The action of light in the sensitized plate, paper or film is just the initial stage towards the formation of the photographic image, a process that must be complemented by development. The concept, according to Newhall, was announced by Talbot in 1841. Previously, Talbot allowed the action of light to be prolonged until the image appeared. The new procedure greatly reduced the necessary exposure time.
The idea that a feeble image can be "increased, brought out, and strengthened" after the completion of the exposure process, was part of the daguerreotype process, as Talbot himself noted in an address to the British Association for the Advancement of Science, after Daguerre´s disclosure of his invention. (2) It was in fact the pioneer discovery of Niépce in the 1820s. (3)
The pictures from the Salomon Andree expedition to the North Pole in 1897 are examples of the stability of the latent image. The expedition ended with the death of the explorers. Their remains were only found in 1930. And among the materials recovered, there were photographic plates which were successfully developed 33 years after being exposed.
(1) History of Photography: From 1839 to the Present
by Beaumont Newhal, New York, 1997 (5th edition) , p. 43.
(2) History of Photography: From 1839 to the Present
by Beaumont Newhal, p.25.
(3) Photography by Eric de Maré, London, 1980, p. 20.
The Örnen (Eagle) shortly after its descent onto pack ice.
Photographs by Nils Strindberg, member of the
S. A. Andrée's Arctic balloon expedition of 1897