Ambrotypie

Ambrotypie, or ambrotype, is a positive photographic image produced on a glass plate using the wet-collodion process. Developed in the 1850s and widely used through the 1860s, it became a popular method for portraiture and small-genre subjects. The technique is similar to the collodion wet plate process, but the final image is made to appear positive by backing the transparent negative with a dark material.

In practice, a glass plate is coated with collodion, sensitized in a silver nitrate solution, and exposed in the camera while still wet. The plate yields a latent image that is developed and fixed to form a negative on the glass. To convert this into a positive, the plate is backed with a dark substance such as black lacquer, asphaltum, or a similar opaque backing. When viewed against the dark backing, the image reads as a positive photograph. The ambrotype is thus a single, viewable image on glass, easy to handle in cases and albums.

Ambrotypes offered a balance of speed, detail, and cost between the earlier daguerreotypes and later tintypes. They could be produced relatively quickly and with modest equipment, making them a staple of commercial studios and itinerant photographers of the era. The plates were fragile and required careful handling, especially the backing layer, which could deteriorate over time.

Today ambrotypes are valued as historical artifacts and for their technical and aesthetic qualities. They are collected and conserved by institutions and enthusiasts, who note their role in the evolution of mid-19th-century photography and portrait culture.