daguerréotype

Daguerréotype is an early photographic process developed in the 1830s by Louis Daguerre in France. It yields a direct positive image on a highly polished silver-plated copper plate. Because the image forms directly on the plate and there is no negative, each daguerréotype is unique; duplicates require re-exposure or copying the image by contact or rephotography.

Process: The plate is polished to a mirror finish and sensitized by exposure to iodine vapor to form silver iodide on its surface. After being placed in a camera and exposed to light, the latent image is developed by exposing the plate to mercury vapor, which amalgamates with silver to create a visible image. The image is fixed by bathing the plate in a solution of sodium thiosulfate (hypo), washed, and dried. Optional gilding (a thin gold layer) can improve appearance and durability. Many daguerréotypes were subsequently sealed behind glass in a protective case.

History and impact: Publicly announced in 1839, the daguerréotype offered extraordinary detail and was quickly adopted for portraiture and urban scenes, becoming the dominant photographic process in the 1840s and early 1850s. It remained popular for a time but required careful handling and was difficult to produce in large quantities. By the 1850s and 1860s, lighter negative-based processes such as the collodion process and albumen prints largely supplanted it.

Preservation: Surviving daguerréotypes are sensitive to light, air, and handling and are commonly kept in protective cases with glass to prevent contact with the image.