Photograph courtesy of Cameras From Daguerreotypes to
Instant Pictures by Brian Coe
In 1837 Loius Jaques Mandre Daguerre developed a process based on the
exposure of a highly polished silver surface to Iodine vapor which produced
on it a layer of light sensitive silver iodide.
An exposure of twenty minutes or more in the camera obscura produced
no visible change on the plate but by then exposing it to the vapor from
heated mercury an image was developed by the amalgamation of the mercury
vapor with the tiny specs of silver produced by the light action. The plate
was fixed by washing it in a very strong solution of common salt (Sodium
Daugerre announced his discovery on the 7th of January 1839 and the
working details were published in August 1839.
This "Daguerreotype" process was
a positive only process and was a once only process.
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