or roller rotary presses. There is also the offset method of printing, in which the image is first transferred from the plate to a rubber base (a cylinder coated with rubber), and then to the paper. Modern letterpress rotary presses can print multicolored newspapers, magazines, and books on a continuous paper web as wide as 2 m at a speed ranging from 3 to 15 m/sec.