magyar term (edited): raszteres m�lynyom�fel�let

Photogravure is a process for reproducing a photograph in large editions. It uses gelatin to transfer the image from a black and white negative to a copper printing plate. The gelatin carries the image because it hardens in proportion to its exposure to light. Areas of the gelatin not exposed stay soft and can be dissolved away in water. What remains is a gelatin version of the image which is then pressed onto a copper plate. The plate is placed in an acid bath. Where the gelatin is thick, the acid eats the metal away slowly, where the gelatin is thin or absent, the acid eats faster. Thus the plate is etched to different depths according to the tones of the original image. When inked for printing, the varying depths hold different amounts of ink.