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photocopying,process whereby written or printed matter is directly copied by photographic techniques. Generally, photocopying is practical when just a few copies of an original are needed. When many copies are required, printingprinting,
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.
..... Click the link for more information. processes are more economical. However, when a printing process is used, the master or stencil required can sometimes be produced by photocopying. Principal photocopying processes include silver halide, transfer, plan, thermographic (see thermographythermography
, contact photocopying process that produces a direct positive image and in which infrared rays are used to expose the copy paper. In a specially designed machine the original is placed in contact with a copy paper containing a heat-sensitive substance.
..... Click the link for more information. ), and electrostatic (e.g., xerographyxerography
, also called electrophotography, method of dry photocopying in which the image is transferred by using the attractive forces of electric charges. A beam of light, usually from a laser, is made to strike the original material, e.g., a white page with black lettering.
..... Click the link for more information. , which has become so widespread that the process is popularly almost synonymous with photocopying). Two well-known silver halide processes, photostating (see photostatphotostat
, reproduction of any printed or simple black-and-white material, such as drawings or manuscripts, made by the Photostat, a photographic camera. While slower and more expensive than xerography, the process is still used where a high degree of resolution is desired, as
..... Click the link for more information. ) and microfilming, use cameras to make photographic copies of an original. Microfilming generates copies that are from 1/12 to as little as 1/100 the size of the originals, allowing great economy in space and materials when long-term storage is necessary. Microfilms are read by either projecting them or photographically printing them as enlargements. In transfer processes the original is placed in contact with negative paper and exposed to light. In the diffusion transfer the negative is developed while in contact with the positive. During development the chemicals forming the image in the negative diffuse to the positive, producing an image there. In gelatin transfer the negative is developed and then pressed against positive paper. A dyed gelatin on the negative is picked up by the positive, producing an image on it. Transfer methods are less expensive than silver halide processes, but the image produced by the former deteriorates with time. Plan copying is used to copy materials such as architects' drawings and engineers' plans. In one variety of plan copying known as the whiteprint process, an original is made on translucent paper. The paper is placed over a sheet coated with a diazo compound and exposed to a source of ultraviolet light. The compound covering the area that is exposed to the light decomposes. The compound shielded from the ultraviolet rays by the dark areas of the original can be developed to form a positive image. The blueprintblueprint,
white-on-blue photographic print, commonly of a working drawing used during building or manufacturing. The plan is first drawn to scale on a special paper or tracing cloth through which light can penetrate.
..... Click the link for more information. process, another method of plan copying, has been largely superseded by whiteprints, which are of better quality and cost approximately the same.
a copying process using photographic methods and equipment. Photocopying may use conventional photographic techniques to produce high-quality copies from fine-tone originals and to prepare offset printing plates, or it may use a simplified process to produce copies of texts, tables, blueprints, and drawings; in the USSR the latter category is called technical photocopying. Technical photocopying may be accomplished either by a direct method (reflex photocopying) or by a transfer method (contact-diffusion or matrix-transfer photocopying).
In reflex photocopying, copies are produced from opaque, one-sided or two-sided originals by placing the originals in direct contact with a light-sensitive material, namely, reflex (direct or reversal) photographic paper with a transparent support. The exposing light strikes the surface of the photographic material, and a second exposure from light reflected from the original is superimposed on the uniform, first exposure. Reflex photocopying is used to obtain copies of documents written in pencil and ink, as well as printed and typewritten documents. Copies on reflex films may be used as intermediates in diazo copying.
Contact-diffusion photocopying is carried out by transfer from a previously exposed special negative photographic paper onto transfer paper that is not light-sensitive. The original is exposed by the contact method on reflex negative photographic paper, which is then developed together with the transfer paper. Subsequently, the negative and transfer paper are tightly pressed together. As a result of the diffusion of silver halides in the negative to the gelatin layer of the transfer paper, a direct positive copy is formed on the transfer paper. Only one positive copy may be obtained from one negative. The process is very similar to the rapid production of positive images by the Soviet Moment (Polaroid-type) camera.
Matrix-transfer photocopying uses a special photographic paper that is converted into a matrix as a result of exposure and subsequent treatment by an activating solution (hardening development or hardening bleaching may also be used). When the matrix is laid in close contact with transfer paper, the nonexposed sections of the light-sensitive emulsion corresponding to image elements in the original release a dye, some of which is transferred to the transfer paper to form a direct positive copy. Up to ten copies may be produced from one matrix.
Photocopying may be accomplished with the aid of cameras and photocopying machines or with special equipment for contact photocopying, consisting of a copying machine, a set of baths for developing and fixing the prints, and a drying device. Photocopying was commonly used up to the 1970’s to produce copies from various types of originals. Its use has declined with the development of more efficient and inexpensive means of copying technical documents.
Microfilming is a type of photocopying.
REFERENCESZasov, V. D., and V. N. Iurin. Razmnozhenie tekhnicheskoi dokumentatsii. Moscow, 1968.
Alferov, A.. V., I. S. Reznik, and V. G. Shorin. Orgatekhnika. Moscow, 1973.
Orgtekhnika v upravlenii. Moscow, 1975.
A. IA. MANTSEN