The Effect of Light on Dye
It is one of nature's inevitabilities that all colored objects constructed from organic materials will fade upon exposure to light. Lightfastness is the degree to which a dye resists fading due to light exposure. Scientists writing in the Textile Research Journal found that the lightfastness of dye depends on the location of the dye in the fabric and also upon the dyeing conditions.
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History
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The first rigorous testing of the lightfastness of dye was made by Charles François de Cisternay DuFay, a French scientist and superintendent of the Jardin du Roi of Paris in 1733. The dyes tested by DuFay were from natural sources and are today almost all obsolete. Scientists writing in Studies in Conservation found that nearly all natural dyes will serious fade in less than half a century.
Damaging Light
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What humans commonly refer to as "light" is the portion of the electromagnetic spectrum that is visible to their eyes. This includes wavelengths of between 390 and 750 nanometers. Shorter wavelengths of between 300 and 400 nanometers are not visible to the human eye and are commonly known as ultraviolet light. Because these shorter wavelengths are more photo-chemically reactive, they are more damaging to dye. Daylight contains the greatest percentage of damaging ultraviolet light.
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Individual Differences
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Different dyes demonstrate varying degrees of resistance to the fading caused by light. However, all dyes have some susceptibility to light damage because of the way color works. Dyes which result in a bold, strong color do so because they absorb all of the wavelengths that aren't reflected back. It is this absorption that does the damage.
Types of Dye
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Vat dyes are the most lightfast type of dye, with reactive and acid dyes a little less so. Direct dyes don't generally score highly in terms of their lightfastness, but there are a few notable exceptions. The dyes most likely to fade are the basic dyes. Although they possess the most striking colors, they are unfortunately highly sensitive to light; especially when used with natural fibers. They keep their color longer when used with synthetic fibers.
Reducing Damage
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To ensure dye keeps its color for as long as possible, keep it out of daylight as much as possible. Try drying clothes inside and keeping them in the dark when they're not being worn. Dye on objects not in use can be preserved to some extent by keeping it away from oxygen, which facilitates the damage done by light.
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References
- Photo Credit Dye image by vertellis from Fotolia.com
