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.
A. IA. MANTSEN