Photomechanical Processes



A process that first exposes a sheet of bichromated gelatin under a negative. After exposure, washing the sheet in warm water produced a relief, from which a gutta-percha mould is made. This is then used to make an electrotype plate that is printed. Invented by Paul Pretsch and patented by Duncan C. Dallas in 1855.


Includes most photoetchings (see below), and also known as "gravures." Invented in 1878 by Karl Klic of Bohemia. A carbon tissue (coated with bichromated gelatin) is exposed under a positive transparency. This tissue is pressed into a metal printing plate which has been dusted with resin. The plate is washed to remove the tissue and the unexposed gelatin (under the shadows of the transparency). The plate is then etched, and the acid bites into the plate where the gelatin was washed away. After etching, the plate is inked and printed. The shadows of the transparency correspond to the shadows on the print. The prints contain a fine, irregular grain pattern from the resin.


Developed from the photogravure process, rotogravures use a screen of fine lines intersecting at right angles rather than the resin dust. Additionally, a printing cylinder is used instead of a printing plate. The prints contain the screen pattern of intersecting lines. Introduced around 1895 by Karl Klic and commonly used for newspaper illustrations. (1)


While most photoetchings are actually photogravures (see above), the first photoetchings were produced instead by heliographs. Joseph Nic¨¦phore Ni¨¦pce intended heliography to be an intaglio printing process, and he exposed a pewter plate sensitized with bitumen of Judea directly under an oiled engraving. The plate was then washed with oil of lavender, leaving the hardened bitumen on the plate. The plate was then etched, and the acid bit into the plate where the bitumen was washed away. After etching, the plate was inked and printed, creating a positive image.

Ni¨¦pce also attempted to produce printable heliographs by exposing sensitized pewter plates to the view of nature through a camera obscura. The World's First Photographis the only surviving product of this unsuccessful attempt.



This process uses the same principle as lithography: the rupulsion of oil and water. A stone, or a metal plate (either zinc or aluminum) is coated with bichromated gelatin and exposed under a negative. The plate is then washed, and this produces a relief where the exposed gelatin remains and the unexposed gelatin is washed away. The plate is then inked, and the ink adheres to the hardened gelatin and not to the wet plate. The highlights of the negative, therefore, produce the shadows on the print, creating a positive image. Introduced in 1858.


A type of photolithograph where a glass plate replaces the stone or metal plate. The glass plate is coated with two layers of gelatin, the top one being bichromated. Exposed under a negative, the top layer hardens where it has been exposed. The plate is washed, the unexposed bichromated gelatin runs off, and the gelatin from the base layer absorbs the water producing a finely veined pattern of wrinkles, or reticulation. Within this reticulation, the grooves are hardened gelatin, and the bumps are wet gelatin. The ink adheres to the grooves and not to the bumps. The plate is then printed. Introduced in the 1860s, collotypes have had a variety of names such as Albertype, Lichtdruck, phototype or phototypie, and heliotype. (5)



Refers to the production of relief printing surfaces with the aid of photography.

Halftone photomechanical prints

A photomechanical process in which the image is broken up into a regular pattern of dots of varying sizes when rephotographed through a screen. When the printing plate is etched, the dots are left in relief. The ink adheres to the dots, and the shadows in the original translate to the larger black dots in the final print. First commercially available in the 1880's.


Also called "photoglyptie." A mechanical method of producing carbon prints developed by Walter Woodbury in 1865 that uses both intaglio and relief techniques. A gelatin relief is prepared by a bichromate process and then pressed into a lead sheet under very heavy pressure. The lead mold is then filled with pigmented gelatin (creating a transferable carbon print), pressed onto a paper support, trimmed, and mounted. Widely used for fine book illustration from about 1875 to 1900, it is often indistinguishable from a carbon print.

Ink jet prints

Nonimpact computer-controlled prints in which tiny droplets of ink are projected from nozzles onto paper.

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