The daguerreotype, an early photographic process, was invented by French artist and photographer Louis-Jacques-Mandé Daguerre. Introduced in 1830, it was the first publicly available photographic process but was superseded by less complicated processes in less than fifty years.
To make the image, a daguerrotypist would follow these steps:
- polish a sheet of silver-plated copper to a mirror finish;
- treat it with fumes that made its surface light sensitive;
- expose it in a camera for as long as was judged to be necessary, which could be as little as a few seconds for brightly sunlit subjects or much longer with less intense lighting;
- make the resulting latent image on it visible by fuming it with mercury vapor;
- remove its sensitivity to light by liquid chemical treatment, rinse and dry it
- seal the easily marred result behind glass in a protective enclosure.
The image is on a mirror-like silver surface, normally kept under glass, and will appear either positive or negative, depending on the angle at which it is viewed, how it is lit and whether a light or dark background is being reflected in the metal. The darkest areas of the image are simply bare silver; lighter areas have a microscopically fine light-scattering texture. The surface is very delicate, and even the lightest wiping can permanently scuff it. Some tarnish around the edges is normal.
Several types of antique photographs, most often ambrotypes and tintypes, but sometimes even old prints on paper, are very commonly misidentified as daguerreotypes, especially if they are in the small, ornamented cases in which daguerreotypes made in the US and UK were usually housed. The name “daguerreotype” correctly refers only to one very specific image type and medium, the product of a process that was in wide use only from the early 1840s to the late 1850s.
This description adapted from information at Wikipedia.