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printing, 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.
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.
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.
Illustrations and Color 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.
An excellent selected bibliography is H. Lehmann-Haupt, One Hundred Books about Bookmaking (1949). See W. Chappell, A Short History of the Printed Word (1970); L. Febvre and H.-J. Martin, The Coming of the Book (1976); E. Eisenstein, The Printing Press as an Agent of Change (1979) and Divine Art, Infernal Machine (2010).
(offset lithography), a method of printing in which the ink impression is transferred from the printing plate to an intermediate rubber-coated surface, or blanket. The image is then transferred from the blanket to paper or some other printing material. Offset was first used in the United States, where the first offset press was built in 1905.
The term “offset” usually designates those printing processes that use planographic plates and that are based on the coating of the image, or printing, areas with ink and the non-image, or nonprinting, areas with an aqueous solution that is not ink receptive. During printing, the plate is alternately coated with an aqueous solution and roller-coated with ink. The plate then makes contact with the surface of a rubber blanket, which in turn is brought into contact with paper to produce a print. Thus, a double transfer of the image occurs without the paper ever coming into direct contact with the plate. This lessens significantly the amount of pressure required during printing and, thereby, increases the wear resistance of the plate. In turn, productivity is higher, as is the quality of reproduction.
Offset involves photomechanical and electronic processes during platemaking, as well as mechanized and automated processes during the preparation of the plates and printing. The plates are aluminum or zinc sheets that vary in thickness from 0.35 to 0.8 mm. Their surface is grained to obtain a uniformly mat surface. The printing and nonprinting areas on the surface of the plates are produced by light-generating films, which differ in terms of molecular surface properties and which are receptive to either water or ink. Aluminum plates are subjected to a complex electrochemical preparation in automated lines to increase their adsorption capacity and wear resistance. Composite plates consist of two metals, one of which is extremely ink receptive and forms the printing areas (such as copper), while the other is naturally water receptive and forms the nonprinting areas (nickel, chromium, or stainless steel). Composite plates are used for long-run printing in high-speed presses owing to the high hydrophily and wear resistance of the nonimage areas. Composite plates are usually produced on an aluminum or steel base, and galvanic methods are used to coat the entire surface with copper film having a thickness to 10 μ or with chromium film with a thickness of 1–3 μ. The printing image on either monometallic or multimetallic plates is produced photochemically by projecting an image through a photographic negative or positive onto a light-sensitive coating of the plate. Such a coating consists of high-molecular compounds (albumin, gum, polyvinyl alcohol), chromium salts (diazo compounds), and film-forming substances or photopolymers. When exposed to light, chromium salts harden. Thus, the exposed areas of the coating harden and are rendered insoluble in water. The exposed areas of the coating are shielded by the opaque parts of the negative or positive. The coating is subsequently removed, with the printing image fixed on the plate.
More widely used are coatings based on diazo compounds, in which light causes photochemical decomposition on the exposed portions, leading to the removal of the coating from these areas of the plate during developing. The areas of photopolymeric coatings exposed to light polymerize and become insoluble in water. The coating is removed from the nonilluminated areas of the plate during developing. Coatings consisting of both diazo compounds and photopolymers may be applied in a thin layer on monometallic and multimetallic plates; the layer remains unchanged for a long period of time (more than a year). This makes it possible to prepare the metal and presensitize the plates in special plants.
In the production of presensitized plates, the printing areas on monometals are produced on the coating, which has been shielded during copying by the opaque portions of the photographic positive and which is retained after development of the copy. The coating on multimetallic plates is removed from the printing areas after developing and remains as a temporary protective layer for the nonprinting areas. Chemical or electrochemical etching of the top metal (nickel or chromium) is done down to the copper layer; the protective coating is then removed from the nonprinting areas. In this case, the printing areas are produced on the copper, and the nonprinting areas on the nickel or chromium. All methods of platemaking require that, after the production of the printing areas, the nonprinting areas be treated with a water-receptive solution. This imparts stable water-receptive properties to the areas.
Operations required for the processing of monometallic plates (developing, washing, and drying), are performed separately by mechanized equipment. The production of prints and the preparation of multimetallic plates are carried out on continuous production lines.
Offset prints are produced by offset presses. Each working cycle of a press consists of coating the printing plate, rolling the ink onto the printing areas, feeding the paper into the press, printing, and removing the finished print from the press and placing it on the receiving table.
Offset is popular owing to the mechanization of platemaking and the high productivity of the presses. It makes possible the reproduction of all types of publications.
REFERENCESSiniakov, N. I. Tekhnologiia izgotovleniia fotomekhanicheskikh pechatnykh form. Moscow, 1966.
Nikanchikova, E. A., and A. L. Popova. Tekhnologiia ofsetnoi pechati. Moscow, 1966.
Zakharov, A. G., and D. A. Fufaevskii. Ofsetnye mashiny i rabota na nikh. Moscow, 1972.
A. L. POPOVA
E.g. the Perl function splice(ARRAY, OFFSET, LENGTH, LIST) replaces LENGTH elements starting at index OFFSET in array with LIST, where offset zero means the start of the array.
For an Intel x86 processor with a segmented address space the offset is the position of a byte relative to the start of the segment.
offset(1) See offset press.
(2) The distance from a starting point, either the start of a file or the start of a memory address. Its value is added to a base value to derive the actual value. An offset into a file is simply the character location within that file, usually starting with 0; thus "offset 240" is actually the 241st byte in the file. See relative address.
(3) In word processing, the amount of space a document is printed from the left margin.