What is the Difference between a Daguerreoptype and a Calotype

Before 1884 when Kodak’s founder, George Eastman supplied flexible film for cameras, early photographers loaded a camera one wet plate at a time for each image. A Daguerreotype was a widely used early photographic process that was first announced by Frenchman, Louis Daguerre in 1839. France made it free for the whole world to use, except in England where a license had to be purchased. The product was a single photograph on a silver plate, or on a silver-plated sheet of copper or brass. No reprints were possible and the image was reversed as in a mirror, but the detail was excellent. Prior to placement in a camera, a silver plate was exposed to iodine or bromine fumes to create a light-sensitive silver salt. The plate was then exposed to an image in a camera for 10 to 30 seconds. The latent image was developed in a box of hot mercury fumes. Mercury deposited in the most light-exposed areas. The image was then chemically fixed to stop development. The resulting photograph was thin and easily damaged by even the slightest touch. For this reason, it was sealed under a glass plate for viewing. The materials for the process were expensive and, in the cases of bromide and mercury, very unhealthy for the photographer. Mercury poisoning is fatal.

The Calotype process was announced by Henry Talbot in mid-1841, but it was patented and not free to use. The detail was not as fine as a Daguerreotype, but reprints could be made. The process used a negative-to-positive design that is still used today. A chemically-treated paper was used in the camera instead of a silver plate. The paper allowed for reprints, but the fibers in the paper dulled the detail of the photo. Thus the highest quality rag-paper was necessary. Modern pulp papers could not be used because they contain bleach. Waxing the paper after image exposure helped to sharpen the detail by making the fibers more translucent. Batches of paper could be treated in advance to silver and iodide solutions and dried. Then only to within a few hours of use could the paper be sensitized with a solution of silver nitrate. Image exposure time in the camera was long, at tens of seconds to tens of minutes depending on the degree of sunlight. The latent image was developed with gallo-nitrate to a sufficient degree determined by the photographer’s judgement. Then the image was fixed with potassium bromide or hypo solution. The fixer had to be thoroughly washed away to avoid damaging the image. The resultant image looked like a negative with reverse light and dark areas. A positive image was made by passing sunlight through the negative to a second chemically treated paper.

Both processes used the principle that silver halides turn dark when exposed to light. Both used a camera obscura, a light-tight box, and had to be loaded with only a single plate in the dark. Timing of every step was critical. Both processes required a high level of expertise with chemicals and darkrooms. The Calotype process became the preferred method for several reasons. The image was warmer with matte brownish tones compared to the silvery look of a Daguerreotype. Unlimited reprints could be made compared to a single Daguerreotype. The processing chemicals were not as dangerous. The materials were less expensive, although a high initial price had to be paid on the patent. If desired, additional detail could be drawn in by hand because the image was on paper. The photo was not as fragile and can be viewed from any angle. Succeeding photographic imaging technologies proceeded along the Calotype principle of a negative to a positive image.