Many images from the Clarke period are ambrotypes, from Ancient Greek word for “immortal” or “impression”. The ambrotype uses the wet plate collodion process, invented by Frederick Scott Archer (1813-1857) of England, to generate a negative image on a sheet of glass. Archer's process was adapted by James Ambrose Cutting (1814-1867) of Boston in 1854, who took out several patents in the United States and used the plate image produced as a positive, rather than a negative.
|Cased ambrotype from the collection of The National Society of The Colonial Dames of America in the State of Illinois, housed at Clarke House Museum|
Ambrotypes are produced by covering a small pane of glass with a thin layer of collodian dipped in silver nitrate. The sitter is positioned by the photographer and the wet plate is inserted into a camera. The plate is exposed to the light from five to sixty seconds depending on lighting conditions, developed, and fixed. The resulting image is, in fact, a negative. However, when placed against a dark background it appears to be a positive image. Areas of clear glass are viewed as dark because of the backing and the exposed areas, opaque because of the effects of the chemical solution, appear light.
Images of this type were often coated with black paint or varnish or placed against black paper or cloth. This can be done to either the emulsion-coated side of the plate or the clean glass. If the clean glass is backed, the thickness of the glass and emulsion produce an illusion of depth.
|The back of the glass plate, coated in black paint or varnish.|
To preserve the ambrotype, the varnished and tinted plate was placed in a case with a decoratively pressed copper mat directly against the image. This was covered by a clear plate of glass and secured inside a velvet-lined case. These small tokens of loved ones were precious and cherished by families for generations.
Over time, climate conditions such as high humidity can break down the emulsion on an ambrotype. The image below is "burned out." The adverse effect of improper storage or poor weather conditions has caused the emulsion to pull away from the glass plate or discolor.
|Emulsion failure. Ambrotype from the collection of The National Society of The Colonial|
Dames of America in the State of Illinois, housed at Clarke House Museum.
|The Clarkes' younger daughter, Caroline, probably dressed like these girls. Ambrotype from the collection of The National Society of The Colonial Dames of America in the State of Illinois, housed at Clarke House Museum.|