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photoengraving,photomechanical process in the graphic arts, used principally for reproducing illustrations. The subject is photographed, and the image is recorded on a sensitized metal plate, which is then etched in an acid bath. In the case of line cuts (drawings in solid blacks and whites without gradations of color), the photoengraving is done on zinc, and the result is called a zinc etching. In the case of halftone cuts, the work is done on copper. The halftone effect is accomplished by photographing the subject through a wire or glass screen, which breaks the light rays so that the metal plate is sensitized in a dotted pattern; the larger dots create the darker areas, the smaller dots the high lights. The finer the screen, the greater the precision of detail in the printed product. Halftones made with a screen having 65 lines to the inch are considered coarse. Those having 150 lines to the inch are considered fine.
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The technique of producing relief plates such as halftones or zinc etchings by photography; a metal plate is coated with a photosensitive emulsion and exposed to light under a reversed positive; the picture is developed by dissolving away the portion of the emulsion not acted upon by the light, and the plate is etched.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.