Photoengraving and photolithography

Photoengraving and photolithography, processes by which plates or cylinders containing matter for printing are created. Techniques of photographing and etching (acid engraving) replicate illustrations and drawings to be printed in the photoengraving process. In this method line engravings reproduce lines and halftone engravings reproduce continuous ranges of tone. Photography is used to transfer printed matter to the printing plate. The body of text to be printed is then treated with water that will accept the oily ink from the rollers, while the unprinted portions of the plate are treated with an oil that accepts only water from the rollers.

See also: Engraving; Lithography; Printing.