Fading
From The Glossary of Digital Photography
(1) Deterioration of a print or of film, which shows up gradually. Fading can be caused by exposure to light or pollutants, among other things. Sometimes the entire print fades evenly; at other times, only some colors are affected and the print develops a color cast, such that it turns orange or green. The color inks or dyes have a lifetime that is often less than that for black-and-white images. Usually photographs are best protected by storing them in the dark, where possible, or framed behind glass or ultraviolet plastic. If they are kept away from sunlight, fluorescent light, and pollutants, they will generally last longer. (2) Areas on a print that are intentionally made to gradually disappear, especially along an edge.
