Glossary

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Gelatin dry plate negative

Distinguished from the wet collodion negative and the dry collodion negative, the gelatin dry plate negative refers to thin plates of sheet glass coated with a gelatin emulsion made light-sensitive by silver salts. The first really practical dry plate negatives were invented in 1871 by Richard Leach Maddox and, following rapid improvements, were the most common type of negative in the mid-1880s. Dry plate negatives could be purchased precut for individual cameras, were more sensitive to light, and freed the photographer from an on-site darkroom and the messy last-minute chemical preparations of the wet collodion negative. The ease and popularity of the gelatin dry plate negative was eventually surpassed by that of the gelatin silver paper negative and the gelatin silver negative on celluloid roll-film, introduced in the late 1880s.

Gelatin silver print

The generic name for the common black-and-white photograph. The process has been the main photographic printing process since its introduction in the late 1880s. Paper is coated with an emulsion of light-sensitive silver halide in gelatin. To produce a print, the paper is exposed under a negative, either by contact-printing or through an enlarger, then chemically developed, stopped, fixed, and dried. Gelatin silver prints are normally black-and-white, although they can be toned with various compounds or minerals to produce a wide range of hues. In addition, various commercial papers will also impart warm or cool tones to the black-and-white print.

A variation of the gelatin silver print, the silver bromide print is printed on a commercial paper with a bromide silver emulsion. This chemical process, available in the 1880s, was used for contact prints or enlargements by artificial light. Bromide prints have a baryta layer, a porous substance that produces tinted or clear white highlights. Usually toned with copper, these prints range from reddish-purple, brown, or slate to warm blacks.

Chloro-bromide prints are still another variation of the gelatin silver print. First introduced around 1883, they are printed on chloro-bromide paper with an emulsion containing both silver chloride and silver bromide, producing a warm, black-toned, sharp image. Chloro-bromide prints were often toned different colors, including red, blue, or purple and were favored by pictorialist photographers. See also developing-out paper (d.o.p.).

Gum bichromate print

A print made with a technique that relies on a coating of pigmented gum arabic and potassium or ammonium bichromate, which allows the photographer to manipulate the printed image during development. The coating is brushed on a piece of drawing paper. When it is dry, a negative is placed on top of the paper and exposed to light. A viscous and light-sensitive material, gum bichromate does not respond to light by darkening, as silver compounds do, but by hardening. The amount of light striking an area determines the hardness of the gum arabic coating in that area. After exposure, the print is washed thoroughly in warm water, creating dark areas where the gum arabic has become hard and light-toned areas where it washed off. The photographer can further manipulate the image by removing more pigmented gum arabic with brushes or a stream of water during the washing stage.

A prototype of the gum bichromate print, using pigment and gum arabic with potassium dichromate, was exhibited in 1858 by the Englishman John Pouncy, but the technique was not fully developed until the last decade of the century. It was popular with photographers until the 1920s.

Gum platinum print

A print that has a layer of gum bichromate printed in registration over an initial platinum print.

Instantaneous photography

A term that generally refers to photographs with extremely short exposure times, especially those of less than one second, that "freeze" motion.

Kodachrome

See chromogenic process color print.

Lumière autochrome

See additive color process color plate.

Mat/mount

A mat is a piece of good quality card or paper stock with an opening cut to expose the photograph. It is attached to the mount with a paper hinge. A mount, also cut from good quality card or paper stock, is a secondary backing or support for a photograph, other than the primary support of the paper on which the image is printed. Both serve to exhibit and protect the photograph.

Mixed media

The technique of combining photographic images with other materials on a common support. A mixed-media piece can include fragments of various graphic media, such as etching or lithography, with pencil or pen and brushwork applied directly to the surface. See also collage/montage.

Multiple exposure

The intentional exposure of a negative in a camera more than once to produce a combination of images in a single print of that negative. The accidental double exposure of film is an all-too-familiar variant of this effect.

Negative print

The opposite of a positive print, in which the tonal values are reversed shadows appear light and highlights dark. Negative prints can be made by various methods, such as placing photographic paper instead of film in the camera, photographing a negative, or printing from a positive transparency.

Oil print

A print produced in pigment or ink applied with a brush, based on the principles of lithography (the repellent action of oil and water). A sheet of paper coated with a gum emulsion or gelatin and made light-sensitive with potassium bichromate is exposed to sunlight under a negative. The emulsion hardens where exposed to light and rinses off in where light could not penetrate. The areas that wash away are then colored with pigment or ink, and the amount of water retained by the emulsified surface determines the density of color on the image.

From the 1860s to 1910, many processes were invented for printing images in pigment rather than silver and other metals. The oil pigment process was appealing because images in pigment are essentially permanent. They are not susceptible to the fading, discoloration, or deterioration common in silver prints and, because of their color range, look like work in other media such as crayon, charcoal, or watercolor.

The Rawlins oil pigment print, a variation of the oil print, is made on a sheet of paper coated with a gelatin or gum emulsion, sensitized to light in potassium bichromate, dried, and contact-printed under a negative in sunlight. After exposure it is washed and placed on wet blotting paper for the pigmentation stage, where pigment or ink is applied with a special brush. The color penetrates the areas that have absorbed the water (the shadows), not those made water resistant by the hardened gelatin (highlights). The look of the final print depends on how much pigment or ink is applied, either over the entire surface or only to specific areas. The process was invented by G. E. H Rawlins (active 1900-1920s) in 1904.

The look of the final print depends on how much pigment or ink is applied, either over the entire surface or only to specific areas. The process was invented by G. E. H Rawlins (active 1900-1920s) in 1904.