Many factors contribute to the fading of images, which includes original paintings, photographic materials and inkjet prints. The principal ones are light intensity and brightness, radiation (particularly ultraviolet), relative humidity, and chemical constituents in the ambient atmosphere. Traditionally in the art world, the Blue Wool Test has been used as a hallmark, but this does not include any assessment of the effect of humidity, now shown to be significant by the scientific testing of digital inkjet technology.

It is common for someone producing prints for sale to state a "longevity" rating, indicating that the print will last for so many years without fading. This can often be a very misleading misquote from an ink or paper manufacturer's statements. Even independent scientific testing, which is far more reliable, is rarely up to date with the rapidly-evolving technologies of inks, pigments and paper coatings.

As always, what do these terms mean? All pigments fade. Van Gogh's White Roses were originally bright red! The best known scientific tests done at www.wilhelm-imaging.com use 30% as a standard. The question is, at what point does fading become perceptible for the average person? Even within one work, this will vary both with the actual colour, and the depth of colour. Thin watercolour fading will be more apparent than with thick oil paint. Fading becomes perceptible much earlier if we are making a side-by-side comparison with how it was originally, but observation is rarely done under these conditions.

The subject is so complex, it is impossible to compare ratings based on test information. Manufacturer's measurements vary widely, so that a print rated at 25 years could be far more fade-proof than one rated at 65 years. Kodak for instance use a light brightess only a quarter as bright as Epson in their tests (120 lumens/watt compared to 450 lumens/watt), extending their longevity rating considerably.  The problem with independent scientific testing is that it only tests one specific combination of printer, ink and/or pigment, media (paper), and receiver coating (the layer the ink sits in or on), whereas out in the market the permutations of these factors runs into thousands.

Some manufacturer's claims are a form of hybid testing, where they have their product tested independently, but specify the actual test conditions. We know of only one example where independent testing is commissioned to more stringent than normal conditions. These are the Jon Cone Piezography pigments, measured in conditions of varying humidity of 20-90%, compared to the usual unvarying test condition of 50%.

Tony Riley

Last revised Jan 2007