photoglyphic engraving

Photoglyphic engraving, a term coined by Henry Talbot (1858) to described his photo-etching process (patented 1852 and 1858), using dichromated gelatin as an etching resist on a plain copper or steel-faced plate. Talbot experimented with a ferric chloride etching bath and later proposed an aquatint grain (c. 1856), contributing to the subsequent development of photogravure. He also patented the principle of a screen (initially of muslin, later of ruled lines on glass) through which the plate was exposed; this method of obtaining shadow density led to the half-tone process.

— Hope Kingsley