Salt print

Edinburgh Ale: James Ballantine, Dr George Bell and David Octavius Hill by Hill & Adamson, a salt print from a calotype paper negative, c. 1844
"Automatic photographic paper developed with table salt" by Alfons Mucha (1860–1939), for the Paper mill of Lancey.

The salt print was the dominant paper-based photographic process for producing positive prints (from negatives) from 1839 until approximately 1860.

Saint Michael's Church, Winterbourne, April 1859, salted-paper print, Department of Image Collections, National Gallery of Art Library, Washington, DC

The salted paper technique was created in the mid-1830s by English scientist and inventor Henry Fox Talbot. He made what he called "sensitive paper" for "photogenic drawing" by wetting a sheet of writing paper with a weak solution of ordinary table salt (sodium chloride), blotting and drying it, then brushing one side with a strong solution of silver nitrate. This produced a tenacious coating of silver chloride in an especially light-sensitive chemical condition. The paper darkened where it was exposed to light. When the darkening was judged to be sufficient, the exposure was ended and the result was stabilized by applying a strong solution of salt, which altered the chemical balance and made the paper only slightly sensitive to additional exposure. In 1839, washing with a solution of sodium thiosulfate ("hypo") was found to be the most effective way to make the results truly light-fast.

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