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a photomechanical process for the printing of illustrations from letterpress printing plates; it is accomplished by means of the photographic transfer of the image onto a plate made of zinc or another substance, the surface of which is then subjected to acid etching in the nonprinting sections.
Zincography was first proposed by F. Gillot in France in 1850. He developed the gillotype method, which consists in the manual application of an acid-fast image on a zinc plate and the subsequent deepening of the nonprinting sections by etching in nitric acid. In 1862, H. James in Great Britain replaced the manual application of the image with a photocopying process from a negative onto a zinc plate covered with a light-sensitive layer. The method was called photozincography, and its basic principles are still in use. However, the methods of Gillot and James were suitable only for the reproduction of monocolor line images. A screen for use in zincography was proposed in the early 1880’s almost simultaneously by S. D. Laptev, V. K. Anfilov, E. K. Anfilov, and A. Delivron in Russia and by G. Meisenbach in Germany; the production of plates from halftone originals was later shown to be possible. At the same time, methods were developed for the production of plates for multicolor printing. Zincography is also used to produce plates combining illustrations and text.
The production of plates usually consists in photographing the original, copying the negative onto the plate, etching, and finishing the plate. The original to be reproduced is photographed to a given scale by a photocopying machine. The negative produced (a line negative from a line original or a screened negative from a halftone original) is copied onto a zinc plate (or, less often, a magnesium or copper plate) covered with a copying layer, composed of a polymer, such as polyvinyl alcohol, and a chromate. A photopolymerization composition is sometimes used as the copying layer. The sections of the negative corresponding to the image elements (the future printing sections) are tanned (rendered insoluble in water) by the action of light passing through the transparent sections of the negative. After developing, which removes the nonilluminated layer from the nonprinting sections, an acid-fast image is produced on the plate, consisting of lines and screen dots. The required depth in the nonprinting sections, which depends on the distance between the printing sections, is achieved by etching on an etching machine. Line plates are usually etched to a depth of 0.04–1 mm; screen plates are usually etched to a depth of 0.035–0.12 mm. A test print is made from the prepared plate in case it is necessary to correct defects on the plate, and the plate is then set on a base.
In the reproduction of color originals, four color-separated plates are usually made, each of which transfers only one color: yellow, magenta, cyan, and black (or gray). A multicolor image is produced by consecutive printing with the four colors. The production of plates combining illustrations and text entails copying from mounted negatives of both illustrations and text; the latter is produced on phototypesetting machines. The production of photopolymer printing plates may also be considered a zincographic method. Electronic engravers are also used to make metal or plastic letterpress plates.
In Russian, the term tsinkografiia (zincography) is also used for an enterprise or shop specializing in the production of letterpress printing plates.
REFERENCESNotkina, N. M. Tekhnologiia fotomekhanicheskikh protsessov. Moscow, 1969.
Geodakov, A. I. Proizvodstvo klishe. Moscow, 1972.
Siniakov, N. I. Tekhnologiia izgotovleniia fotomekhanicheskikh pe-chatnykhform, 2nd ed. Moscow, 1974.
N. N. POLIANSKII