Kalo type or number botype

"Kalotype", or "talbotype" was a developing process, developed from Henry Fox Talbot's previous image-developing process by using a different silver salt (silver iodide instead of silver chloride) and a developing agent (bile acid and silver nitrate) to produce an invisibly light "latent" image on the exposed paper. This reduced the exposure time in the camera to just a minute or two for subjects in bright sunlight.

The transparent negative kalotype made it possible to produce as many positive pressures as desired by simple contact pressure, while the daguerreotype was an opaque direct positive that could only be repeated by being copied with a camera. On the other hand, although the negatives were waxed to make the picture clearer, the kalo type was not as razor sharp as the metallic daguerreo type because the paper fibres blurred the printed image. The simple salt paper process was normally used when making prints from kalotype negatives. Talbot announced his kalotype process in 1841. In August, the first photographer was licensed to use the method.

In 1852, Talbot discovered that gelatin treated with potassium dichromate, a sensitizer introduced by Mungo Ponton in 1839, becomes less soluble when exposed to light. This later formed the basis of the important carbon pressure process and similar technologies. Dicromerad gelatinis tint is still used for some laser holography.


Britannica: Calotype[WWW 2020-04-04]
Wikipedia: Henry Fox Talbot[WWW 2020-04-04]

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