'Portrait of Two Unidentified Women'
Museum no. PH.167-1929
This image is an example of the daguerreotype.
The daguerreotype was invented by Louis-Jacques-Mandé Daguerre and introduced to the public at a meeting of the French Academy of Sciences in Paris on August 19, 1839.
The daguerreotype image was easily damaged by touching, and was protected in a case or frame, with a decorative mask or matt and a cover glass.
Since the image is in the form of a greyish-white deposit on a shiny silver surface, the daguerreotype has to be held so as to reflect a dark ground against which the image is seen as a positive. If the image reflects a light ground, the image appears negative. This is unique to the process and is the most easily recognised feature when the daguerreotype is in a case.
The daguerreotype is a direct-positive process, creating a highly detailed image on a sheet of copper plated with a thin coat of silver without the use of a negative. Highly polished silver-plated copper sheets are treated with iodine to make them sensitive to light. After they are exposed in a camera, the sheets are developed with warm mercury vapor until the image appears. To fix the image, the plate was immersed in a solution of sodium thiosulfate or salt and then toned with gold chloride.
Exposure times for the earliest daguerreotypes ranged from three to fifteen minutes, making the process nearly impractical for portraiture. Modifications to the sensitization process coupled with the improvement of photographic lenses soon reduced the exposure time to less than a minute.
This photograph can be found in Print Room Box 12a.