Technique of Photogravure

 

Photogravure and aquatint are related, because the process of producing a photogravure is derived from that of the aquatint. Both have in common the use of a copper sheet prepared by melting fine asphalt dust in the format of the sheet to be printed. The way the image is transferred to the plate is different: mechanically with the aquatint, photomechanically with the photogravure. The subsequent acid etching process is the same for both processes. After etching, the lines and surfaces that make up the overall picture appear on the printing plate as deepened sections that absorb the printing ink and release it back to the paper.

The image template for a photogravure is always a photo, usually a black-and-white negative, rich in contrast and of the best technical quality. From this, a halftone film is produced. Under this film, light-sensitive pigment paper is exposed. It is a paper that is coated with a layer of gelatine, dyed with a fine red-brown pigment. The exposed pigment paper is placed in cold water for a few minutes and, as soon as it starts to become soft, it is squeezed with the gelatine face down on a pre-prepared aquatinta plate.

The plate is then placed in warm water. Not only does the paper detach itself, but all unexposed parts of the gelatin layer are dissolved and washed away by gentle swinging the tray filled with the water. Finally, a delicate relief remains on the aquatinta plate. It consists of exposed chromatized gelatine.

Subsequently, the plate is etched in several steps, using one after the other etching baths of different acid concentrations (ferric chloride solutions). The solution first penetrates through the thin layers of the relief. It etches the copper deepest. Gradually, the solution penetrates the thinner layers of relief. More and more areas start to etch, and so the lineatures and surfaces of the image to be printed on the plate gradually become more and more visible. They appear as craters, as if engraved into the metal. The different depth of the etching corresponds to the richness of tonal gradations that will show up on the printed photogravure.

When the etching process is complete, the plate is washed off and a first print is made. Corrections and retouching are still possible. If the plate is flawless and has the desired expressiveness and depth, the edition is printed. For the printing of larger runs, starting from about ten prints, the plate has to be harden. The fine-grained surface of the plate would not withstand the run of a larger number of sheets.

The artist can intervene in several stages in the process of the creation of the heliogravure, modify the result, subject it to his creative will, namely during the photography, during the development of the halftone film, during the exposure of the pigment paper, during the etching of the metal and finally by the application of additional techniques, e.g. the dry point

back