Fabric Fading in Sunlight
What causes fabric to fade when it is put out in the sunlight?
Though at first one would not think so, sunlight is pretty energetic. Look how it
causes skin to tan and plastics to break down. Likewise, when exposed to sunlight,
many kinds of molecules that give a fabric its color can be broken into smaller pieces
that are either colorless, or at least different in color than the original dye. In
fact, most common dyes will fade if exposed to light for a long enough time. About
the only colored substances that resist fading are made of solid pigments similar to
those used in permanent inks and/or artists' oil paints.
Fabrics are colored because of the dyes and/or pigments formulated into the fabric, or
the threads from which the fabric is woven. Dyes get their color frequently because
there is an extended number of carbon-to-carbon double bonds or carbon rings. In
sunlight, especially the ultraviolet part that has a wavelength just shorter than about
400 nanometers the dye not only absorbs the light but undergoes a chemical reaction.
If the product of that reaction is not colored, or has a different color than the
reactant, the fabric will either fade (lose color) or change color. You can see this
very rapidly if you spread a film of regular mustard and cover one part with
an opaque cover -- for example aluminum foil -- and the other with a transparent cover
such as glass within a few hours you will see the mustard exposed to sunlight (or even
fluorescent light) fade and the part covered by the opaque sheet remains its original
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Update: June 2012