daguerreotype

The daguerreotype is an early photographic process that produces a highly detailed positive image on a polished silver-plated copper sheet. It was publicly introduced in 1839 by Louis Daguerre, who developed the method building on work by Nicéphore Niépce. The procedure was widely adopted in the 1840s and 1850s and played a key role in popularizing photography; unlike later processes, a daguerreotype yields a single, non-reproducible image.

In brief, the plate is polished, sensitized with iodine to form silver iodide, then placed in a camera and exposed to light. After exposure, the latent image is developed by exposing the plate to mercuric vapor, which binds with the exposed silver to reveal the image. The result is then fixed by washing in a fixing bath, usually a solution of sodium thiosulfate or, in earlier practice, common salt, to remove unexposed silver iodide. The plate is rinsed, dried, and often toned with gold to enhance contrast. Exposures were long in the early days and gradually shortened with improvements in chemistry and optics. The finished daguerreotype is a unique positive image with a mirror-like surface.

Daguerreotypes were especially popular for portraiture and urban scenes, and studios flourished worldwide. They require careful handling due to the toxicity of mercury used in development, and the images are fragile; copies could only be made by re-photographing or creating a new daguerreotype from the scene. By the 1850s, processes based on negative glass or paper supports offered easier replication, and the daguerreotype gradually declined in favor of these and other methods.