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."

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

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.

> “ 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.

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

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

probably useful if you live in Seattle though =P

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.

isnt the sun the one yellowing those plastics?

Exactly my first thought, thank you for trying it!

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.)

or clothe washers.

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.

Similar recipe:

https://thebrickblogger.com/2020/06/restoring-discolored-leg...

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).

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....

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

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 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 :)

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?

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

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

You can buy blue led strips just about everywhere.

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.