Salt print

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.

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.

The most important functional difference is that it allowed a much shorter exposure to produce an invisible latent image which was then chemically developed to visibility.

Salted paper typically required at least an hour of exposure in the camera to yield a negative showing much more than objects silhouetted against the sky.

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