Fat-soluble pigments
Some colours travel in oil rather than water. Washing a tomato or curry mark in water alone can leave it looking clean and set it permanently.
In detail
Pigments divide by what they dissolve in, and the division decides how a stain behaves. Carotenoids — lycopene in tomato, beta-carotene in carrot and sweet potato, curcumin in turmeric — are fat-soluble, not water-soluble. That single property explains the pattern people find baffling about them. A tomato mark rinsed in water looks better because the surrounding sauce washes out, and then reappears, because the pigment itself was never in the water. It survives a wash cycle for the same reason, and the heat of a tumble dryer then sets it permanently. Treating them therefore requires something that will handle an oily fraction — a solvent, or a detergent with a lipase in it — rather than water and agitation. Two further properties are useful. Carotenoids are readily oxidised, so an oxygen bleach works on them where mechanical washing does not, subject to the fabric tolerating it. And they are degraded by light, which is why an old tomato or turmeric mark on white cotton sometimes fades away in sunlight after every product has failed.
Why
- Tomato stain is explained by Fat-soluble pigments
- Mustard stain is explained by Fat-soluble pigments
- Chocolate is explained by Fat-soluble pigments
Two problems in one mark: the fat carries the colour, so a water-based attack moves neither.
- Plastic storage boxes is explained by Fat-soluble pigments
The orange is in the plastic, not on it. The box is stained and undamaged, and that is a distinction worth having.
Sources for this page
Sources
Spot Solver: spot and spill removal procedures
The Carpet and Rug Institute (CRI) · Trade or professional body
Relied on for: That tomato, ketchup and mustard entries include a vinegar solution and a spot removal kit rather than detergent and water alone. (states this directly)
Verification: a person has read the passage relied on.
Read on — Sprint 5-10: fifteen entries, stain by stain. Sprint 30: enumerated at 296 from the publisher's own sitemap, 134 more read plus 'Unknown'. Sprint 38: 56 more, chosen against stains the catalogue lacked. 192 of 296 read. Supports the claim as stated.
Royal Society of Chemistry educational and reference chemistry resources
Royal Society of Chemistry · Scientific literature
Relied on for: That carotenoid pigments are fat-soluble rather than water-soluble and are readily oxidised. (background and mechanism only)
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
Last reviewed by a person on .