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Removing yellowing from plastics - Part 2

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krye

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I just dipped my Mac SE mouse. It looks amazing now. It took less than 2 hours in 30% peroxide. I can't wait to do the whole machine.

Before:
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After:
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I also gave my Mac Plus a quick dip. It wasn't too bad, but it could stand to come down a notch.

Before:
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After:
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All the details and disassembly pics are on my site, ryemac3.net
 

Chuck(G)

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I've been following this thread with some interest.

Out of curiosity, has anyone tried oxalic acid instead of hydrogen peroxide? It's a great bleach for removing stains from wood and fabric.
 

krye

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I've been following this thread with some interest.

Out of curiosity, has anyone tried oxalic acid instead of hydrogen peroxide? It's a great bleach for removing stains from wood and fabric.

If it's some sort of bleach, then I would advise against it. Bleaching is bad, that's basically just stripping color away. The peroxide/oxy solution works because of some serious chemistry. There is a good read here as to why old plastic turns yellow. The fire retardants mixed into plastic changes color over time as it is exposed to UV light. So the oxy/peroxide isn't just "bleaching" it white". It is chemically altering the fire retardants in the plastic back to the color it was.
 

Chuck(G)

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Oxalic acid is a strong reducing agent, which can bleach. It's used a lot to remove rust stains in wood and to bring the color back to stained or discolored wood. So it's not a bleach in the same sense that, say, calcium hypochlorite is.

What's made me wonder about this discussion is exactly the chemistry. Hydrogen peroxide is a strong oxidizing agent, yet the source you cite states that the problem is oxidation. So if your H2O2 isn't bleaching, what's it doing? If the problem was oxidation, it would seem that a reducing agent, not a strong oxidizer, would be the answer.

I guess I'll have to try some oxalic acid to see if it works...
 

krye

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Here's my latest one. It does look a little patchy in spots, but I think the previous owner tried to clean it with something:

Before:
3020340281_75ac5ab336.jpg


After:
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Before:
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After:
3020340291_49363c0bda.jpg
 

Lorne

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Here's my latest one. It does look a little patchy in spots, but I think the previous owner tried to clean it with something:

What have you been doing (if anything) to protect the stickers/labels?
They seem to be fairing pretty well.
 

krye

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What have you been doing (if anything) to protect the stickers/labels?
They seem to be fairing pretty well.

Nothing, they get treated too. The bar code on the back of the SE faded a little bit and the ones on the back of the mice changed color a little bit. But it's not like they are getting destroyed.
 

Merlin

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What's made me wonder about this discussion is exactly the chemistry. Hydrogen peroxide is a strong oxidizing agent, yet the source you cite states that the problem is oxidation. So if your H2O2 isn't bleaching, what's it doing? If the problem was oxidation, it would seem that a reducing agent, not a strong oxidizer, would be the answer.

I guess I'll have to try some oxalic acid to see if it works...

The chemistry is all down to free radicals; the bromine has a single free electron in it's outer shell and it's not totally happy as Br-. What the bromine does is share an electron with an oxygen radical, so that the bromine appears to have eight electrons in the outer shell.

What the TAED does is catalyse the peroxide into hydrogen and oxygen (via peracetic acid, which is a powerful bleach) and it's the hydrogen radical (H+) we are putting onto the bromine, neutralising the single negative charge. The oxygen gets evolved and this is why the solution eventually gets spent.

That's how I understand it, anyway, it's a kind of weird reaction...
 

DimensionDude

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While walking through the parking lot at work today I had a thought; would the de-yellowing agent work on the clear (well, supposed to be clear) polycarbonate headlamps on automobiles?

Is that plastic yellowing in a different fashion than the computer cases?

Might be worth a try if someone has the chemicals and yellowed headlamps.

Kent
 

Lorne

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While walking through the parking lot at work today I had a thought; would the de-yellowing agent work on the clear (well, supposed to be clear) polycarbonate headlamps on automobiles?

Is that plastic yellowing in a different fashion than the computer cases?

Might be worth a try if someone has the chemicals and yellowed headlamps.

Kent

I have the chemicals, but thankfully a new enough vehicle that the headlight covers are still clear.
I have though, had success previously on old yellowed plastic light covers with a Plastic Polish. (It simply removes the layer of yellowed plastic).

Merlin would be the one to comment on the clear yellowed plastic, but he probably won't know what we're talking about because he never sees enough sun to realize that the clear plastic headlights do go yellow :). (My guess is that it's the same cause).
 

Unknown_K

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Here's my latest one. It does look a little patchy in spots, but I think the previous owner tried to clean it with something:

Before:
3020340281_75ac5ab336.jpg


After:
3020340287_f4a2bec2fd.jpg


Before:
3020340285_aff806fcd0.jpg


After:
3020340291_49363c0bda.jpg

I think you might be leaching the pigment out of the plastic and uncovering normal plastic flow (inside the mold when injected) swirls and other imperfections that normally do not show up. Basically you over cooked it.
 

nymetropolitans

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While walking through the parking lot at work today I had a thought; would the de-yellowing agent work on the clear (well, supposed to be clear) polycarbonate headlamps on automobiles?

Is that plastic yellowing in a different fashion than the computer cases?

Might be worth a try if someone has the chemicals and yellowed headlamps.

Kent

Best way to do that is wet sand and polish. Plastic headlamp enclosures come from the factory with a clearcoat somewhat similar to what's used on the painted surfaces and it yellows over time from various pollutants in the air and rain. You basically wanna strip that film away completely, or at least to a layer underneath where it hasn't yet been yellowed, however they're usually pretty thin. If you wanna go the extra mile, you can buy a spray on clearcoat and re-apply it after everything is shined up, so that the actual plastic isn't harmed in the future. I've done it on a few different cars and it almost always comes out looking amazing.

If you search around on Google a bit you can find directions, different people have different methods. Before I ever heard of wet sanding I actually just used rubbing compound and that didn't do a bad job either, but the yellowing tends to come back a lot quicker.
 

gerrydoire

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Yellow be gone...

Yellow be gone...

This is probably the most interesting topic I found so far when it comes to collecting vintage computer stuff, I bought an Apple IIC from some guy and it was blowtorched looking yellow, when i get the nerve I hope to try this de-yellowing method.

;)
 

krye

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I gave the SE another dip in the solution last night. The finish looks much better now. I also did the keyboard.

Before:
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After:
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3075142103_6b3f8e6ca9.jpg
 
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Lorne

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I think you might be leaching the pigment out of the plastic and uncovering normal plastic flow (inside the mold when injected) swirls and other imperfections that normally do not show up. Basically you over cooked it.

As Merlin has posted previously, you can't really over cook the pieces (except from too much heat). I've had a few pieces come out a little blotchy too. That happened using the brush on paste version. It never happened using just the liquid solution (and I over cooked some pieces to the point of warping from heat using that method, and they weren't blotchy). I think it's got something to do with the concentraction of the chemicals in sections of the paste - if it's not well mixed, the results can turn out blotchy. If you process them again, chances are that the higher concentration parts of the paste won't be applied on exactly the same spot, so reapplication should get rid of the blotches.
 

gerrydoire

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WOW!!!!!! I'm so glad I saw this thread.

Look for a demo on a very faded ProFile case soon!

-Jason

I plan to give it a try myself, with something small and of no real value to see how it goes.

Should be interesting.
 

Merlin

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Guys, I am writing up all about this to go in a ClassicAmiga Wiki article which I hope to put together over the weekend.

Any of you others who are trying this method out on your items, we want pictures; the more examples from different makes and models of cases etc. we have, the better.

Cheers

M
 

tezza

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More de-yellowing examples

More de-yellowing examples

Hi,

I thought it was probably better to use this old thread rather than make a new one.

Yesterday and today I tried out the de-yellowing process on a Vic-20. It worked a treat!!. I found a simple food thickener made a great paste, and hydrogen peroxide solutions of only 6% (hair bleach strength) are sufficient.

I've documented the experience in my blog.

Cheers

Tez
 

carlsson

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Wow, it really looks nice. Perhaps the strength of the hydrogen peroxide depends on which kind of catalyst you mix it with, or simply the strength of UV?
 
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