Photogravure
From Free net encyclopedia
Photogravure is a type of intaglio printing process used for reproducing monochromatic (black and white) images. Image:TimothyDwightV.jpg In the late 19th century and early 20th century photograuvure was frequently used for reproducing a photograph in a book or magazine.
Though it is no longer widely used, its primary use today is for reproducing fine art photographs. It is called photogravure because it involves a photographic engraving process.
The process was invented in 1879 by Czech photographer Karel Klíč.
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Photogravure Process
This is a generalized description of the photogravure process. Techniques and materials vary greatly.
Engraving
A film positive is made from the original photographic negative. This positive is placed on top of a photo-sensitive gelatin tissue, and the sandwich exposed to UV light. The light travels through the positive, hardening the gelatin in proportion to the degree of light exposed to it. The gelatin tissue is adhered to or 'laid down' onto the copper plate. A hot water bath allows the tissue backing to be removed and then washes away the soft gelatin in relation to the exposure, forming a resist on the copper plate. The plate is etched in a bath of ferric chloride. The etch corrodes the copperplate in relation to the thickness of the gelatin. Thus the image gets etched onto the copperplate by the acid, creating a gravure plate.
Printing
Ink is applied to the surface of the plate. The plate then gets wiped with tarltans, removing excess ink and leaving ink only in the recesses. The plate is then run through a press with a sheet of dampened paper, and the ink transfers from the recesses to the paper, creating a printed image.