The term cased photograph refers specifically to two 19th century photographic media: the daguerreotype and the ambrotype, and, slightly less accurately, the tintype.
The earliest and most important of these processes, the daguerreotype, consisted of a photographic image on a highly polished silver-coated copper plate. The emulsion, the layer of light sensitive chemistry that recorded the image, was fragile and prone to damage by abrasion. Because of the delicate nature of the photo surface, daguerreotype plates were always covered by glass and, typically, kept in a hinged case.
In the ambrotype, a cheaper alternative to the daguerreotype, the image was an underexposed and underdeveloped negative on a glass plate. In order to be viewed as a positive image, the plate had to be backed by a dark surface to allow for light reflecting back through the glass to invert the tonality of the image. To protect the glass base for the negative, the ambrotype was usually kept in the same types of cases used for daguerreotypes.
The tintype is essentially the same process as the ambrotype, except that the underexposed negative image is based on a piece of black lacquered iron or steel (the process is more accurately called a ferrotype as no tin is used). While it was not critical for the tintype to be kept in a case, and they were often sold without them, they were cased often enough to be classified with the other cased photographs.
In addition to the big three mentioned above, we have included under the designation of cased photographs: all photographs in the collection with a non-paper base and also paper photographs kept in cases for presentation.
Plate sizes: The typical plate sizes for daguerreotypes are based on the fractional proportions of the whole plate which measured 6 ½” x 8 ½”. The ambrotype and tintype adopted the same dimensions. Although the images were usually priced and sold by the plate size, the sizes were not perfectly standard and there is often quite a bit of variation in the exact size. And although they are fairly rare, there are cased photographs produced at larger than whole plate size.
Cases: Most of the Boston Public Library’s cased photographs are in embossed leather cases, sometimes with a brass mat between plate and glass. One image is in a highly decorative “union case” an early thermoplastic process. Several of the whole plate daguerreotypes are framed, although they may have been removed from their original cases sometime in the 19th century.
Special thanks to Chris Steele for his work in identifying and describing the cased photograph collection at the Boston Public Library.
For more information please contact:
McKim Building, 3rd Floor
Boston Public Library
700 Boylston Street
Boston, MA 02116
617-859-2280 or 617-536-5400