Light-Induced and Thermally-Induced Yellowish Stain Formation in Inkjet Prints and Traditional Chromogenic Color Photographs

Inkjet printing of photographs using both dye-based and pigmented inks has become the most popular form of hardcopy output from digital camera files. In addition to desktop and wide-format applications, inkjet printing technology is now also being adopted for “dry” minilabs and by professional portrait and wedding photography studios. Various factors affecting both light-induced and thermally-induced yellowish stain formation in inkjet prints are described. Stain behavior for representative inkjet papers as well as for selected traditional chromogenic color prints are discussed. Using data obtained from high-intensity 35 klux tests and with long-term 1.0 klux tests, potential stain formation and optical brightener activity loss reciprocity failures are described. Problems with the integration of lightinduced and thermally-induced yellowing data in accelerated image stability tests are also discussed. * 713 State Street, Grinnell, Iowa 50112 U.S.A. Introduction Color photography has had a very long history of problems with gradual yellowish stain formation that has occurred both with prints stored in the dark and when exposed to light on long-term display. Kodacolor, introduced by Eastman Kodak in 1942, was the first mass market chromogenic color negative film and color print process and was the historical predecessor of today’s chromogenic color film and print materials. With prints made for more than a decade after its introduction, Kodacolor prints suffered from severe thermally-induced yellowish stain that developed gradually during storage. Some examples studied by this author now have d-min blue densities of above 1.0. These Kodacolor prints also had very poor light stability and, with no known examples of prints still surviving in reasonable condition, that period of color photography has been referred to as “The Totally Lost Kodacolor Era of 1942– 1953.” The primary cause of the yellowish stain that occurred in dark storage has been attributed to the presence of non-reacted magenta coupler remaining in the prints at the completion of processing and washing. Over time, these residual couplers can develop significant stain levels. Improvements were made by Kodak in 1954–55, but magenta coupler-produced-stain continued to be a problem for chromogenic prints. As shown in Figures 1 and 2, further complicating the matter is the fact that rates of yellowish stain formation may significantly increase when prints are stored in the dark after exposure to light during display.1 The first “low thermal stain” color negative paper was introduced by Fuji in 1985 under the Fujicolor Paper Type 12 name. Further improvements were made by both Fuji and Konica and in the early 1990’s both companies introduced further improved products. Kodak’s first “low thermal stain” color negative papers, Ektacolor Edge 7 and Portra III, were introduced in the mid-1990’s. With the advent of digital minilabs introduced in recent years by Fuji, Agfa, Konica, Noritsu, and other companies, chromogenic color papers such as Fujicolor Crystal Archive and Kodak Generations are now extensively used for printing digital camera files.