Manifests as: lightening of the print and/or shift in color
Primarily caused by: heat, light, and pollutants
Fade is a well-known form of image decay occurring with both traditional and digital prints. Fade is a decrease in the density of a print’s text or image due to the chemical breakdown of the printing colorants into invisible forms. Rupturing of colorant molecules can be caused by a variety of factors including heat, light (especially UV-containing light), and pollutants. For example, a print on display at room temperature is undergoing fade not only by light, but also by heat and, if present, by pollutants. The various digital printing materials have unique fade rates and different sensitivities to the various deterioration mechanisms, but in the end, fade is manifested by a decrease in overall print density or a shift in color.
Color prints are created using multiple colorants. The minimum number of colorants that can be used in modern print systems is three (cyan, magenta, and yellow), but some digital printers use up to twelve. Overall fade occurs when all of the print’s colorants fade at equal rates. The print retains its original set of hues, but is overall lighter in color. Fairly significant fade can often occur before observers find the changes objectionable, especially when a non-faded comparison is unavailable. In documents, significant amounts of fade can be tolerable and large amounts of colorant loss must occur before text is unreadable. This may be acceptable for documents of low artifactual value that are saved only for their informational content. It may not be acceptable for documents that in of themselves have historical value. Tolerance for image fade can also be variable depending on several factors including the collection type as well as the print’s value and usage.
If the print’s individual colorants fade at unequal rates (for example the magenta dye fades faster than the cyan and yellow dyes), the image will shift in hue resulting in a specific colorcast. In the example below, the magenta dye was more sensitive to light than the cyan, yellow, or black dyes. The loss of magenta caused the image to shift in color to a more greenish tint. Color shift in images is more objectionable than overall fade and even slight amounts of color shift will be considered unacceptable. Because text is usually printed with just black ink or toner, it rarely changes in color.