The Calotype Process
Supported by the Scotiabank Photography Program at the National Gallery of Canada.
William Henry Fox Talbot (1800–1877) made enormous contributions to the discovery and development of photography in the early 19th century. His work arguably serves, in fact, as the foundation for modern photographic systems. An accomplished scientist, chemist and scholar from the United Kingdom, Talbot was determined to find an alternative way of recording the natural world, without relying upon an artist’s direct hand. He began experimenting with light-sensitive chemical solutions, and developed the “photogenic drawing” process in 1834. 1 While still in its infancy, the process became a catalyst, both for Talbot’s “calotype” paper negatives and his “salted paper” prints.
Photogenic drawing was a relatively straightforward process. A piece of high-quality writing paper was first washed with a solution of sodium chloride (table salt), left to dry, then evenly coated in the dark with a solution of silver nitrate, and left to dry once more. When objects such as lace or ferns were placed on the sensitized side of the paper and exposed to sunlight, a negative silhouette would be created. Exposure times were fairly long, and areas not protected from the sun gradually darkened. Since the silver deposits on the paper reacted and changed tones during exposure, this was called a “printing-out” process. The print would then be washed in another solution of sodium chloride, which stabilized the image and reduced its sensitivity to light.2
In 1840, Talbot incorporated additional chemicals and treatments to increase the paper’s light sensitivity, permitting exposure within a camera obscura. He called the resulting image a “calotype” (derived from the Greek word kalos, meaning “beautiful”), and patented the process in 1841. 3 Unlike photogenic drawings, the calotype negative was a “developing-out” process, in which exposure to light produced a latent image that became visible only after developing the paper with additional chemicals.
Talbot’s original calotype recipe followed this five-step process:
Iodize a sheet of writing paper by applying solutions of silver nitrate and potassium iodide to the paper’s surface under candlelight. Wash and dry.
Sensitize the same surface using a “gallo-nitrate of silver” solution.4
Dry the paper and load it into a camera obscura. Expose to light.
Remove the paper and brush it with the same sensitizing solution to develop or “bring out” the image to the desired density.
Rinse the negative with water, wash it with a solution of potassium bromide, and rinse it again before laying it out to dry. Talbot would later change this fixing solution to hyposulphite of soda (a recommendation of Sir John Herschel, who was another prominent figure in the early development of photography.5)
Salted paper printing, like photogenic drawing, created positive prints from these paper negatives. Given that the chemicals were embedded directly into the photograph’s paper fibre substrate, the process produced softer images with warmer tones and matte finishes. Although Talbot’s processes did not result in the same type of image quality, aesthetic, and stability as a daguerreotype, the strongest attribute of Talbot’s method was that multiple prints could be produced from a single paper negative.
While other photographers would go on to experiment with, and modify, Talbot’s original paper processes, by the latter half of the 19th century they had been superseded by wet-plate collodion negatives and albumen printing. These surviving negatives and prints are incredibly delicate, and require careful storage and handling to ensure their continued preservation.