The Daguerreotype was the first publicly announced photographic process, it involves plating a copper plate with silver, buffing the plate to a mirror shine, and placing the mirrored silver plate over a box of elemental iodine. The fumes of elemental iodine react with the silver on the plate to create light sensitive silver halides. this makes the plate a sensitized film, ready for exposure. More traditional mercury development also involves fuming over elemental bromine.
Exposure and Development
After exposure, Traditionally the plate would be developed over a vacuum chamber filled with mercury, developing the latent image. In a "Becquerel development" the image is placed under a bright red safe light which develops out the image over about two hours. After development the image can be fixed and rinsed with distilled water, dried, and sealed behind a piece of glass and placed into a case.