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Retr0Bright: Does re-yellowing occur even in the absence of UV light?

My Mac Plus got yellowed, even though it has spent nearly all its life since I got it in the mid-'90s in a dark corner of my basement, shielded from any direct light. And my Commodore 128 was the worst case of yellowing I ever experienced, even though it almost never left the cardboard box it was sitting in, totally blocked from any light!
 
I thought I had read that the yellowing was caused by the oxidation of the flame retardant in the plastic?

As far as I know it is, but I'd always assumed (maybe wrongly) that a reasonable amount of UV light was needed to facilitate this. Based on what's happened it may be that very little UV (if any) is needed. I too have heard stories about people putting white cases into dark storage and years later bringing them out yellow. In the case of my Retr0Brighted cases....just a few days exposure per year under florescents (i.e. the time I had the computers out of the box to play with or test) seemed to be all that was needed.

Merlin, in his writeup in the Retr0Bright wiki does say even low levels from florescent lights is enough. I'd always assumed this was everyday exposure though.

There is something more puzzling. Let's assume yellowing can occur in the absence of much (or any) UV light. Why then are those cord markings on the Apple IIe and Vic 20 reappearing? You would have expected any further yellowing of my cases, even with low levels of UV, to be consistent across the case surface now the cords are not there. All surfaces would be exposed to equal amount of oxygen or brief light. However the cord impressions (which protected the plastic under them from initial yellowing) are re-appearing?

The question I have in my mind therefore is "do the changes in the chemical structure cause by the initial yellowing (OR perhaps the RetroBrighting itself) make the plastic MORE prone to future 2BR.O co-ordinant bonds or/and migration of these to the surface of the case (hence causing yellowing)? " Or is something else going on?

Whatever is happening, the practical implications are that even brief and very very low levels of UV seem to be enough to re-yellow retr0Brighted surfaces over time. There is not enough evidence in my case to say that UV is not needed AT ALL, as all the units had been exposed briefly a few times a year, to fluorescent light.

Tez
 
The question I have in my mind therefore is "do the changes in the chemical structure cause by the initial yellowing (OR perhaps the RetroBrighting itself) make the plastic MORE prone to future 2BR.O co-ordinant bonds or/and migration of these to the surface of the case (hence causing yellowing)? " Or is something else going on?

Just a further observation, I notice that the RX8000 case is yellowing quite evenly, even on the part that was initially protected from sunlight by a monitor stand. It is now more yellow that it was originally, although you can still make out the circle so the yellowing there hasn't progressed quite as much as the rest of the case.

Tez
 
Perhaps the cause of re-yellowing is not so UV light but a natural degradation or breakdown in the pigments or dyes used in these plastics. Even in the dark basement, the plastic is still exposed to oxygen or lack thereof, moisture (dank basements), low levels of radiation (closer to the earth), heat, cold, static electricity, smoke, dust, etc. Perhaps they accelerate the re-yellowing. Could the retro-bright agents be breaking down.
 
I do remember, when retrobright was first publicized, there was a recommendation to coat pieces with clear acrylic lacquer to seal it against oxygen and prevent re-yellowing. It was just a minor footnote, and thus never really came up in discussions much... but perhaps that little detail was a bit more important than it seemed to be at the time.
 
Perhaps the cause of re-yellowing is not so UV light but a natural degradation or breakdown in the pigments or dyes used in these plastics. Even in the dark basement, the plastic is still exposed to oxygen or lack thereof, moisture (dank basements), low levels of radiation (closer to the earth), heat, cold, static electricity, smoke, dust, etc. Perhaps they accelerate the re-yellowing.

Yes, but if it was natural degradation or breakdown (or just oxygen) the insides of these cases would also be yellowing. They are not. The insides are not yellowed at all. Only the areas that were originally yellowed (and also treated with Retr0Bright) are now re-yellowing.

Could the retro-bright agents be breaking down.

Well, if this yellowing is higher than it normally would be under the given light conditions then it's a result of the plastic already being damaged somehow by either the initial yellowing, or the Retr0Bright itself. I'm thinking it could be the former. Presumably a yellowed case has lots of these small 2BR.O co-ordinate bond molecules throughout the plastic. However Retr0Brighting only deals with the very top layer, and if they are already pre-formed lower down, all they need to do is find their way to the surface? (in which case would sealing against Oxygen really help anyway?)

Does this sound a reasonable hypothesis? Any plastics chemists out there?

Tez
 
Well, if this yellowing is higher than it normally would be under the given light conditions then it's a result of the plastic already being damaged somehow by either the initial yellowing, or the Retr0Bright itself. I'm thinking it could be the former. Presumably a yellowed case has lots of these small 2BR.O co-ordinate bond molecules throughout the plastic. However Retr0Brighting only deals with the very top layer, and if they are already pre-formed lower down, all they need to do is find their way to the surface? (in which case would sealing against Oxygen really help anyway?)

The more I reflect on this, the more it fits all the evidence.

Here is the hypothesis. The original damage from light causes degraded or free bromides throughout the case from the fire retardants. Retr0Bright only takes these away from the top layer. However these bromides can migrate fairly freely through the polymer. They don't need light to do this. Migration is probably accelerated in hot conditions. They migrate to the top and within a few years the surface is yellowed again.

If this hypothesis is correct then a UV sealant will not protect the case. Or any sealant maybe. Unless pre-formed bromides from previous light damage can be stopped from migrating to the surface (and I don't know how you would do that) Retr0Bright is only ever going to be temporary.

Sound logical?

Tez
 
This is disappointing news. I was going to give Retr0Bright a try on one of my IIes. Now, I'm inclined to spray paint it, as suggested by vwestlife. I'd appreciate any suggestions regarding preparation and paint. Or would you prefer that I pursue this in another thread?
 
This is disappointing news. I was going to give Retr0Bright a try on one of my IIes. Now, I'm inclined to spray paint it, as suggested by vwestlife. I'd appreciate any suggestions regarding preparation and paint. Or would you prefer that I pursue this in another thread?
Indeed. Disappointing.

Bear in mind that the theory above (pre-existing bromines from the original damage migrating to the surface) is only a theory. It would need testing and research to prove or disprove. It does seem to fit with what we know about yellowing and my results though.

Tez
 
Yes, but if it was natural degradation or breakdown (or just oxygen) the insides of these cases would also be yellowing. They are not. The insides are not yellowed at all. Only the areas that were originally yellowed (and also treated with Retr0Bright) are now re-yellowing.

I would assume that the inside of cases see a lot less oxygen movement.

Have you presented your findings to the chemist(s) who originally came up with retr0bright?
 
I would assume that the inside of cases see a lot less oxygen movement.

Have you presented your findings to the chemist(s) who originally came up with retr0bright?

Well, I'm not so sure. 99.9% of the time these computers were sitting deep in buried boxes. I wouldn't imagine there would be any oxygen movement to speak of, either in or out.

Yes, I did send a PM to Merlin this morning. Merlin introduced Retr0Bright to VC, and did most of the work on the wiki. I think he is a chemist. I'd love to hear a chemists opinion on the theory and also like to hear about the status of machines that were Retr0Brighted about the same time mine were.

Tez
 
Well, I must say that this is only fitting.
I've been away for what seems like a year (golfing my brains out & a bit of work too) and what do I come back to see on the New Threads link, but a post about RetroBrite.
That figures. :)

I dunno Tez.
Maybe they've got bum hydrogen peroxide in NZ?
I just went and looked at my Osborne 1 (grey case), and the three Televido 9xx's I did, and I don't know what to tell you.
Mine all look like they did after I did the treatment.
I see no regression at all.

You're not storing them in an attic, and then exhausting a smoking room or the kitchen fan exhaust up into the attic are you?

I forget - are you on the coast (near salt air) or inland.
Just wondering if something else in the climate may cause the earlier regression.

Maybe they just yellow more in the southern hemisphere.
Time for a move?

It's already fun to be back.
 
Mine all look like they did after I did the treatment. I see no regression at all.
Hi Lorne,

Long time no see (-: Well, that's interesting. Thanks for posting. It's good to see the phenomena is not universal.

It makes me wonder if there are all kinds of subtleties involved...the exact type of plastic, etc. Different plastics have different tendencies towards yellowing so it would be no surprise if it was also the case in reverse. Bromines travel better/quicker up through some cases than others perhaps.

Were yours stored in a place that got hot occasionally? My loft/shack does during the summer (29-30 deg). This would certainly help mobility of molecules in plastics.

No climate affects. We are inland and pollution free. NZ does get high levels of natural UV BUT the Atari 130XE, to use an example, was buried in a closed box underneath three other boxes and I would have only got it out a maximum of three times for about 45 mins each time over the whole 4 years! Just long enough to check it and photograph it. Blinds would have been closed and it would have been under fluorescents only. And it's turned green again! I find it hard to believe such a small dose of light would cause that.

Would anything from exuding from the cardboard in cardboard boxes cause this? I did read somewhere that cardboard boxes can exude chemicals. They are in all different types of boxes mind you. The Lisa was unaffected (so far) and was the only one not in a box! Mind you, the others have two years on the Lisa. I don't think they were looking too bad after 2 years either.

Certainly it would be good for others to post their experiences. I'm really curious about this phenomena now.

Tez
 
Mine are all stored indoors - 72 F in the winter and 79 F max in the summer.

On the cardboard thing: my Osborne and the Televideo 910 are stored in their original 30 year old boxes. Are you storing yours in new cardboard boxes? Does cardboard exude forever or just when it's new? If it did any exuding, I'd bet the stuff they use for glue or bleaching of the cardboard is worse now than it used to be.
The other two Televideo's aren't stored in any boxes, and regularly get indirect sunlight.

I think we need Merlin's input here.
 
I think we need Merlin's input here.

Agree. At this stage we need the expert opinion of a plastics chemist to see if my hypothesis stacks up.

It would be good to get some more examples though to see if my result (or yours) is an exception. Surely we weren't the only two ppl in the VCF who Retr0Brighted stuff Lorne?? :)

Tez
 
Early 2011, I treated some items:

1. Microwave oven door - Retr0bright gel
2. CD-ROM case bezel - generic oxy cleaner from supermarket
3. Microsoft Mouse - generic oxy cleaner from supermarket

Re item 1. Retr0bright gel. The door has definitely regressed. It is now very patchy, half of the patches are one shade of yellow, and the balance of patches are a lighter shade of yellow. Two years ago, I never did completely get rid of the yellow, but I got the colour down to a very very light yellow, and patch-less, enough for me to put off buying another oven.
A comment I'll make is that it now looks like what it did part way through the treatment. Then there were patches, which seemed to tie in with the thickness of applied gel. I think it is what others named "blooming".

Re item 2. Generic oxy cleaner. I accidentally left the bezel in the solution for way too long and that slightly damaged the plastic. Looking at the bezel now, it hasn't regressed at all. Over the past two years, the CD-ROM drive has been stored in a book case with the bezel against the back wall of book case, and so little exposure to light.

Re item 3. Generic oxy cleaner. The mouse originally was very yellow. Unfortunately, that mouse was returned to my box of mice and I can't distinguish it from the other mice. The fact that none of my Microsoft mice are significantly yellow suggests that the subject mouse has not regressed. And if it has, it hasn't regressed by much. Over the past two years, my mouse box has been open and exposed to indirect sunlight (curtained room).

Of course, the above sample size is not statistically significant.
 
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