The salt printing process belongs to the printing-out paper (POP) process. POP means that the image appears during exposure, the progress of exposure may be checked visually and stopped at the right moment. It also has a very long tonal range, and can reproduce detail from negatives of greater density range.
The process begins by sizing the acid free high quality paper such as the Arches Platine Paper with a mixture of gelatin , sea salt (sodium chloride) and water. Once dried, a 12% silver nitrate solution is brushed onto the surface in a dim room. The silver nitrate will react with the sea salt to form silver chloride which is light sensitive.
The paper is then contact printed with a negative using sunlight or UV light. The timing may differs but generally the print has to be darker by 2-3 stops as the toning and fixing process will lighten the prints. A good way to know the exposure is enough is when it becomes difficult to see the image, because of the darks of the negative (where the sun is not shining through as much) and the darks on the paper (where the sun hit and the final image will be dark). It is then wash for a minute using tap water and gold toned. Finally it is fixed for about 4 minutes using the hypo fixer . The final rinse will be abotu 30 minutes to clear all the unused fixer.