Editing Henry Fox Talbot (section)

== The Calotype ==

{{Main|Calotype}}

[[File:Talbot Harfe.jpg|thumb|right|Horatia Feilding, half-sister of Talbot, playing the harp, c. 1842]]
[[File:David Octavius Hill.jpg|thumb|Salted paper print of [[David Octavius Hill]] from a calotype by [[Robert Adamson (photographer)|Robert Adamson]], c. 1845]]
[[File:Talbot Gravur.jpg|thumb|left|''Photoglyptic gravure'' image of plants (c. 1860)]]

The "calotype", or "talbotype",<ref>Talbot regarded the two names as interchangeable—see [https://patents.google.com/patent/US5171 U.S. Patent 5171]</ref> was a "developing out" process, Talbot's improvement of his earlier photogenic drawing process by the use of a different silver salt ([[silver iodide]] instead of silver chloride) and a developing agent ([[gallic acid]] and silver nitrate) to bring out an invisibly slight [[Latent image|"latent" image]] on the exposed paper. This reduced the required exposure time in the camera to only a minute or two for subjects in bright sunlight. The [[translucent]] calotype negative made it possible to produce as many positive prints as desired by simple [[contact print]]ing, whereas the [[daguerreotype]] was an opaque direct positive that could be reproduced only by being copied with a camera. On the other hand, the calotype, despite waxing of the negative to make the image clearer, still was not pin-sharp like the metallic daguerreotype, because the paper fibres blurred the printed image. The simpler salted paper process was normally used when making prints from calotype negatives.

Talbot announced his calotype process in 1841, and in August he licensed [[Henry Collen]], the miniature painter, as the first professional calotypist. The most celebrated practitioners of the process were [[Hill & Adamson]]. Another notable calotypist was [[Levett Landon Boscawen Ibbetson]].

In 1842, Talbot received the [[Rumford Medal]] of the Royal Society for his photographic discoveries.<ref>[https://www.bbc.co.uk/history/historic_figures/fox_talbot_william_henry.shtml BBC – History – Historic Figures: William Henry Fox Talbot (1800–1877)] [[BBC]]</ref>

In 1852, Talbot discovered that [[gelatine]] treated with [[potassium dichromate]], a sensitiser introduced by [[Mungo Ponton]] in 1839, is made less soluble by exposure to light. This later provided the basis for the important [[carbon print]]ing process and related technologies. Dichromated gelatine is still used for some laser [[holography]].

Talbot's later photographic work was concentrated on photomechanical reproduction methods. In addition to making the mass reproduction of photographic images more practical and much less expensive, rendering a photograph into ink on paper, known to be permanent on a scale of hundreds if not thousands of years, was clearly one sure way to avoid the problems with fading that had soon become apparent in early types of silver image paper prints. Talbot created the photoglyphic (or "photoglyptic") engraving process, later perfected by others as the photogravure process.
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