Daguerreotypy was the first widely used photographic process. The pictures consist of silver mercury amalgam particles on a silver substrate. An explanation of the process has been developed, since this was not available in the literature. The results of a detailed electron microprobe analysis of daguerreotypes in good condition indicate the plates to be about 0.4 millimeters thick; comprised of a thin silver layer averaging 4 mum thickness on a copper backing. The silver layer contained about 2 per cent copper by weight. Mercury was not found except within image particles. Gold was observed everywhere on the surface in a thin layer (0.75mum). Deteriorated daguerreotypes were also examined and the deterioration products classified. Smooth films characterized by interference colors were determined to be largely silver sulfide. Silver sulfide was additionally found as crystalline particles. Copper formed the major constit-uent of another type of deterioration film. Copper was also found in green accretions, often associated with the presence of sodium and calcium. Sodium and calcium were found as deterioration products of the glasses covering these plates. Our studies have shown that interdependent deterioration processes are present, involving the plate surface, the copper support, the cover glass and the microclimate in the case around the plate.