Another post here discusses photographic daguerreotypes, so let’s now look at the next step in the development of photography.
Whereas the daguerreotype produced a negative image on a metal base, an ambrotype created a positive image on glass. The ambrotype is a variation of the wet plate collodion method introduced by Englishman Frederick Scott Archer in 1851.
For the wet plate collodion method, a glass plate was polished and coated with a thin layer of iodized collodion before being dipped in a bath of silver nitrate solution for three to five minutes. Once it had drained and dried, it was placed in a plate holder with a dark slide to protect it from the light.
The prepared plate was loaded into the camera while still wet and the dark plate removed to begin exposure, which could take as little as five seconds, or well over a minute, depending on the light and conditions of the day. Once done, the dark slide was replaced and the plate removed from the camera for immediate treatment – it could not wait or the image would be lost. It would be developed using a ferrous sulfate developer, and the image would be fixed with potassium cyanide or sodium thiosulphate solution before being rinsed and varnished.
The resulting image looked like an underexposed negative, but would appear as a positive when viewed against a dark background. The dark areas of the image appeared as clear patches on the plate while the lighter areas of the image showed opaque. The glass plates were often painted black on one side or mounted against black velvet to make the image easier to see. They were monochrome but could be hand coloured.
Another plate of glass would be mounted over the emulsion side before the plates were mounted within a metal frame and housed in a case, just as daguerreotypes were.
Ambrotypes were significantly cheaper to create than daguerreotypes. The plates did not need to be polished or fumed, which reduced equipment and material costs, and they were made out of much cheaper glass rather than expensive silver-plated copper. It was also possible to photograph more clients per day, due to the reduced exposure time.
There were, however, disadvantages. The technique required great dexterity as the whole process had to be completed within 10 minutes before the plate dried, so ambrotypists had to have a dark room immediately available. Travelling ambrotypists would take a tent or portable dark room with all the associated chemicals with them.
The nitrate bath solution could leave stains on clothing and furnishing, and the plates could leave nitrate residue in the camera. An overload of nitrate could be potentially explosive.
The photograph fixer, potassium cyanide, was a powerful, deadly poison, and occasionally caused cyanide poisoning. It was even drunk by one photographer to commit suicide.
Ambrotypes were still relatively quick and significantly cheaper than daguerreotypes and became immensely popular between 1855 and 1865. There are many more ambrotypes than daguerreotypes surviving today, 32 of them in the Whanganui Regional Museum collection.
Sandi Black is the Archivist at Whanganui Regional Museum.