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Removing Yellowing from Plastics - Part 4

Yes, I agree. I would hardly call Merlin's comments slanderous, and a reply along the lines of "No, I'm not offering it as a service but I did treat a case for a friend" would have stopped the matter dead. Presumably the de-yellowing worked and the friend was happy. The "your pathetic Retrobright crap" comment is not only petulant but wrong. The process was a breakthrough now enjoyed by many.
 
I accidentally started something with a previous post, and I now need to stop it.
We don't need this thread getting edited, posts deleted, or even worse the thread locked, which if it turns into another of the rant type threads (and it could easily head that way) may very well happen.

Suffice to say, If I ever do something for one of you "as a favor", and then charge you "a reasonable sum", I don't think you should consider me a friend.
(PS: I'm keeping my avatar, with one person in mind).


Now, to change the subject, and hopefully get us back on topic with this thread (and what this thread is all about), have a look at this:

Before.JPG

It's a TeleVideo 950 terminal.
Probably the most yellowed piece I've ever had.

And here's what I was dealing with up close:

Before - piece.JPG

I'm processing this one in sections, and it shows the difference very well.

Partial.JPG

I'm getting good results, and it may be due to something that I'm doing differently.
It's a little more time consuming, but I've been checking the piece every hour to make sure the paste hasn't dried out or started filming. As soon as it has, I brush it again, and add more paste as necessary. I'm also brushing in a North South direction one time, and an East West direction next time. I'm getting none of the "bloom", and I think that may be due to the overlapping N-S, E-W brush strokes. Then again, it could also be due to the type/mix of the plastic used to make the piece. I'll know better once I or someone else gives it a try on a different computer's plastic.
 
It's quite simple... if someone treats a case as a 'favour' and things head South with their pride and joy, I just know where the support questions will get asked, that's all..

Like Lorne said, leave it; it's tomorrow's chip wrappers now as far as I'm concerned.....
 
Lorne said:
I'm getting none of the "bloom", and I think that may be due to the overlapping N-S, E-W brush strokes. Then again, it could also be due to the type/mix of the plastic used to make the piece. I'll know better once I or someone else gives it a try on a different computer's plastic.
Click to expand...

Yes, althought the symptom is not common, it would good to sort this coloured-cases "bloom" issue out. There could be a combination of reasons...type of plastic, drying out to quickly with the paste etc. Perhaps it's a combination of those things. It really needs some replicated experimentation/trials to see if factors can be isolated.

It would make a good research project for a postgraduate chemistry student.

Tez
 
tezza said:
It would make a good research project for a postgraduate chemistry student.

Tez
Click to expand...

Or, maybe you or me.
I concentrated on physics in high school. Never bothered with chemistry or biology. I'm getting my chemistry lessons (via Merlin) now.
However, now I would have preferred to have concentrated on electronics, but of course with a mimeograph machine in the school office, there wasn't a lot of opportunity for electronics instruction.

I'm going to try some Apple plastics with the N-S, E-W stuff next (IMO de-yellowing Apple stuff is a waste of H202 :) but, for the cause...)
 
I can field this one. The most plausible explanation I can come up with is that ABS can have free butadiene C=C bonds present even after masterbatching and moulding. These can oxidise and become the peroxide of ABS, either quickly via the oxygen free radicals liberated during the catalysing of H2O2 by the TAED, or more slowly by atmospheric oxygen over time. The dead give away is that the areas of highest discolouration are also the areas that are most likely to 'bloom'. Take a look at tezza's RX-8800 case photos in the Wiki, to the right of the large circular mark - that's exactly what I'm talking about.

So, the most likely conditions that will cause 'bloom' are a badly yellowed case being treated with a high concentration of H2O2 in the Retr0bright mixture. Does this sound like a plausible scientific explanation to you?
 
Merlin said:
I can field this one. The most plausible explanation I can come up with is that ABS can have free butadiene C=C bonds present even after masterbatching and moulding. These can oxidise and become the peroxide of ABS, either quickly via the oxygen free radicals liberated during the catalysing of H2O2 by the TAED, or more slowly by atmospheric oxygen over time. The dead give away is that the areas of highest discolouration are also the areas that are most likely to 'bloom'. Take a look at tezza's RX-8800 case photos in the Wiki, to the right of the large circular mark - that's exactly what I'm talking about.

So, the most likely conditions that will cause 'bloom' are a badly yellowed case being treated with a high concentration of H2O2 in the Retr0bright mixture. Does this sound like a plausible scientific explanation to you?
Click to expand...

God, I hope you don't talk like that while you're having a pint with the boys.

So, what if all the areas are completely discolored?
I'm a bit touchy on this one because I've always used the high (30%) concentration of H202, and have had mostly good results (except with Apple crap).
I suppose I could thin it down a bit, but that goes against my experience/instincts.

Or, are you saying that some plastics, like the Apple plastic, should have a lower concentration than the other plastics?

I can do some tests (and probably will now).
 
EDIT: arg... my bad.

EDIT2: and to keep this on track... I have found that some Apple plastics seem to be more sensitive to high H2O2 concentrations, but this might just be because my most heavily yellowed case plastics were Apple.
 
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Lorne said:
God, I hope you don't talk like that while you're having a pint with the boys.

So, what if all the areas are completely discolored?
I'm a bit touchy on this one because I've always used the high (30%) concentration of H202, and have had mostly good results (except with Apple crap).
I suppose I could thin it down a bit, but that goes against my experience/instincts.

Or, are you saying that some plastics, like the Apple plastic, should have a lower concentration than the other plastics?

I can do some tests (and probably will now).
Click to expand...

LMAO!! No, I do manage to get out a bit, you know.....;)

What I am suggesting is that parts that are as badly discoloured as Tezza's RX-8800 case should be treated more gently with a lower concentration of H2O2, so that the risk of blooming is minimised. Simply put, what we are trying to do is camouflage it as we lighten the case colour, as once it's oxidised, there isn't a lot you can do because carbon will bond more strongly to oxygen than bromine does. It's happened, we can't reverse it, so the best thing that we can do is not make it worse.
 
Lorne said:
Or, maybe you or me.
Click to expand...

LOL. Yes, I'd love to do more experimentation but with a full time job and interests OTHER than vintage computing which all compete for my spare(?) time it's not possible to dabble right now. What with having to repair a vintage computer everytime I switch it on (!), working out how to use and EPROM programmer and website/blog maintenance, the VC weekly time allocation is fully booked!

I'm sure I can rely on you to forge ahead in the name of scientific endeavour Lorne :)

Tez
 
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Well, I've got the shell from an Apple 800K floppy drive sitting in a batch made from 12% H2O2, original Oxy Clean, and arrowroot, since I couldn't find Xanthan gum in town. I'd had it out in the sunlight, but it's very cold here at the time, and the solution started to get a skim of ice later in the day, so it's currently on the kitchen table with a small blacklight tube over the glass dish it's in...before and after pictures to follow!
 
Someone earlier posted about Apple plastics being more sensitive to the H2O2 concentration, I would recommend just sticking with the lower concentration with a longer "soak" time in the solution with the UV.

A few people including myself have had much success with the plain ol Wal-Mart 99cent 3% concentration bottle with mostly water solution. I'm not sure the higher solution is really needed except maybe extreme situations or lack of patience, which seem to have undesired effects.
 
I'd noticed the complaints about Apple plastics as well. That's why I'm starting with the 800K drive -- it's very yellow, and it's got the name of the school it was used in engraved permanently in the top. If it works well, I'm going to treat the case of my Mac Classic II, its mouse and keyboard, and the front of my Leading Edge Model D's case.

Since I got the jumbo container of Oxy-Clean, I'll pick up a bottle of 3% H2O2 at the store. I've got plenty of yellowed hardware, and it doesn't take much time to apply the solution. It'd be great if I could use the cheaper 3% stuff...doesn't matter if it takes longer, if it costs 1/5 the price!
 
When we were developing this method, members used concentrations of H2O2 from 3% to 30%. The optimum range is between 10 to 15% for an effective treatment, whilst minimising the risk of blooming and getting the task completed relatively quickly.

There's nothing wrong in a 'low and slow' approach, it just takes longer that's all. It took 20+ years to get that colour, a few extra hours or days won't hurt.

The main problem is that some people expect instant results from this; I suppose that's the legacy of the 'Playstation Generation', in that if gratification isn't instant, it doesn't work and they get bored....I must be getting old....
 
I've been doing a little de-yellowing lately, and something really weird is occurring, that has never happened before.

I mix the paste version as I always have, I apply it to the piece, it starts its usual foaming, and everything is as it always has been.
After a couple hours, I reapply it (without washing the original paste off), again as I have always done, and it's still fine.
A couple hours later, the paste turns to liquid and just runs off the part.
No more foaming, no nothing.
Subsequent re-applications don't foam either - they just turn into liquid as well.
I've tried this outside in the sun, and inside under the UV lights - the same thing happens no matter where I do it.
I'm thinking my H2O2 could be spent, although I don't know why it would work fine for the first couple hours though. I've had this H2O2 for about three months, but that's never been a problem before.
I'm also thinking maybe the shelf life of the Oxy powder is up. I've had that since we started this stuff (two years?). But again, why does it work for the first couple hours?
I'm going to get some new Oxy power, and some new H2O2, and see if that gets rid of the problem.

Meanwhile, has anyone else had this problem?
Does the Oxy powder or H2O2 have a shelf life that would reduce its working life after an initial period of time?
Any ideas?
 
Have you stored the Oxy in a cool, dry place? I just had a look at my can of Vanish. I bought it late last summer, and it has a date stamp 05 04 09 which I believe means it was packaged either on April 5 or May 4 last year. There is no obvious best before-dates on the can, and upon checking the manufacturer's homepage, I couldn't find any such information neither. Possibly a little of the air humidity escapes into the can everytime you open it and starts a very small chemical process to exhaust the powder, but Merlin would be better suited to comment on that.
 
It has been stored (indoors at 72 F, in a dark cupboard) in its original plastic tub which looks like it seals OK.
I've picked up the new Oxy and H2O2, so I'll see what happens.
Another thought that's been running through my mind is that maybe there's something on the plastic parts, that's stopping the process.
I've never run into that before though.
My money's on bad H2O2 or bad Oxy.
 
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