A reproductive process used primarily for photographs from the 1880s to the 1950s, utilizing small dots of variable size in relief to reproduce tone in the prints. The process involves re-photographing a photograph through a ruled screen, which creates a negative image made of dots of variable size. A relief halftone block is prepared by printing the negative face down on a copper plate coated with fish glue or bichromated gelatin. The unexposed areas remain soluble after development and are washed away; then the plate is acid etched and used in a printing press. From the end of the 19th century onwards, halftone was the principal means of reproducing photographs in printer's ink where long print runs are required and high quality is not of paramount importance. The principle was first suggested by William Henry Fox Talbot in 1852; it was developed commercially in the 1880s.
