Cheap, easy and effective whitener for yellowed plastic items

[Axtman]

You guys probably already know about this trick but I will restate.

I took a few badly yellowed knobs of the test gear and put them in a baggie (Ziplock clear plastic bag). I then poured filled up the baggie about 1/2 way with 3% hydrogen peroxide (commonly found at drugstores). I then placed the baggie in the sun for a few days. The knobs came up much whiter than before.

This technique has been used by retro gamers and computer collectors to brighten the bodies of old yellowed games and computers.

[Axtman]

The button on the top was whitened with the procedure I discribed. The button on the bottom was what the other button looked like.

(The button looks whiter in real life.)

[Haenk]

You might want to google "retrobright".

[Ian.M]

... then note what opinions museum conservationists have on the process.   There is a serious risk of embrittlement, and old ABS may be pretty weak to start with!

[EE-digger]

RetrObright had a number of chemists and others analyze the cause and come up with their solutions, including a gel recipe.

Here's another take on the "whitening" however.  For me it worked on 3 or 4 products, but only from a certain timeframe...

I had several Fluke instruments which were already toward brown/amber when I acquired them.  Never having heard of the brightening efforts at the time, I tested the surface of one with full strength purple cleaner.  When sprayed onto the surface, the brown literally rained down the sides of the instrument.  It did not soften or affect the surface, even if an area was gloss, so I continued.

The units looked like new when cleaned this way and I concluded that the discoloring was from years of cigarette smoke.  I suppose it could also have been from some process that was running in a plant, leaving deposits on bench instruments and lungs over time.

[grumpydoc]

I tested the surface of one with full strength purple cleaner. 

WTF is "purple clearner"?

Is it a reference you chaps across the pond automatically understand?

Cigarette smoke certainly leaves brown tar stains which come off with a variety of cleaners, IPA is quite good.

[TimFox]

Does Google function on your side of the Atlantic?

[grumpydoc]

Y' know it would have been just as quick to provide an answer as expend the effort in a sarcastic reply.

Anyway checking the composition the stuff has hydrogen peroxide in it so not surprising it lightens browned ABS.

[TimFox]

My response was no more sarcastic than yours.  Nyaa-nyaah!

[tooki]

My response was no more sarcastic than yours.  Nyaa-nyaah!

No, your response was decidedly more sarcastic. FWIW I am American and I’d never heard of “purple cleaner”, either. And a google search doesn’t seem to indicate it’s a specific brand name to begin with.

[TimFox]

Googling “purple cleaner” gives many hits on “Purple Power^TM” and other similar products with “purple” in the name. 
I submit that “on your side of the Atlantic” and “you chaps across the pond automatically understand” are roughly equivalent in sarcasm, but extra credit for “WTF”.

[grumpydoc]

Ah, I see part of the problem.

“you chaps across the pond automatically understand”

Was not at all intended as sarcasm, it was a genuine query as to whether it was sufficiently well known in the US that no further explanation was needed.

Apologies for over use of British English

[TimFox]

I find the differences between British usage and American usage of the English language a fascinating topic.
"Rubber", "napkin", etc.
Of course, the brand names for normal household products have not yet become thoroughly globalized, but "Persil" is now available in the US (since 2015).

[TerraHertz]

Australian... who also has no idea WTF is "Purple cleaner."   Also aware that short, generic terms like that don't work well with google, and expecting to have to wade through piles of trash results. Also google results tend to be optimized for your own country, so might not even work at all for something like that.
When people refer to commercial products, I wish they'd be more specific, since brand names rarely remain the same in different countries. Or can be entirely different products.

Is this what you meant?
https://www.amazon.com/4320P-Industrial-Strength-Cleaner-Degreaser/dp/B002HU5N4O
https://www.walmart.com/ip/Purple-Power-Concentrated-Industrial-Cleaner-Degreaser-32-oz-Gel-Floor-use/16879847
Purple Power (4320P) Industrial Strength Cleaner and Degreaser     Brand: PURPLE POWER

[Haenk]

Of course, the brand names for normal household products have not yet become thoroughly globalized, but "Persil" is now available in the US (since 2015).

Lol, took Henkel only a century then?

[Paceguy]

That "purple cleaner" that is being referred to, is it possibly that Zep branded heavy duty degreaser that I use that happens to be purple in colour?

[Bravo]

I am amazed that the topic of purple cleaner has had that much discussion. Methylated Spirits. 

[Renate]

Semi-related:
I had a little white Bluetooth speaker that I ignored for a few years.
When I pulled it out of a box it was both yellowish and unpleasant to the touch, as if somebody had spilled something on it.
It turns out that it originally had some sort of "soft touch" coating that gave it a softer feeling, a matte look.
Apparently it had all decomposed into something else.
It was tough removing every speck of the nasty stuff using isopropyl.
In the end I had regular, non-matte, semi-shiny, smooth cheap white plastic.

I have a Snark guitar tuner which is also losing a similar coating.

[SoundTech-LG]

Here's the purple list ingredients for all the smart asses...  CLOROX2 but no bleach.

https://smartlabel.labelinsight.com/product/6096219/ingredients

[tooki]

Here's the purple list ingredients for all the smart asses...  CLOROX2 but no bleach.

https://smartlabel.labelinsight.com/product/6096219/ingredients

So now you’re saying Clorox stain remover is the “purple cleaner”? Which is different from what other people have said?

So maybe people weren’t being smartasses by asking for clarification for what is meant by “purple cleaner”, because it’s NOT a commonly-known term.

[Renate]

"Purple cleaner" is completely unambiguous. It clearly refers to:

[tooki]

"Purple cleaner" is completely unambiguous. It clearly refers to:

Of course. I should have remembered, my bad! You can throw the chancla at me now…

[Renate]

Of course. I should have remembered, my bad!

Actually, I was just kidding. I have no idea what they meant.
Still, that's the only purple cleaner that I know.