A photogravure is a photographic image produced from an engraving plate. The process is rarely used today due to the costs involved, but it produces prints which have the subtlety of a photograph and the art quality of a lithograph. In essence, the production of a photogravure consists of three steps: taking the picture; producing a printing plate of the image; and printing the image on paper.
The basic process, also called photogravure, was developed in the
1850s. After taking a picture, a glass transparency is made from the negative. Next, a copper engraving plate is dusted with grains of bitumen and heated so that the bitumen becomes attached to the plate. A carbon print which has been exposed beneath the transparency is then transferred to the plate. The plate is then bathed in warm water which causes the unexposed gelatin of the carbon print to be washed away, leaving the image in relief. Ferric chloride is then applied to the plate and eats into the copper in proportion to the highlights and shadows of the gelatin relief. The result is an etched copper plate of the original photographic image.
The final step, printing, involves spreading ink evenly across the plate and then pressing the plate onto the paper. The combination of the chemical and mechanical process produces an image both warm and precise. A photogravure looks like a photograph but is a series of connected lines, rather than unconnected dots as in a photograph. The rich sepia ink and handmade paper used for the Curtis photogravures are the final elements in the production of the beautiful art prints of The North American Indian.