How to remove yellowing from an old Atari case

[AndyR]

Coming late to the game here, but this stuff is just too cool.

 

Any pigments in the plastic are completely unaffected by the gel as long as you keep the strength of the hydrogen peroxide below 15%.

 

Not to nit, but I can't imagine this is strictly correct. The peroxide (and the UV light, for that matter) will, in fact, break down many/most pigments, no? And there's nothing magic about 15% -- any concentration will have that effect at some rate; you're just trying to pick a sweet spot between speed of debromination and collateral damage to the existing coloration.

 

Has anyone tried a controlled study? Maybe hack up an existing piece of plastic and try strips in different concentrations of H2O2, then cut them in cross section after treatment to compare with the original/interior color. Actually I guess there are four variables: exposure time, UV strength, and H2O2 and Oxy concentrations. Any guesses as to a model for deciding what the right mix would be?

 

Metal badges or painted decals shouldn't be affected as Mimo says. I would go for electrical tape for masking metal decals if you aren't sure as the adhesive isn't strong enough to lift the paint.

 

How about trying a soluble finish, like shellac? Paint it on before the treatment, and strip it off later with ethanol. The seal is obviously going to be better than tape, and you can control with much better precision where it's going. I can even see the more adventurous hand-painting the lettering on their keys.

 

Certainly the ethanol won't affect the ABS or any of the paints used on the case. Although if there are tiny holes or scratches that will collect paint, washing it off may be annoying.

[Merlin]

@ AndyR

 

Fair enough, but on the subject of pigments, most of the pigment is encapsulated in the resin and is therefore intert, unless the polymer immediately next to the pigments particle degrades and the amount of this would be negligable.

 

We have done controlled experiments already on scrap parts.

 

Exposure time can be as long as you like, although UV can be a foe as well as a friend, as this helped to cause the yellowing in the first place. UV can also degrade ABS plastic to the hydroperoxide, via spare butadiene bonds on branches of the polymer. ABS is a terpolymer (made of three monomers) and isn't a consistent material, no two batches are the same, even though you may load the same percentages of monomers.

 

UV strength is important and if speed is what you are after, the more of it the better while you are treating the parts. Afterwards, an anti-UV coating would slow or even stop the return of yellowing.

 

H2O2 strength does matter as higher strengths >20% may cause degradation of the polymer. The ABS polymer can degrade to the hydroperoxide over many years and high peroxide strengths can bleach this via peracetic acid, which is one of the imtermediate products formed by TAED as it works as a catalyst. The result can be a permanent white "bloom" on the surface of the plastic; not good. Keeping the strength below 15% ensures that this risk of "bloom" is minimised with a safety margin for errors in mixing the correct strength.

 

As stated above, the Oxy is a catalyst and the active ingredient we need (TAED) is only soluble up to 1.5 grammes per litre. Adding lots of Oxy would speed up the catalytic reaction but it also foams up a hell of a lot, due to detergents and surfactants added to the Oxy formulation. I have some neat TAED and adding this causes no foam at all, although most people won't be able to get hold of the neat material and I'm sure that the postal services may not appreciate lots of little sachets of white powder being sent everywhere; I don't need my front door kicked in by the Drug Squad, thanks

 

You can get paintable, low-tack masking materials from craft shops; coating the decals first with lacquer before treating the case is a good idea.

 

I hope that this has answered your questions.

Edited February 14, 2009 by Merlin

[Merlin]

I have now updated the Wiki article with some of the scientific explanation. I've not gone too heavy on the science, I have used just enough to explain what i need to.

[Merlin]

Just to show how much of an anorak I have become about this topic....

 

Have you ever seen black bumpers (fenders) on cars, that gradually turn grey then white under sunlight? Well, that's because the bumpers are made of...yes, you've guessed it.... ABS.

 

The years of direct UV light gradually degrade any free double bonds from the butadiene parts of the ABS down to the hydroperoxide and the manufacturer's don't put enough carbon black pigment into the material to mask this.

 

The only ways I know to fix that are either black liquid shoe polish or matt black paint; the whitening is irreversible as far as I know, unless someone wants to prove me wrong.....

Edited February 16, 2009 by Merlin

[Longhorn Engineer]

Just to show how much of an anorak I have become about this topic....

 

Have you ever seen black bumpers (fenders) on cars, that gradually turn grey then white under sunlight? Well, that's because the bumpers are made of...yes, you've guessed it.... ABS.

 

The years of direct UV light gradually degrade any free double bonds from the butadiene parts of the ABS down to the hydroperoxide and the manufacturer's don't put enough carbon black pigment into the material to mask this.

 

The only ways I know to fix that are either black liquid shoe polish or matt black paint; the whitening is irreversible as far as I know, unless someone wants to prove me wrong.....

 

Oh I wish someone would figure that out. My jeeps fenders are all gray. Need to spray paint them sometime.

[Rybags]

I was at my Hairdresser the other day, and asked her about the Hydrogen Peroxide she gets.

 

She showed me, and squirted some out... it was like a gel in consistency, and she said the only ingredient listed was Hydrogen Peroxide, 6%

 

Any ideas here? Would this stuff work with some Oxy mixed in, using the gel-application mode?

[+Guitarman]

I was at my Hairdresser the other day, and asked her about the Hydrogen Peroxide she gets.

 

She showed me, and squirted some out... it was like a gel in consistency, and she said the only ingredient listed was Hydrogen Peroxide, 6%

 

Any ideas here? Would this stuff work with some Oxy mixed in, using the gel-application mode?

 

I was going to ask about this also. The Sally's I picked up the 40vol from (12%) has the creme version of the same stuff. Wonder if that would work in place of needing the Xathan??

[MaXKiLLz]

I'm really concerned now. I had my Atari 800 case outside for 2.5 hours with the correct mixture and I'm getting some strange results. Take a look. The darker areas match the inside of the case perfectly. The much lighter areas are almost white. Have I ruined this my removing the case color completely in those light areas? Please tell me there is some way to reverse this or that it's just residue. I've washed the plastic with mild dish soap and warm water, with no improvement.

 

1 pint Hydrogen Peroxide (Sally 30 Volume)

1 teaspoonful xanthan gum

1/2 teaspoonful Oxy

1 teaspoonful glycerine

[+Guitarman]

2.5 hrs is not nearly enough to get the results you need. I have noticed in the cases I've done that early on, there will be some patching as parts of the case react a bit faster than others, based on the uniformity of the gel coating. It all tends to equal out after a while.

[MaXKiLLz]

2.5 hrs is not nearly enough to get the results you need. I have noticed in the cases I've done that early on, there will be some patching as parts of the case react a bit faster than others, based on the uniformity of the gel coating. It all tends to equal out after a while.

 

 

It's just that I can't remember the Atari 800 being as a light a color as some of the light areas I'm seeing after 2.5 hours. The areas that are appearing very light right now are much lighter than the color inside the case that has had no exposure to light and no yellowing. I've set the pieces back outside and will have it out there for the rest of the afternoon and see what happens. I just don't want to end up with a white Atari 800, because that definitely is not the original color. I'm interested in hearing more thoughts on the subject from different people. I'm quite nervous right now as this is my original computer purchased for me in 1981. I'd hate to have ruined it.

[Merlin]

OK, let's take this from the top....

 

Where exactly are you in the World? You haven't said, so I don't know what your local conditions are.

 

1. When you made the gel up, did you use 10 to 15% peroxide by diluting it, or did you use it straight from the bottle - what strength was stated on the bottle, as 30 volume is probably 30 to 35% which is way too strong.

 

2. What weather conditions were there (temperature and sunlight especially)?

[+Guitarman]

@Merlin

 

I don't know about over in the UK, but here, volume doesn't equal %. 10vol=3%, 20vol=6%, 30vol=9%, 40vol=12% and 50vol=15%. It sounds like he's using a 9% solution. I noticed some patching early on with my 810 case which equaled out after the 8 hours. I also did the top half a second time.

 

@MaXKiLLz

 

Part of the problem may be, while using sunlight, the mixture is drying out too quick. This is why a UV light of some sort is better. You don't have the heat factor with the lamp so the mixture stays moist.

 

 

OK, let's take this from the top....

 

Where exactly are you in the World? You haven't said, so I don't know what your local conditions are.

 

1. When you made the gel up, did you use 10 to 15% peroxide by diluting it, or did you use it straight from the bottle - what strength was stated on the bottle, as 30 volume is probably 30 to 35% which is way too strong.

 

2. What weather conditions were there (temperature and sunlight especially)?

Edited February 17, 2009 by Guitarman

[Merlin]

Thanks Guitarman, that's cleared up the strength issue anyway. I saw a big yellow thing in the sky once, but it scared me because it always rains here, so I went back to my UV lamp.......

[MaXKiLLz]

Here's exactly what I'm using. I'm located in South Florida, USA with the following weather conditions..

 

72°F - Winds: ENE at 14mph - Partly Sunny

Humidity: 39% - Dew Point: 46° F - Pressure: 30.19 in

Max UV Index: High (7)

 

I'm reapplying the mixture every 30 minutes to keep it wet. Should I just continue with the process and see what the end result is? I'm just concerned that I've somehow damaged my prized possession. I've followed the directions on this forum and the Amiga board forum as perfectly as possible. Let me know you thoughts.

 

[+Guitarman]

I'd just continue. The 30vol 9% peroxide will take a bit longer than the 12-15%. When I did mine, I applied the mixture in the evening and left it under a UV all night. I then put the case in the dishwasher and ran it through a short cycle with no soaps and let it clean and rinse all the mixture off. I came out looking great (and clean!!).

[Merlin]

They wouldn't sell stronger peroxide than 12% for hair use without having to put warning labels on the bottles, so I guess you are OK. The other ingredients look spot on.

 

Stick with it until the end of today, then wash the gum off and let's see the result.

[Merlin]

I then put the case in the dishwasher and ran it through a short cycle with no soaps and let it clean and rinse all the mixture off. I came out looking great (and clean!!).

 

 

How did you manage to climb into the dishwasher with the case?

 

Come on, post a picture of your result to help MaXKiLLz along and make him feel better, please.....???

[+Guitarman]

The pics were posted earlier in the thread, the 810 case and the 1200XL. Doing a couple more this evening.

 

I then put the case in the dishwasher and ran it through a short cycle with no soaps and let it clean and rinse all the mixture off. I came out looking great (and clean!!).

 

 

How did you manage to climb into the dishwasher with the case?

 

Come on, post a picture of your result to help MaXKiLLz along and make him feel better, please.....???

[mimo]

@MaXKiLLz

Have you washed off the residue?

When I did my 400 it looked similar to your 800 until I gave it a good wash (like Guitarman I like to use the dishwasher)

[AndyR]

I'm just concerned that I've somehow damaged my prized possession

 

Honestly, this is a concern of mine too. Despite some of the assurances I'm reading here, everything I understand of the chemistry involved here tells me that the TAED/H2O2 mechanism is a bleach, and will attack pigment molecules. TAED is not a pure catalyst here, it's breaking down in the presence of the peroxide molecules to form other molecules that act as bleaches for its intended (laundry) targets.

 

Some of the screenshots in the linked threads seem to argue similarly: the streaky top on the RX-8800, the overbleached Amiga keys, and the (to my eyes) much-whiter-than-original Osborne seem to indicate that at least some pigments don't work well with this process. It may be that the one used in the 800 is one of them.

 

Honestly, I'd suggest a lot more experimentation before using this on precious items to see if the bleach effect can be mitigated. One idea would be to increase the UV flux: that's the mechanism that detaches the bromide ions so they can be fixed by the peroxide, so adding more UV should increase the debromination rate without requiring more peroxide. Of course UV itself will attack the pigments too, but that's a much slower process -- you can leave most items in the sun for days without noticeable color change, in my experience.

 

And on the subject of UV: what wavelengths are we looking for here? Is there a specific bromine resonance we're hitting? Merlin seems to be using a black light, which uses a phosphor that is almost exclusively in the UVA band. There are also UVB fluorescent lights (sold as vitamin D boosters for reptile cages) out there, and also mercury vapor bulbs that emit (comparatively dangerous!) UVC for sterilization purposes. Obviously the black light works, but would the others work better? How broad is the bromine absorption band?

[Merlin]

@ AndyR

 

We are aiming for about 620 to 650nm, which is the region that excites bromine molecules. I agree in that one of the imtermediate breakdown products of TAED is peracetic acid which is a strong bleachine agent, however, we are keeping the amount of that to a minimum; the only destructive bleaching I've seen is when people have used 30 to 35% H2O2; at the levels Maxkillz is using, the reaction will favout the bromines and the TAED is pushing the reaction, not the strength of peroxide. I am using a standard black light which I believe gives out UV-A.

 

I can't speak exclusively for Terry Stewart at Vintage Computer Forums, however his experiments are posted in a blog and you can ask questions in the blog. For my own part, the test I did on the C64 case used 35% H2O2 and 1/2 teaspoonful per pint of Oxy and a UV lamp, and you can see from the eight hour picture that threre isn't a trace of bleaching on the treated side; If bleaching of the pigment or hydrolysis of the polymer was an issue, surely it would have shown itself with this extreme test?

 

Sometimes, I wish I had had as much help with this as I have had criticism; at EAB and VCF we have worked hard over months to get to where we have and this has been with people giving us a hard time all along the way.

 

Andy, I don't wish this to be taken as me being offended, but have you any suggestions as to how this idea could possibly be improved? Harpo certainly endorsed what we were doing scientifically earlier in the thread, and to date I have had no reason to mis-trust the more dilute peroxide solutions used as a gel.

 

 

@ Maxkillz

 

I suggest you stop your process now and if you have a dishwasher, put it through as Guitarman has said. If you are worried, the best thing to do is stop.

[AndyR]

We are aiming for about 620 to 650nm, which is the region that excites bromine molecules.

 

Typo maybe? That wavelength is kind more red-orange then UV.

 

Sometimes, I wish I had had as much help with this as I have had criticism; at EAB and VCF we have worked hard over months to get to where we have and this has been with people giving us a hard time all along the way.

 

Honestly, you're being way to thin-skinned here. In science, criticism is help. It's possible to be both excited about an idea and wrong about it at the same time, which is why one should always view exciting ideas with some suspicion.

 

I don't wish this to be taken as me being offended, but have you any suggestions as to how this idea could possibly be improved?

 

The "add more UV and reduce peroxide concentration" suggestion was exactly that, no? The hypothesis works like this: all the "bad" effects are due to the TAED/H2O2 reaction, but the reaction rate is presumtively the product of two quantities: the number of bromine atoms knocked loose per second in a given volume and the number of peroxide radicals in the same volume available to combine with them. So the idea is you can get away with half the peroxide if you double the UV flux. Does it work? No idea, it's a hypothesis, and a suggestion for experimentation.

 

Harpo certainly endorsed what we were doing scientifically earlier in the thread, and to date I have had no reason to mis-trust the more dilute peroxide solutions used as a gel.

 

Except, you mean, for the "misfires" I mentioned earlier (bleached keycaps, streaky RX-8800, and vampire-pale Osborne), along with the Atari 800 above. Most previous over-bleach effects have been explained away as a result of too much peroxide, but it's not at all clear to me that this is the case with all of these. I think there's more to this reaction than is being assumed.

[MaXKiLLz]

Well, I ran it thru a cycle on my dishwasher without soap and it did not improve the situation. My wife suggested I try Mr. Clean's Magic Eraser. I was very doubtful it would do anything. But to my amazement, I'm seeing a marked improvement. It's removing the what appears to be a white residue. I assume the peroxide. But it's taking quite a bit of elbow grease to get it off. Could it be the fact that I applied about ten coats of the mixture, every 30 minutes, as it continually dried again and again in the sun? Any suggestions from the chemists on making this residue removal easier. There were large white powdery drip marks surround the area that I was rubbing. It's definitely something on the surface. I don't believe the plastic as been bleached away. If that were the case, I would not be seeing these improvements. Your thoughts please.

 

I tried to photograph it but it just doesn't show up well on the digital photos.

Edited February 18, 2009 by MaXKiLLz

[+Guitarman]

I would still say that the better result will be with a UV light. Since I haven't tried the process in the sun (winter in Carson City!!!), I can't comment on the effects. But I would assume that the heat factor of using sunlight will cause the mixture to dry out. Applying more mixture is just covering whats dried and not really helping the surface a whole lot. Most that have used sunlight tend to clean the dried residue before applying another coat.

 

My UV light I have, I got at a pet store. It is for reptile habitats, works great and is only about $15.00. I would really try using something like that and remove the heat factor.

 

[+selgus]

I started out today with a plan to do a few cases; a 800xl, 1050 and a power block. I was going to use sunlight for my UV, being here in central Florida, but with the reports of the mixture drying out during the procedure, I am going to use my black-light.

 

In prepping my cases, I did a first pass with the magic eraser and it actually did remove a lot of years of weathering from the plastic, though not the yellowing yet. I would recommend doing this step first, or does the Oxy accomplish the same results?

--Selgus