Photodegradation
Light breaks pigment molecules apart. It is why some hopeless stains disappear on a washing line, and why it also fades what you wanted to keep.
In detail
Ultraviolet and visible light carry enough energy to break the chemical bonds that make a molecule coloured, so pigments fade with exposure. In cleaning this cuts both ways and both are useful to know. As a treatment, sunlight is genuinely effective on several pigments that resist chemistry — carotenoids such as lycopene and curcumin degrade readily in light, which is why an old tomato, curry or turmeric mark on white cotton often fades away on a line after every product has failed, and why sun-drying whitens nappies and cotton bedding. It is slow, free and does not stress the fibre the way repeated bleaching does. As damage, the same process fades upholstery, curtains, carpet and vehicle interiors near a window, and it degrades the polymers themselves as well as the dyes, so a sun-exposed plastic or rubber becomes brittle and chalky rather than merely paler. Two cautions. Light-fading works only on the pigment, so it does nothing for a greasy or protein deposit. And on a dyed fabric it does not distinguish between the stain and the garment.
Why
- Mustard stain is explained by Photodegradation
- Mustard stain is explained by Photodegradation
Sources for this page
Sources
Royal Society of Chemistry educational and reference chemistry resources
Royal Society of Chemistry · Scientific literature
Relied on for: That coloured organic molecules are degraded by ultraviolet and visible light, and that carotenoid pigments are particularly light-sensitive. (background and mechanism only)
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
Leather Care and Cleaning Guide
The Leather Institute, 2011 · Trade or professional body
Relied on for: That direct sunlight is named as harmful to leather alongside direct and prolonged heat. (states this directly)
Verification: a person has read the passage relied on.
Read on — General care and cleaning instructions, basic and advanced cleaning technique, and the Suede section. Supports the claim as stated.
Last reviewed by a person on .