Removing yellow stains from fabric with blue light
46 comments
·September 8, 2025jondea
I'm surprised it isn't mentioned in the article, but you can get rid of yellow stains by putting your clothes out in the sun.
davidhyde
> “ After heating the swatches to simulate aging, they treated the samples for 10 minutes, by soaking them in a hydrogen peroxide solution or exposing them to the blue LED or UV light. The blue light reduced the yellow stain substantially more than hydrogen peroxide or UV exposure. In fact, UV exposure generated some new yellow-colored compounds.”
They did test with UV light. The sun is broadband (it will have both blue light and uv light) so it works to a degree. The insight is that uv generates some new yellow coloured compounds and only using blue light prevents this.
goda90
A light filtering glass cover that lets blue through but not UV could work for the while still using sunlight.
prism56
Was going to say. This is very well known way to get poo stains out of reusable nappies and baby wipes.
contrarian1234
A bit of a naiive question, but does this age the clothing?
For instance "color-bleach" (which I guess is peroxide with other stuff) makes cloths disintegrate if used too often
Guestmodinfo
I'm not a chemist but my two cents because I studied a course of Industrial Inorganic Chemistry in my college. My professor of that course used to say Hydrogen Peroxide is a very strong carcinogen. So I hate every Tom Dick n Harry that yaps about the goodness of Hydrogen Peroxide on YouTube or elsewhere without mentioning that it will give you cancer even in small amounts. And yes UV disintegrates the fibres so the more you keep your clothes in the sun or in UV then they will look old. Source: I live in India with too much UV andif I keep anything under the sun for a couple of days then it looks old or atleast no more new to be worn fashionably.
therealpygon
Your professor was teaching Industrial chemistry. At industrial (undiluted) strengths, there aren’t many chemicals that can’t damage tissue or potentially cause cancer. Constantly breathing the undiluted fumes or other exposures will certainly carry some risk in an Industrial application.
Washing clothes in a dilute peroxide solution is not going to cause cancer, therefore simply walking outside to hang your clothes carries substantially more cancer risk than the use of Hydrogen Peroxide.
Saying it causes cancer in “small amounts” is a bit like shouting at someone that stepping on a twig is destroying the entire forest…while standing next to an inferno.
nwellinghoff
Hydrogen Peroxide is not a carcinogen. People have been using for mouth wash for lifetimes with no negative effects. Who was this professor? Can you site a source?
kragen
Doesn't seem to be on the IARC's lists of known and probable carcinogens: https://www.cancer.org/cancer/risk-prevention/understanding-...
jama211
The sun isn’t a blue LED
refurb
What’s old is new again!
When I lived overseas my laundry was often dried in the sun and it’s amazing how fast the color is bleached out.
internet_points
probably useful if you live in Seattle though =P
MattBearman
I wonder if this is related to yellowing plastics? Retr0brighting with peroxide and sunbriting (putting yellowed plastics out in the sun) are already common treatments in the retro community. I’ll have to give it a try on some of my old hardware
emsign
This changes the best practice for retr0brighting from using UV or sunlight to 445nm blue LED. I already knew from anecdotes that sunlight seemed more effective than a UV lamp. People assumed it was the extra heat, which may or may not still be a contributing factor, but I guess it's the blue light prt of the sun's spectrum.
dahrkael
isnt the sun the one yellowing those plastics?
jama211
UV can trigger the chemical reactions within the plastics that yellow the plastics, but UV + peroxide does a different chemical reaction to bleach them.
emsign
Both is true
iwontberude
Exactly my first thought, thank you for trying it!
jldavern
Blueing using blue dyes has been a pretty common laundering technique for whitening clothes for some time https://en.m.wikipedia.org/wiki/Bluing_(fabric)
pmontra
The report linked into the post gives an extra piece of information, the Watts.
> 445 nm; 1.25 W/cm2
donperignon
This is old common knowledge, why this is a paper? Everyone knows that exposing the clothes to the sun cleans many types of stains.
alias_neo
It's news to me that the sun is blue!
Jokes aside, I suppose it's novel in the sense that it can be achieved with artificial _blue_ light.
My understanding was that it was various forms of UV from the sun that caused "bleaching", whereas the paper points out that it is not UV in this case, and in fact, the UV can cause additional staining.
EDIT: Edited for grammar.
blensor
I haven't read the paper only looked at the first page with the two sheets, but I think the novel idea here is that it's using complementary colors.
Take a color that is maximally absorbed by the stain and thus get the most energy into it without affecting too much else.
I wonder if that would work with other colors as well.
alias_neo
It's an interesting idea, and how it would work with colours other than "bleached" would be the interesting part.
Presumably it wouldn't work on black without fading the garment, but given how we've seen things fade in shop windows, I wonder if there's some novel applications for removing other types of intentional "stains" like ink, or paint, and particularly if they're under/behind a surface like a clear-coat or glass or something else that prevents physical access.
Reubachi
I am a common "poo-pooer" of bad submissions on here, and comments not in good faith
But this paper taught me something I had no idea about as a 33 year old. Also in the comment chain someone mentioned/brought up using peroxide/sunlight to clear up old yellowed plastics which is....monumental to some of my projects :)
emsign
Be warned though that retr0brighting is an art. If done unevenly it looks worse than before.
llm_nerd
Ultraviolet light is ionizing. Things oxidize and often whiten in sun because the UV light (the part of the UV spectrum as you go below ~315nm) ionizes and causes chemical reactions, in most cases by splitting O2 which is then charged O atoms that want to react with things.
445nm light isn't ionizing at any brightness, and shouldn't be catalyzing oxidation. Didn't look at it in detail but what is their claim on mechanism?
aeonfox
So are they going to put blue LEDs in clothes dryers now?
colechristensen
> The blue light reduced the yellow stain substantially more than hydrogen peroxide or UV exposure. In fact, UV exposure generated some new yellow-colored compounds.
Here's the key piece of information for me, it's not just light doing this or higher energy blue being close enough to UV to get things done, the blue light tested outperforms UV at destroying some of these yellowing compounds.
It would be nice in followup research to see Figure S8 [1] with an additional dimension for irradiation with various frequencies, not just 445 nm.
It looks like Amazon has some "therapy bulbs"[2] close to the correct frequency for $30, now I wish I hadn't thrown away some of those old yellowed pillows so I could do some science.
1. https://pubs.acs.org/doi/10.1021/acssuschemeng.5c03907
2. https://www.amazon.com/Aumtrly-Light-Therapy-Irradiance-Cove...
cladopa
My grandmother already did that putting clothes in the sun of Spain.
amelius
Nice, but I need to remove coffee stains from like 10 different shirts
N_Lens
I suppose this also ages the cloth/material given that the color is getting oxidised similar to normal bleaching.
Etheryte
I would not expect the effects to be in the same ballpark. Bleaching is very harsh, to the point where I wouldn't want to put my hand in a jug of bleach. I could imagine holding my hand up to a strong light. Sure, it might get too hot or too uncomfortable eventually, but at least in my mind, I would expect it to be lesser (so long as we don't talk about a literal deathray lamp).
contrarian1234
... have you never washed your own clothing?
You don't use concentrated bleach on clothing... You diluted it. It's only provided concentrated for storage convenience
ljsprague
Does it work on sunscreen related orange-ing? i.e. Avobenzone and iron?
This is basic low tech from centuries ago, people used to spread out wet sheets on fields of tall grass.
I dry my linens outside (I'm not American), and no chemical bleach beats the effectiveness of the sun turning oxygen and water to peroxide.