Mustard stain
Coloured by turmeric in most prepared mustards, and curcumin is a pH indicator — which is why an alkaline cleaner turns a yellow mark red.
In detail
Most prepared mustards are coloured with turmeric, and turmeric's pigment is curcumin, which behaves as a pH indicator: yellow in acid and neutral conditions, and red to reddish-brown in alkaline ones. That single fact explains the experience people describe as the stain getting worse when they treat it. An alkaline cleaner, a soapy solution or an ammonia-based product shifts curcumin into its red form, so a pale yellow mark on a shirt becomes a conspicuous orange one, and the change is often mistaken for the stain setting. It reverses on acidification, which is why the carpet institute's mustard entry includes a vinegar solution and why rinsing thoroughly matters as much as treating. The same chemistry governs curry and turmeric marks generally. Curcumin is also strongly light-sensitive, and prolonged daylight fades it more reliably than most household treatments — a genuinely useful last resort on a white cotton item. It stains plastics readily and more or less permanently, which is why a turmeric-coloured food container does not recover.
Why
- Mustard stain is explained by pH indicators in stains
- Mustard stain is explained by Fat-soluble pigments
- Mustard stain is explained by Photodegradation
- Mustard stain is explained by Pigment retention
- Mustard stain is explained by Photodegradation
Hacks and claims involving this
- Leaving a stain in the sun to fade it Plausible mechanism, untested in this application
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 mustard routes through a detergent solution, a vinegar solution, warm water and a spot removal kit before a professional. (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 curcumin changes colour with pH, being yellow under acidic conditions and red under alkaline ones. (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 .