APPLICATIONS PRINTING IN BLACK & WHITE PRINTING TECHNIQUES
Salt printing is an old process technique whereby paper is treated with a solution of salt and silver nitrate and then subjected to outdoor exposure (sunlight).
The resulting salt process ‘sun picture’ is characteristic for its matt appearance, and reddish brown colouring.
Salt prints were made until about 1860, although in decreasing numbers after the advent of the albumen print in 1851. A finished salt print is matt in tone, reddish brown in colour, and has no surface gloss. Its highlights are usually white (Note too - if toned, it will be purplish brown, and if faded - it will be yellowish brown).
The traditional method involves making sun pictures or photogenic drawings.
For in depth details on how to achieve salt printed images - it would be advisable to visit appropriate web sites on the subject (there are several - which detail the process involved, as well as giving historical accounts of the effect).
However, in brief the process involved in making a salt print is:-
- A sheet of paper is soaked / sensitised with a solution of salt (sodium chloride), followed by coating one side only with silver nitrate. (This produces light-sensitive silver chloride in the paper).
- After the coated paper is dry, it is placed sensitive side up - directly under a negative and beneath a sheet of glass within a printing frame.
- This paper negative / glass sandwich is then contact printed - by exposing it glass side up, outdoors in the sunlight.
- The exposure time (up to approx two hours) needs to be determined by visual inspection.
- When the print has achieved its desired intensity, it is removed from the frame and fixed with sodium thiosulphate (or hypo) - to halt the chemical reaction.
- The image is then thoroughly washed and dried.
In order to achieve better permanence, prints can be toned with gold chloride. This will also enhance the tone and give richer results.