Daguerreotype

This process was invented in 1839 by Frenchman Louis Jacques Mande Daguerre. It consisted of placing a sensitized silver plate in a camera, exposing it for several seconds and then developing it by fuming it with mercury. The resulting picture, a negative, was then sealed in a case to prevent tarnishing of the silver. It was essential to reflect something dark on the silver to make the picture look positive.