The daguerreotype was the first commercially viable photographic process. Invented in 1839, it is unique in that it is based on the light sensitivity of pure silver metal to the halogen elements iodine, bromine, and chlorine. Other silver based photographic processes require the combination of silver ion in solution with a halide (iodide, bromide, and chloride) also in solution. 

The daguerreotype bears the name of its inventor, Louis Jacque Mandé Daguerre. Daguerre and Nicéphore Niépce began a formal partnership in 1829. They were introduced three years earlier by Charles Chevalier, an optician from whom they both bought lenses for their cameras. Niépce had already produced images with the camera obscura using his heliography process, while Daguerre was exploring ways to permanently fix the image produced by the camera. Niécpe died in 1833 and Daguerre continued their research, producing his first images in 1835 and his first “fixed,” or rather stabilized, images in 1837. 

After failed attempts to market and sell the process, Daguerre found government support through François Arago, a scientist and member of the French legislature. The process was introduced before a joint session of the Académie des Sciences (Academy of Sciences) and the Académie des Beaux-Arts (Academy of Fine Arts) in August 1839. Daguerre’s invention was bought by the French government, Daguerre was given a lifetime pension, and the process was given freely to the world (except England where it was patented). An entire industry was built around photography with the first cameras manufactured by Giroux and the first lenses by Charles Chevalier.

To make a daguerreotype, a sheet of silver plated copper was polished until the silver had a mirrored surface. The silver was first polished in a circular motion using cotton flannel with a rotten stone and alcohol slurry. It was then buffed with rouge to give the plate a fine polish and remove the circular marks. The buffing apparatus could be a wheel or paddle consisting of a wooden handle, several layers of cotton flannel for padding, and covered with velvet or soft buckskin. The buffing was always done in the opposite direction of the intended view. For example, for a vertical portrait, the buffing was done horizontally. Daguerre’s original instructions called for sensitization with fumes of iodine crystals, exposure in the camera, “development” over heated mercury, and then fixing in a hot saturated salt (sodium chloride) solution. There were several subsequent improvements to the process which increased the stability, light sensitivity, and overall contrast and appearance of the image. 

The salt solution stabilized the image, but did not remove the residual light sensitive silver halides. One of the first improvements, suggested by John Herschel, was fixing in sodium thiosulfate which completely removed light sensitive compounds. A cyanide fixer was also occasionally used. In 1840 Hippolyte Fizeau introduced gilding in which the image was treated after fixing with a solution of gold chloride and sodium thiosulfate, slightly heated. This increased contrast and brilliance of the image and also made the image particles better adhere to the silver surface of the plate. The image particles of un-gilded daguerreotypes are very delicate and can easily be wiped from the surface of the plate. Several practitioners discovered that light sensitivity could be increased by sensitizing the polished plate to iodine and bromine or chlorine. The halogens were relatively newly discovered elements and were both difficult to handle and to obtain. However, the use of bromine especially increased sensitivity significantly and became standard practice by 1842. The common sensitization procedure was to expose the plate to iodine fumes until the plate was yellow, then to bromine until the plate was a rose color, then briefly back over the iodine fumes. Beginning in the mid-1840s practitioners electroplated additional silver onto the plates after polishing in a process called galvanizing—this was particularly popular in the United States. Technological improvements included significantly better lenses, namely the Petzval lens, better cameras, and studio lighting techniques which directed more light into the studio. 

While Daguerre’s original specifications required exposure times of up to thirty minutes, these chemical and technological improvements reduced exposure times to several seconds making portraiture a possibility. Portrait studios sprang up world wide, though primarily in Europe and the United States. The daguerreotype is known for it’s highly reflective surface, jewel-like appearance, and extremely high resolution. This process is capable of capturing more detail than any subsequent photographic process to date. The underlying chemistry and physics of the process were a mystery to Daguerre and his contemporaries and largely remain a mystery today. There has been significant research into both the physical and chemical nature of the process and several theories have emerged related to image formation, the effects of gilding, and mechanisms of deterioration.