The problems of the paper negative became academic in October 1847 when Abel Niepce de Saint-Victor, an army officer and cousin of Nicephore Niepce, appeared before the Academy of Sciences in Paris to announce his new process, one that used glass plates coated with an emulsion of a silver compound suspended in egg white. The advantages of glass over paper as a base had been apparent for some time to other experimenters; glass preŽsented no texture problems, was uniformly transparent and chemically inert. But until Niepce de Saint-Victor used egg white, no one had found an emulsion that would hold a light-sensitive material on glass, although many sticky substances, including the slime exuded by snails, had been tried.
To prepare his emulsion, Niepce de Saint-Victor functioned as part chef and part chemist. To the egg white he added a bit of potassium iodide and the whipped the mixture until it was stiff. This froth was spread evenly on the glass plate, permitted to dry and was then made light sensitive by being dipped into a bath of acidified silver nitrate.
Black and white photographers were not unanimously enthusiastic about the new process, however. Although it could produce black and white pictures with excellent detail, thanks to the textureless base, the early egg-white plate was easily damaged and was no faster than the calotype; black and white image quality varied with the relative freshness of the eggs; and the plates were heavy, clumsy to manipulate and fragile. But the demonstration of the practicality of glass as a base was to prove of enormous importance to black and white photography. With the discovery of a far better emulsion a few years later, black and white photographers quickly learned to live with the inconveniences and shortcomings of glass plates.
Probably nothing could have been more remote than black and white photography in the mind of Louis Menard, a French chemist, when he discovered in 1846 that guncotton (cellulose nitrate) would dissolve in a mixture of ether and alcohol to produce a highly viscous liquid that dried into a hard, colorless, transparent black and white film. He called the substance "collodion." He could find no use for this odd fluid but physicians soon adopted it as a dressing for minor wounds. Applied as a liquid, collodion dried into a tough, waterproof covering that protected the damaged area and kept it clean. The idea of using collodion as a black and white photographic emulsion was first advanced by Robert Bingham, a British chemist, in January 1850.
Coating a plate required nimble fingers, flexible wrists and practiced timing. After pouring collodion in the middle of the plate, the black and white photographer held the glass on the edges with his fingertips and tilted it back and forth and from side to side until the surface was evenly covered. The excess collodion was poured back into its container. After being sensitized in silver nitrate, the plate was exposed while still damp and then developed immediately, for Bingham had learned that the collodion emulsion became less sensitive as it dried. Thus the process became known as "wet-plate black and white photography."
When wet collodion plates were developed in pyrogallic acid (pyrogallol), introduced in 1851, exposure time could be reduced to as little as five seconds. Because this high speed permitted the taking of black and white pictures never before possible, black and white photographers were willing to put up with the tedious business of preparing the plates and the need to complete the exposure-to-development cycle while the emulsion was still wet. It was with cumbersome wet plates that Mathew Brady and his men documented the Civil War and William Henry Jackson black and white photographed the American West.