> Photographic processes first century

The first photographic process or heliography was invented around 1824 by Nicephore Niépce .Images were obtained with Judea bitumen spread on a silver plate after an exposure time of many days.
In 1829, Niépce associated Louis Jacques Mande Daguerre to his research .
In 1832, they put the last touch , using a residue of lavender oil distillation , a second process producing images in a one day exposure time.


In 1833 Niépce died, Daguerre went on working alone and invented, in 1838, the daguerreotype, the first process including a development stage. A silver plate coated with a very thin silver iodide layer was exposed in a camera obscura then exposed to mercury vapors that induced the apparition of the invisible latent image that had been formed during the exposure to light. This development was in fact such an amplification of the effect of light that the exposure time was hardly more than 30 minutes. Fixing was done by immersing the plate in sea salted water.




In July 1839, another frenchman, Hippolyte Bayard, discovered the way to obtain positive images directly on paper. A sheet of paper covered with silver chloride was blackened by light then exposed in a camera obscura after being sensitized in silver iodide.
The exposure time was from 30 minutes to 2 hours .





Hyppolite Bayard

Henry Fox Talbot
Still in 1839 , the announcement of the daguerreotype invention incited an englishman, William Henry Fox Talbot, to resume interrupted research, the beginning of which was in 1834. In 1841, he patented the calotype, the first negative-positive process that made it possible to multiply the same image because of an intermediate negative on a silver chloride paper made translucid with wax . As for the daguerreotype, the latent image was developed by a chemical agent , the developer : a solution of gallic acid and silver nitate. A second sheet of paper also covered with silver chloride was then exposed through the translucid negative, to give the final positive .





John Herschell

We owe to John Herschell the discovery, in 1839, of the way to fix images by dipping them in a sodium hyposulfite bath that is still used today as the main component of photographic fix-baths. The main advantages of the calotype were the easiness with which one could manipulate the paper prints and the possibility of multi-ptinting. On the other hand, the sharpness, limited by the fibers in the negative paper , could not compete with the daguerreotype .




To reduce further the exposure time , short focal lenses were created , letting more light in the camera , however keeping the sharpness on the whole image . In 1841 , the physicist Fizeau replaced silver iodide by silver bromide, the sensibility of which to light was far superior . Time exposures of barely a few seconds were needed to obtain a daguerreotype and so it became possible to do portraits.

To improve the calotype negative transparency, Abel Niépce de Saint-Victor had the idea in 1847 to replace paper with glass. So that the silver bromide might adhere to glass, he had the idea to mix it with albumen (egg whit ). Even though a bit too contrasty, images then became extremely sharpen, forcing opticians to work on higher definition lenses.




In 1851, an Englishman named Scott Archer replaced albumen by collodion, the base of which is gun-cotton (cellulose nitrate ). The black and white images with process reached a quality unknown until then; The only drawbacks were that the picture had to be taken while the collodion on the plate was still humid and the developement immediatly after the exposure.








Scott Archer