Daguerreotype vs. Calotype (by HCM)

The daguerreotype and calotype are the foundations upon which the modern practice of photography is based....

The Daguerreotype: This process was invented in the 1830s. It involves directly exposing an image onto a cooper plate coated with iodized silver would produce a lasting image if it was also exposed to mercury vapor and fixed in a salt solution.

a daguerreotype

The Calotype: Talbot's process, patented in 1841,  involves photographic paper that is brushed with salt solution, dried, then brushed with silver nitrate solution and dried again, creating a silver chloride.  The addition of garlic acid made the paper more sensitive to light. After exposure, the image is fixed with another iodized solution. To make a print, the negative is placed on top of a more photo paper, laid flat on a glass frame and allowed to develop in the sun.

a calotype

Differences: The daguerreotype is a negative image, but the mirror surface of the metal plate reflects the image to make it appear positive. The calotype negative had light and dark tones reversed, like negatives today. Unlike the daguerreotype, the calotype's negatives could produce an unlimited number of prints. The second big difference is how the image was fixed. Daguerre used metal plates, a revolutionary process that was quickly deemed cumbersome. Talbot used paper to capture the image, as described above.

Similarities: Both processes utalized silver and iodine to make the materials light-sensitive. The paper used for the calotype would be washed in a silver nitrate solution and later a potassium idoine solution. The copper plates in the daguerrotype process was exposed to iodine fumes, which reacted with the copper to form silver iodine. The processes share a similarity in exposing the images; the time frame for taking picture after preparing the material was short for both. Daguerreotype plates needed to be used within an hour of being exposed to the iodine fumes. Calotype paper needed to be coated with a solution of silver nitrate and gallic asid before it could be used in an exposure. once this occurred, the paper needed to be used within a few hours. In fixing the images, both processes used salt solution Sodium thiosulphate was used for calotypes and saline solution was used in daguerrotypes. Fixing washed away traces of silver so the image would not continue to darken and become overexposed.

-HCM-

Week 4