Ambrotype of a woman holding a book, wearing a gold-rimmed ring on her left ring finger. On the back, a studio label reads "Artist Photographer Guche Fossé de l'intendance, Bordeaux." The photographer was based at this address from 1861 to 1868.
 Patented in 1854 by James Ambrose Cutting, an ambrotype is a negative on a glass plate, which, when viewed in transparency, becomes a positive when placed in front of a black background.
 
 The ambrotype was commonly used from 1854 until the 1870s. Less expensive and requiring a much faster exposure time than the daguerreotype, it was widely used by portrait photographers. To obtain the negative of this unique image, a previously cleaned glass plate was coated with a layer of collodion. After drying, a transparent varnish was applied, sometimes with touches of color. Presented on a background of fabric or black paper, it was delivered in a union case or frame, as with daguerreotypes, which often leads to confusion in identifying these two processes.