NEGATIVE TO POSITIVE PROCESS
The inventor of the first negative from which multiple positive prints were made was Henry Fox Talbot, an English botanist, mathematician and a contemporary of Daguerre.
Talbot sensitized paper to light using a silver salt solution. He then exposed the paper to light. The background became black and the subject was rendered in gradations of grey. This was a negative image. And from the paper negative, Talbot made contact prints, reversing the light and shadows to create a detailed picture. In 1841, he perfected this paper-negative process and called it a calotype, Greek for beautiful picture.
Tintypes, patented in 1856 by Hamilton Smith, was another medium that heralded the birth of photography. A thin sheet of iron was used to provide a base for light-sensitive material, yielding a positive image.
WET PLATE NEGATIVES
In 1851, Frederick Scoff Archer, an English sculptor, invented the wet plate negative. Using a viscous solution of collodion, he coated glass with light-sensitive silver salts.
Because it was glass and not paper, this wet plate created a more stable and detailed negative.
Photography advanced considerably once sensitized materials could be coated on plate glass. However, wet plates had to be developed quickly before the emulsion dried. In the field, this meant carrying along a portable darkroom.
DRY PLATE NEGATIVES & HAND-HELD CAMERAS
In 1879, the dry plate was invented, a glass negative plate with a dried gelatin emulsion. Dry plates could be stored for a period of time. This meant photographers no longer needed portable darkrooms and could now hire technicians to develop their photographs. Dry processes absorbed light so rapidly that the hand-held camera was now possible.
FLEXIBLE ROLL FILM
In 1889, George Eastman invented film with a base that was flexible, unbreakable and could be rolled. Emulsions coated on a cellulose nitrate film base, such as Eastman’s, made the mass-produced box camera a reality.
In the early 1940s, commercially viable color films (except Kodachrome) were brought to the market. These films used the modern technology of dye-coupled colors in which a chemical process connects the three dye layers together to create an apparent color image.