The silver gelatin-bromide

In 1822, Nicéphore Niepce, a Frenchman, obtained what is widely regarded as the first photograph: an image which required an exposure time of eight hours printed on a glass plate rubbed on with a layer of bitumen of Judea.

The painter, Louis Jacques Mandé Daguerre, who was associated with Niepce, improved the process and obtained images by using silver iodide on a copper plate in 1834. Eventually the exposure time is reduced to minutes. It is a non reproducible direct positive called the "daguerreotype". The discovery was officially announced by the Academy of Sciences in Paris on July 7, 1939.

At the same time, in England, William Henry Fox Talbot announced the discovery of the "Calotype", a negative process, on a paper soaked with a solution of silver iodide. This process allowed the unlimited reproduction of the image: it is the direct precursor to the current silver-based photography using negatives and positives (prints).

Since 1840, there have been many rapid improvements, including the decrease of the exposure time, the use of glass as support for the photographic emulsion, gelatin being replaced by albumin in 1847 then by wet collodion in 1851. Finally in 1871 the Englishman Richard L Maddox replaces collodion by a mixture of gelatin and cadmium bromide sensitized with silver nitrate then dried on a glass plate. With a much higher sensitivity, this emulsion allowed instantaneous photography. Then, at last, contrary to the collodion which was to be used wet and thus prepared on the spot, the plates with silver gelatin-bromide were invented, which could be prepared in advance thus avoiding to carry the heavy and cumbersome laboratory material.

In a short time, an industry of "dry plates" and films will develop in the Lumière factories of Lyon-Monplaisir (which is also the origin of the cinema).

Though improvements were made throughout the 20th century, the silver-gelatin emulsion is still used for traditional black and white photography.