Photoengraving
Collier's New Encyclopedia (1921)
a term applied to producing printing blocks or plates by photography. The most commonly employed process is to coat a metal plate with a thin film of asphaltum, and expose it to light under a reversed positive. The picture is next developed by dissolving away the parts of the asphaltum not acted upon by the light, and the plate is subsequently etched in the usual way. This process is sometimes called photoaquatint. The second method is more elaborate. A film of bichromatized gelatine, on a sheet of glass or a copper plate, is exposed under a photographic negative, and the unprinted portions which are soluble in water washed away, leaving the printed parts in relief. The plate with the relief is next coated with a film of silver by electro-deposition, and placed in an ordinary electrotyping bath, in which it is allowed to remain till a shell of copper from one-sixteenth to oneeighth of an inch thick (according to size of plate) is formed. This, after the rough excrescences have been removed by filing, becomes the printing plate. It can be worked upon by an engraver, if necessary, to remove photographic defects, and is printed on a copper-plate press. When a relief block is required, a reversed negative is used to print from, and the etching is carried to a much greater extent. These processes answer for su subjects in black and white, as well as in colors. This is also the system by which conversion of the half-tones of a photograph into an ordinary printing block or plate has become so eminently successful. See PHOTOELECTRO- TYPE; PHOTOGRAVURE.
What Has Changed in the Last Century
When Collier's wrote this in 1921, coating plates with asphaltum or bichromated gelatine and etching them in acid was the everyday way to get a photograph onto a press, and the halftone block it describes was the backbone of newspaper and magazine illustration. Letterpress halftones were displaced after the 1950s by offset lithography, and the etching bath itself disappeared once computer-to-plate systems, from the 1990s on, began imaging plates directly from digital files with no camera, negative or acid at all. Photoengraver, a skilled union trade with its own apprenticeships through the mid-twentieth century, has effectively ceased to exist as a job. The chemistry survives mainly among letterpress hobbyists, who use light-sensitive photopolymer plates rather than copper.
Written for this edition, 2026.