Gelatin Dry Plate

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Gelatin Dry Plate Overview

Common Use Dates: 1880 - 1925

Alternate Names: Gelatin Silver Dry Plate; Gelatin Silver Glass Plate Negative; Silver Gelatin Glass Plate Negative

Key Identifying Features

Mistaken For: Wet Plate Collodion

Process Family(s): Photographic

Description

The gelatin dry plate process is based on the light sensitivity of silver halides, which are suspended in a gelatin binder on a glass support. The process was used to make both negatives and positive transparencies, popularly known as lantern slides. Richard Leach Maddox was the first to successfully make a gelatin dry plate negative in 1871. The process underwent many improvements by a variety of people before it was commercially viable in 1879. Some of the key improvements to making silver gelatin binders included having an excess of halide (salt) in the gelatin (1874); washing the gelatin to remove excess salt and impurities (1874); a procedure called ripening in which the gelatin is heated increasing light sensitivity (1878); machine coating (1880); and finally dye sensitization extending the sensitivity beyond the blue spectrum of light to green light (commercialized in 1882) and to then to the full visible spectrum (1906). 

Gelatin dry plates were the first photographic negative materials that were manufactured and mass produced. Photography became faster, easier and the need for a portable darkroom was eliminated. The materials also had a shelf life of several months. This made photography much more accessible, allowing more people to become amateur photographers, which in turn increased demand for manufactured photographic papers. This marked the birth of the modern photographic industry. Gelatin dry plate negatives were exclusively used to print all photographic printing processes used between the 1880s and 1890s and was used into the 1920s. Printing processes included: gelatin and collodion POP, matte collodion, silver gelatin DOP, platinum, and carbon. 

Gelatin dry plate positive transparencies are commonly known as lantern slides because they were typically viewed by transmitted light using a magic lantern. Lantern slides were made in a range of processes including collodion, albumen, carbon, and woodburytype. Gelatin dry plate transparencies became popular in the 1880s and were used for a wide range of purposes including educational lectures, entertainment, and by popular camera clubs as a way to disseminate and share images with a large audience. 

To make a gelatin dry plate, the glass support had to be cleaned, polished, and treated to ensure good adhesion of the gelatin to the glass. The glass could be treated in several ways: a thin coating of hardened gelatin, dilute albumen, India rubber or soluble glass could be applied, or the glass could be chemically etched. Warm, liquid, sensitized gelatin was then poured onto the plate in a thin and uniform layer. Most coating machines had a moving belt which carried the glass under the coating apparatus. The plates were then left in a cool, flat place to dry. 
Dry plate negatives contained silver bromide crystals and required very short, in camera, with exposures of about one second or less. Transparencies may have faster silver bromide crystals which produced neutral tones or silver chloride crystals, which were slower and produced warmer tones. Transparencies were either contact printed, reversal processed, or produced by re-photographing a negative with a copy camera. 

During exposure a latent image was formed which was then developed, fixed, and washed in a darkroom or a darkened space. It was not necessary to develop the plates immediately. Optionally, negatives and transparencies could be intensified to compensate for under exposure or reduced to compensate for over exposure. Early plates were sometimes varnished, but after 1890 the practice of varnishing became rare.   

Initially, gelatin dry plates were only sensitive to blue wavelengths of light. In 1882, the first orthochromatic plates were available; these were sensitive to blue and green light. In 1906, panchromatic plates were introduced; these were sensitive to all colors of the visible spectrum of light. The use of a glass support for negatives began to decline by the 1890s with the introduction of flexible film (cellulose nitrate). In 1912, sheet film was introduced and by the late 1920s or early 1930s sheet film replaced glass plates entirely. The gelatin dry plate process continued to be used for spectroscopic and astronomical applications until the late twentieth century and the introduction of digital photography.