Apr 15, 2011
After producing yet another disappointing image one day, Daguerre tossed the silverized plate in his chemical cabinet, intending to clean it off later. But when he went back a few days later, the image had darkened to the point where it was perfectly visible. Daguerre realized that one of the chemicals in the cabinet had somehow reacted with the silver iodide, but he had no way of know which one it was. Below is him in a colorized daguerreotype.
For weeks, Daguerre took one chemical out of the cabinet every day and put it in with a newly exposed plate. But every day, he found a less-than-satisfactory image. Finally, as he was testing the last chemical, he got the idea to put the plate in the now-empty cabinet, as he had done the first time. Sure enough, the image on the plate darkened. Daguerre carefully examined the shelves of the cabinet and found what he was looking for. Weeks earlier, a thermometer in the cabinet had broken and left a few drops of mercury on the shelf. it was the mercury vapor interacting with the silver iodide that produced the darker image. Daguerre incorporated mercury vapor into his process, and the Daguerreotype photograph was born.