Removing yellow stains from fabric with blue light | Hacker News Reader

Removing yellow stains from fabric with blue light

phys.org

145 pointsbookofjoe82 comments

> 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...

As an aside, this technique is also used to remove the "yellowing" from Apple II computers:

https://youtu.be/aFGS9xaaO_M

There's even special formulas of hydrogen peroxide, arrowroot, and oxyclean, with raging debates on the proper ratios, how long to keep them in the sun, etc:

https://www.callapple.org/vintage-apple-computers/apple-ii/s...

I feel like the removal of yellowing from things like Apple II computers known colloquially as 'retrobriting' as showing in your video is more the use of peroxide compounds which are not used in the article.

"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."

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.

There is probably some math to do about the availability of free radicals from bleach versus a set period of sunlight at a certain time of year, in a certain part of the world.

I tried drying linens and clothes outside the first time I moved from an apartment (with strict controls on what can and cannot be seen on the balcony) to a single family home. I quickly stopped because there was so much dust that would accumulate on your freshly washed clothes in the time they were hung outside. That's not to mention bird poop or feral cats deciding to do some stretching on your sheets.

You need a sun room.

I agree. I like my sun room to be upstairs of the smoking lounge, but next to the library.

That's no longer "basic low tech from centuries ago" any more. Centuries ago there wasn't transparent glass, only colored glass (think stained glass in an old church).

There are some really striking paintings of it!

https://en.wikipedia.org/wiki/Flemish_Market_and_Washing_Pla...

Though I think this is possibly a depiction of a step in linen production, rather than the maintenance of used linen.

But anyway yeah it used to be a normal part of life people were used to seeing.

https://en.wikipedia.org/wiki/Bleachfield

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.

Was going to say. This is very well known way to get poo stains out of reusable nappies and baby wipes.

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

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.

Doesn't seem to be on the IARC's lists of known and probable carcinogens: https://www.cancer.org/cancer/risk-prevention/understanding-...

And yet local production of peroxides by inflammation is probably the causing agent most cancers.

Well, it's part of the cancer process; most cancers couldn't survive without it. But that's also true of, for example, local production of DNA, or anaerobic glycolysis, or angioneogenesis.

It's not true that if you expose tissues to lots of H₂O₂ they'll get cancer.

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.

Do you wear gloves when you handle your H2O2 cleaning laundry solution?

I dont, but I dont care.

I’m neither ingesting, inhaling, nor bathing in it, so I don’t care either, nor would I be concerned to wash my hands in it were it needed. Just drinking water or being outside is more than enough exposure to cancer to be worried about.

I'm also not a chemist... but I do have a PhD in mtls science from a top 10 program. My dissertation was on computational chemistry on organic compounds.

You're 100% right.

As long as the photon is energetic enough, it can cause a radical and therefore break a chemical bond.

Brighter the sunlight, more peroxides (or radicals) made, more damage to your skin or your cloth's fibers.

This is also why anti-oxidants are so effective at protecting the body, why inflammation is so damaging (body produces peroxides to eliminate what it believes is a threat), over consumption of food, too much/little exercise, etc. they all affect peroxide concentration or their halflife.

Nice to meet another Materials Science person. I only did bachelor's in Materials and Metallurgical Engineering. Hi:)

right, been glancing at this thread, and what occured to me is that blue light from LED's having a bleaching effect, specificly on yellow(cebum) organic compounds, then implys that it's not just(famously) hard on our eyes, it's frying them, and possibly worse. I certainly mind a brite screen, and keep it at the minimum level, except when in sunlight or useing my phone to show family and customers things. There are other effects to mass use of high powere LED's, where seagulls are flying around in downtown Halifax, NS in.the middle of the night, which I see now, but never happened with the old mercury vapour street lighting, which was it's own kind of wierd, in that it's bright yellow light from a distance, but makes everything under them monocromatic.IE: something in.the LED light wakes birds up.

In my experience no not really. I'm sure it has some effect but compared to chemical bleach or even just using a clothes dryer the wear is not noticeable.

When you do it with actual flax linen it is quite stiff afterwards and it may form permanent creases if you treat it in certain ways immediately after, depending on the weave. But that's to some extent always true with linen.

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.

The sun isn’t a blue LED

Blue LEDs aren't magic. They emit a narrow bandwidth of light, and the Sun emits all of that bandwidth of light and more.

I’m aware… I think you missed my point

The number of commenters who think UV light is the same as sunlight...

lol, right?

> “ 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.

A light filtering glass cover that lets blue through but not UV could work for the while still using sunlight.

probably useful if you live in Seattle though =P

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

isnt the sun the one yellowing those plastics?

UV can trigger the chemical reactions within the plastics that yellow the plastics, but UV + peroxide does a different chemical reaction to bleach them.

Both is true

Exactly my first thought, thank you for trying it!

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.

We used cloth diapers for our babies. Residual poo left yellow stains that the washing machine did not remove. Sunlight removed the stains completely.

So are they going to put blue LEDs in clothes dryers now?

It looks like a good idea. Do they survive the high temperature for hours?

(Also, the additional energy/heat will help drying, so you pay for the hardware but the energy consumption for the light is totally free.)

LED packages are designed to radiate the heat in the opposite direction of the light, and they would need to be sealed behind some barrier away from the damp clothes anyway.

Just make the fresh cold air from outside pass through the heat sink and then go to the red hot resistance and then to the cloth.

or clothe washers.

The report linked into the post gives an extra piece of information, the Watts.

> 445 nm; 1.25 W/cm2

1.25 watt/centimeter² ~= 853.75 lumen/centimeter², eg. not a terribly exotic brightness assuming you are ok treating a small area at a time. One of those small LED light panels would probably be in the right ballpark if you positioned it very close to the target.

Let's model a shirt with a cylinder, and let's flat it in to rectangle. Some 50 cm x 100 cm could be OK for a quick estimate. It's 5000 cm, so 6.25 kW if we want to make it work fast. The OP wrote about 10 minutes. Let's relax it to a little more than 1 kW not to be inconvenient to other home activities and we get a 1 hour time. Probably that will help with heat management too.

But 50x100 is not particularly large (think of bed linen) and yet it could take a lot of space in a house. Maybe some small area handheld device that one can apply to stains and leave it there until it turns off with a timer?

If there was a solution for sun-yellowed (originally white) Lego bricks I would be a major user!

My grandmother already did that putting clothes in the sun of Spain.

I suppose this also ages the cloth/material given that the color is getting oxidised similar to normal bleaching.

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).

... 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

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)

Related? Blue light and bilirubin excretion https://pubmed.ncbi.nlm.nih.gov/7361112/

What intensity is “high-intensity?” The article doesn’t give a number. Is this something that can be done with a few bright LEDs or do you need a specialized lighting array?

The abstract at https://pubs.acs.org/doi/10.1021/acssuschemeng.5c03907 mentions a power of 1.25 W/cm2

If you follow the links to the supplementary info it gives you intensity level, for example "The prepared dish was placed in a blue LED irradiation device and irradiated at 1.25 W/cm2 for 3 h."

As a reference, noon sunlight is very roughly 1000 W/m^2 or 0.1 W/cm^2, so this is pretty intense and I suspect would not be eye safe.

See https://pubs.acs.org/doi/suppl/10.1021/acssuschemeng.5c03907....

This is old common knowledge, why this is a paper? Everyone knows that exposing the clothes to the sun cleans many types of stains.

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.

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.

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.

I wonder if you could remove blue ink with yellow light. Specifically residue from ballpoint pens on furniture.

That would be an interesting one, I have a strangely related story that not too long ago my toddler drew _all over_ a yellow suede sofa with a blue ballpoint pen, was a nightmare to get it out without making the pristine sofa look like a drowned rat.

Tue sun is probably the most powerful blue light you can readily access. There's just a bunch of other colours that come with it.

Maybe I should have emphasised the word "artificial" rather than the word "blue", the implication was that it's not the only type of blue light, the sun being the obvious one.

The thing about the sun is, you get no light when there's no sun, and some countries don't even get daylight for several months of the year!

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?

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 :)

Be warned though that retr0brighting is an art. If done unevenly it looks worse than before.

rushes outside to undo the hasty application/test I did on my old miata soft top plastic

ty, too much coffee this morning

Is there a practical way today to use their findings with stuff we can buy at an hardware store?

https://news.ycombinator.com/item?id=45209124 mentions that simply putting the stained cloth under the sun works.

Buy some diy flashlight kit. There's an entire community of people that build flashlights for fun and hence a ecosystem of parts.

Then put in the strongest 455mm wavelength diode you can find off Digikey that fits the kit parts.

*nm, as in nanometers.

Haha, 455mm! That's 659MHz, which used to be channel 45 for UHF TVs in the US: https://en.m.wikipedia.org/wiki/Television_channel_frequenci... but has it been reallocated to something else like LTE?

https://www.spectrumwiki.com/wiki/display.aspx?f=659000000&l...

Don’t buy anything. Use the sun, for the moment it’s free.

Given the bits about UV, using the sun plus a glass window might be better?

I think standard glass blocks UVB and car windscreens often block UVA and UVB.

Or existing oxygen based cleaning products. The sun can cause other damage, it’s a balance

You can buy blue led strips just about everywhere.

Does it work on sunscreen related orange-ing? i.e. Avobenzone and iron?

Nice, but I need to remove coffee stains from like 10 different shirts

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