SALTED PAPER
William Henry Fox Talbot's original salted silver nitrate paper evolved between 1834 and 1839. Talbot used smooth writing paper washed in a weak solution of common salt, dried, then coated with a solution of silver nitrate, resulting in light-sensitive silver chloride. Once dry, the paper could be printed out in strong sunlight. The resulting image of metallic silver was fixed in a strong solution of salt. Talbot refined the process, and Sir John Herschel suggested sodium thiosulphate (hypo) as a fixing agent. Salted paper was the basis for Talbot's Calotype process, which used silver nitrate and gallic acid to develop up a latent image in the exposed paper, and is the foundation of modern silver-based photography.

The Process
Paper: good quality art paper. Note: rinse utensils, etc. with distilled water before use.

Salting solution
1.8% solution Sodium Chloride (1.8g to 100ml. purified water) Salt the paper by soaking in the salting solution for about 2 minutes. Be sure to disperse any air bubbles that may form on the surface. Blot with photographic blotting paper, and allow to dry.

Sensitising solution
3g silver nitrate to 20ml. distilled water 20% solution Citric Acid (saturated solution, 2g to 10ml distilled water)
Mix 3ml Silver Nitrate to 0.3ml Citric Acid - just before coating. Sensitise the paper in subdued tungsten light (see 'Coating methods').
Dry paper in the dark, then re-humidify over bath of washing soda or plain water.

Printing
Contact print by inspection in sunlight or under an ultra-violet lamp, until the image is 1/2 stop over-exposed.
Wash the print in running water until the milky silver compound has completely dispersed (2-20 minutes, depending on paper weight.

Fixing
Fix the print in a plain sodium thiosulphate fixer for 5-30 minutes (depending on the paper, as above). Wash in running water for 15 to 30 minutes, depending on the paper weight.

KALLITYPE PROCESS
This is an iron-silver process. In 1842 Sir John Herschel invented the chryso-type process, using a strong solution of ferric ammonium citrate as a light-sensitive coating on paper. Once exposed, the paper was developed up with silver nitrate (Herschel first used gold chloride), washed, and fixed in hypo (another of Herschel's many innovations). The latterly termed Argerotype process was not much used, but in 1889, W. J. Nicol based his Kallitype process on Herschel's work. Known as the 'poor mans platinum', the Kallitype had many complex and sometimes highly toxic variations. In its most basic (and least toxic) form, a light sensitive coating of ferric ammonium citrate and silver nitrate produces a sepia image of great richness.

The Process

Sensitiser
Note: Rinse all utensils in distilled water before use.
Make 3 separate solutions;
6g Ammonium Ferric Citrate in 22ml distilled water
1g Tartaric Acid in 22ml distilled water
2.50g Silver Nitrate in 22ml distilled water

The tartaric acid should be freshly mixed just before combining the solutions to sensitise. The other solutions will keep in brown bottles, away from light. The ammonium ferric citrate solution may need to be filtered before use.
Mix the first two solutions. Add the silver nitrate slowly, a few drops at a time, stirring well to be sure that there is no milky precipitate.
Paper: Use a good quality art paper.
Sensitise the paper by coating (see 'Cyanotype' for suggestions) in subdued tungsten light. Dry in the dark.

Printing
Expose in sunlight or by ultra-violet lamp in contact under a negative until the image prints out. Do not overprint: the image will intensify during fixing. Wash in running water until all milky silver nitrate residue disappears.

Fixing
12g sodium thiosulphate in 1 litre water
Fix until image reaches maximum density: beware of over-fixing, which will erode the image.Wash thoroughly in running water (up to 30 minutes if thick paper is used).
Note: Iron-silver prints may be toned with gold toner as per (Talbot's) salted paper.