means of producing reproductions of written material or images in multiple copies. There are four traditional types of printing: relief printing (with which this article is mainly concerned), intaglio, lithography, and screen process printing. Relief printing encompasses type, stereotype, electrotype, and letterpress. Flexographic printing is a form of rotary letterpress printing using flexible rubber plates and rapid-drying inks.
For an account of type design, see type; typography. See also book; bookbinding.
The story of the invention of printing and of its early days is told in the article type. In the 15th cent. the art spread, directly and indirectly, from Mainz to many parts of Europe. It was brought to England in 1476 by William Caxton; to the New World in 1539 by Juan Pablos, who set up his press in Mexico City.
The first papermaking machine producing a continuous roll of paper and capable of delivering sheets in specific sizes—the Fourdrinier machine—was installed in London in 1803. Steam power was successfully applied to the printing press in 1810 by Friedrich Koenig, a German. The invention did not improve the quality of the product but greatly increased the output of the machine. In Koenig's press, the type bed remained flat as in hand presses, but the paper was pressed on the type by a cylinder. The Adams power press was invented by an American, Isaac Adams, in 1827.
In 1846 and 1847, Richard March Hoe designed a rotary press in which stereotype plates were for the first time arranged in a true cylinder. In 1866 a press known later as the Walter press was patented in England; in this press the printing surfaces were not types but stereotype plates curved to form parts of cylinders. The invention of ways of making paper in sheets of any desired length, so that paper could be fed to cylinder presses from rolls, assisted in increasing the speed of printing. Machines for folding newspapers were incorporated with the power cylinder press.
Not until the late 19th cent. were typesetting machines invented. The Linotype machine, invented by Ottmar Mergenthaler in Baltimore in 1884, produced a metal slug corresponding to a single line of type as set by hand in printing. It was first put into operation at the New York Tribune in 1886. Operated from a keyboard like that of a typewriter, the machine assembled brass matrices into a line, cast the line, and distributed the matrices. The Intertype machine was substantially similar to the Linotype machine, and the matrices made by either machine could be used in the other.
The third principal typesetting machine is the Monotype, patented by Tolbert Lanston in 1887 and first produced commercially in 1897. The Monotype makes each character separately, assembling the characters as in hand composition, for which the Monotype characters can be used. Before electronic composition, monotype had an advantage in setting certain kinds of copy, e.g., mathematical and scientific material, where special symbols or other problems may be involved.
In intaglio printing, such as the etching and the steel engraving, the design to be printed is lower than the surface of the plate, which is wiped clean before each impression, leaving the incised design filled with ink, which the paper receives. In gravure intaglio printing, tone is produced by varying the thickness of the ink of the printing surface through depressions of varying depth; minute points constitute the clean surface that keeps the paper from being pressed into the depressions. In photogravure the gravure plate is made by a photographic process. Rotogravure is photogravure adapted for printing by a rotary or cylinder press.
The third kind of printing, lithography, also known as planographic printing, was devised by Aloys Senefelder. Flat stones were the first lithographic plates and are still used, although a variety of thin metal, plastic, and paper plates are now also employed. A drawing is made on the plate with greasy ink or crayon, and water is then applied to the plate. When the plate is inked for printing, the greasy parts accept the ink and the wet parts do not. Preparing a printing surface so that ink will adhere only to parts of it is basic in all planographic printing.
Collotype, also called photogelatin, is a lithographic process that uses a gelatin-faced plate to achieve the tonal distribution obtained through screen dots in engraving. It is chiefly used in the reproduction of fine illustrations or of scientific subject matter requiring accuracy of detail.
Photolithography, offset, litho-offset, and offset lithography are synonyms in commercial printing for the most widely used form of planographic printing, based on a modification of the lithographic press featuring a rubber-covered cylinder between the printing cylinder and the impression cylinder. The plate cylinder transfers the image to the rubber blanket cylinder, which in turn offsets it on the paper carried by the impression cylinder. Offset and other forms of planographic printing, through many technical refinements, make possible increased production speeds, improved quality in the reproduction of fine tones, and a substantial reduction in the number of impressions required to reproduce full-color copy.
The fourth traditional type of printing, screen process, includes silk screen and has special applications in the printing industry. Silk screen printing is a form of stencil printing, i.e., printing where the ink is applied to the back of the image carrier and pushed through porous or open areas. The image is on a piece of silk stretched on a frame and backed by a rubber squeegee containing ink. The nonprinting areas on the silk screen are blocked out, and the ink is pushed through the porous areas corresponding to the design; the process is widely used for posters and for printing on glass, plastics, and textured surfaces. Mimeographing is another commercial application of stencil printing.
In three kinds of printing—relief, intaglio, and planographic—illustrations are often produced by the halftone process, in which a plate is made by photographing through glass marked with a network of fine lines (see also photoengraving). A usual form of color printing is by the Ben Day, or Benday, process, invented by New York printer Benjamin Day, which utilizes celluloid sheets to achieve proper shading and color. Printing in colors is sometimes done, as excellently in Japan, by applying inks of different colors by hand to the printing surface, but usually a separate printing surface is used for each ink.
In full-color printing four standard colors are used—yellow, cyan (a hue between blue and green), magenta, and black—the first three being the complementary colors of blue, red, and green. Other colors are produced by printing one color over another, as green by printing cyan on yellow. Black is used to print the text accompanying the illustration, and it is often used as a fourth color in the illustration itself to add strength and detail.
In recent years the use of photographic processes has expanded greatly, and the development of electronic devices, as well as other technological advances, has introduced a new era in the evolution of printing. The development of typewriters and personal computers capable of delivering justified and proportionally spaced copy has made possible the production of camera-ready books and has met the demands for several special types of printing.
Perhaps the most revolutionary innovation has been the introduction of photocomposition machines for setting type by photographic means. Two of these are analogous in principle to the Monotype and Intertype casting machines and have been produced by the respective companies under the trademarks of Monophoto and Intertype Fotosetter. The Linofilm is a phototypesetting machine developed by the Linotype Corporation. The Photon machine, invented by the Frenchmen René Higonnet and Louis Moyroud, using an electric typewriter connected with a computer and a photographing unit, is noteworthy. Almost exclusively electronic, it can deliver justified type on film in a wide variety of styles at extraordinary speed.
Today photocomposition has been adopted in lithography, gravure, and letterpress printing, and its use, together with other electronic techniques, has revolutionized the printing industry (see optical sensing). In recent years some newspapers have started to use pagination systems, in which newspapers are electronically composed by computer, output to a negative, and a plate is made of the negative.
Many reproduction processes other than those cited above have also been developed. Xerography, or electrostatic printing, has been widely adopted for photocopying; it is also the basis of the laser printer, one type of computer printer. It is also an effective means of producing master plates for offset printing. One xerographic device is used for making full-size reprints of out-of-print books from microfilm. Other duplicating processes of commercial importance are the Multigraph, which operates on the letterpress principle; the Multilith, basically a small offset press; the Ditto, a duplicator using a special fluid to remove ink from the master plate and transfer it to the paper; and the well-known photostat process. The development in the 21st cent. of machines for on-demand printing (using xerography) now allows an individual to print an appropriate computer file as a bound book in a retail store in a matter of minutes.
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