photoengraving

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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photoengraving

Any of several processes for producing printing plates by photographic means (see photography). In general, a plate coated with a photosensitive substance is exposed to an image, usually on film; the plate is then treated in various ways, depending on the printing process to be used. Photoengraving is particularly useful for reproducing photographs via the halftone process. See also offset printing.