Examples of Gelatin POPs
Warm image tone, reddish-brown to purple-brown
Image discoloration and fading common
Glossy surface
Thick baryta layer, paper fibers obscured
Common Use Dates: 1885-1910
Alternate Names: Gelatin silver chloride print, Gelatin Chloride POP, Aristotype
Mistaken For: Collodion POP, Albumen Print
Process Family(s): Photographic, Silver, Gelatin Binder, Printing-out, Print
Gelatin printing-out prints are based on the light sensitivity of silver chloride, which is suspended in a gelatin binder on a baryta paper support. While recipes for making gelatin printing-out papers were available, high grade gelatin was needed. It was much more common for practitioners to purchase commercially made gelatin photographic papers. One recipe for commercially manufactured paper requires mixing a solution of silver nitrate, citric acid and distilled water with a solution of hard gelatin, sodium chloride, potassium citrate, and water. After these two solutions were combined, alcohol and alum (a hardener) were added. This emulsion is then coated onto baryta paper. Like all printing out papers, there is an excess of silver nitrate.
Printing-out papers were contact printed under ultra-violet (sun) light. The print was then washed, gold toned with a gold chloride solution, washed again, placed in a stop bath to stop the toning action, fixed with “hypo” (sodium thiosulfate), washed again, and dried. Prints were usually placed in a hardening bath of alum and “hypo” between the toning and fixing baths. Alternatively, prints could be placed in a combination bath containing both gold and hypo, so they would be toned and fixed simultaneously. Self-toning papers had gold salts incorporated, so no toning step was needed. Prints were then usually trimmed and mounted. During the mounting process, prints could be burnished to obtain a glossy surface.
Gelatin printing-out papers were invented by Sir William Abney in 1882 and were commercialized by several companies beginning in 1884. By the late 1890s gelatin POP out sold collodion POP, but was displaced by gelatin developing-out papers in the 1910s and 1920s. Gelatin printing-out papers continued to have a niche market, first as studio proof paper and later used by fine art photographers and continued to be manufactured until late 2000s.