The daguerreotype was the first successful type of photograph. It was named after the French chemist Louis Daguerre, who announced his invention to the public at a meeting of the French Academy of Sciences in Paris in 1839. His photographic process created a highly detailed image on a sheet of copper, plated with a thin coat of silver, without the use of a negative. The process was complex. First, the silverplated copper plate had to be cleaned and polished until the surface looked like a mirror. Next, the plate was sensitized in a closed box over iodine until it took on a yellow-rose appearance. The plate, held in a lightproof holder, was then transferred to a simple camera. After exposure to light, the plate was developed over hot mercury until an image appeared. To fix the image, the plate was immersed in a special chemical and then toned with gold chloride. Exposure times for the earliest daguerreotypes ranged from 3 to 15 minutes. American photographers quickly capitalized on this new invention, and portraits based upon daguerreotypes, such as those of President Abraham Lincoln, appeared in popular periodicals and books. The popularity of the daguerreotype declined in the late 1850s when the ambrotype, a faster and less expensive photographic process, became available.