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

[tezza]

I've observed something interesting happening to my Retr0Brighted computers. They seem to be returning to type.
http://www.classic-computers.org.nz/blo ... porary.htm

Anyone else notice this phenomena in their own Retr0Brighted machines?

[cjr]

Wow, interesting regression. I'll have to check mine but they were mostly done in 8-12 months ago so probably aren't anywhere near changing back yet.
It may well be worth posting in http://www.amibay.com/showthread.php?t=1480 and seeing what Merlin has to say.

[tezza]

Have you ever considered that Oxygen may be the cause ? could it be a process of oxidation (interaction between oxygen molecules and other substances)

Oh yes, it is formation of a co-ordinant bond with oxygen, 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 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.

The Retr0Bright wiki (http://retr0bright.wikispaces.com) does say even low levels from florescent lights is enough. I'd always assumed this was everyday exposure though.

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.

[SpidersWeb]

I liked the idea of a clear acrylic in the other thread - would have to experiment with that though - wouldn't want to change the appearance or make them super glossy.

[matsondawson]

I imagine even without UV the reaction would occur, just very slowly.
Maybe you could add a protective coating to the plastic that would prevent Oxygen ingress.
When you retrobrite does it leave behind any contaminants in the plastic that may react with oxygen also?
Also the retrobrite website mentions migration of the bromine to the surface, so maybe what you are seeing is untreated and unseen bromine migrating to the surface.

[tezza]

I liked the idea of a clear acrylic in the other thread - would have to experiment with that though - wouldn't want to change the appearance or make them super glossy.

Yes, that is the risk. It would be great to do some trials though although waiting for months (years!) to see if yellowing comes back means they would be long term projects.

[tezza]

When you retrobrite does it leave behind any contaminants in the plastic that may react with oxygen also?

One wonders. The retr0Bright mixture can be made up several ways and contains more things than just H2O2. There is laundry activator and also the sticker, both which would contain various substances, presumably inert but maybe not.

Also the retrobrite website mentions migration of the bromine to the surface, so maybe what you are seeing is untreated and unseen bromine migrating to the surface.

I'm sure that's what we are seeing. My surprise was that this was happening under very low UV/light exposure. The re-yellowing occurred only on surfaces that had been yellowed before though (and treated with Retr0Bright). For example, the inside of the cases (which are also exposed to oxygen) are not yellowed at all.

[matsondawson]

Also the retrobrite website mentions migration of the bromine to the surface, so maybe what you are seeing is untreated and unseen bromine migrating to the surface.

I'm sure that's what we are seeing. My surprise was that this was happening under very low UV/light exposure.

No, I mean the bromines are already broken down inside the case from previous exposure and not visible as they haven't migrated to the surface yet.
The migration wouldn't require UV light. That would explain why it happens in previously affected places.
If that is true then it seems retrobrite could never work for long periods.
Maybe someone could crack a retrobrited case in half for a cross section and have a look with a microscope.

[tezza]

No, I mean the bromines are already broken down inside the case from previous exposure and not visible as they haven't migrated to the surface yet.
The migration wouldn't require UV light. That would explain why it happens in previously affected places.
If that is true then it seems retrobrite could never work for long periods.
Maybe someone could crack a retrobrited case in half for a cross section and have a look with a microscope.

Yes, that is a hypothesis I came to also Matt, when I was reflecting on the problem on the VCF just now. This fits all the evidence. Retr0Bright is only skin deep and if there are preformed molecules further down, they may rise to the surface. And it's unlikely that a sealant or UV protection would prevent this.

[matsondawson]

Ah yes, just so others can follow your VCF post.
http://www.vintage-computer.com/vcforum/showthread.php?35227-Retr0Bright-Does-re-yellowing-occur-even-in-the-absence-of-UV-light

It would be sad if that's the deal as I'd love new looking machines.
What would be even more sad is that when you buy from ebay etc, you wouldn't know if it were retrobrite or just in good condition!

[matsondawson]

On another thought, I wonder if heating the plastic up and doing the treatment over a much longer period (like days) with weaker solution, would cause those BR's to come to the surface. Or alternatively treating the plastic (not coating it) to be hardened in some way that would prevent BR from egressing.

[tezza]

Thanks for the pic, MachineCoder

Good points Matt. Someone needs to get a chemisty honours student onto this.

[Carcenomy]

Some of these cases have taken decades to yellow, my question is if yours have yellowed like this in four years in darkness, how much more would they have yellowed in a normally lit room? Is it a constant level of yellowing regardless of exposure?

[tezza]

Some of these cases have taken decades to yellow, my question is if yours have yellowed like this in four years in darkness, how much more would they have yellowed in a normally lit room? Is it a constant level of yellowing regardless of exposure?

Yes, I don't think light plays a factor in this case. The bromide molecules causing the yellowing now were formed when the unit first yellowed. It's just they were deeper than the surface layer so Retr0Bright didn't deal to them. But you couldn't see them hence it looked like all the yellowing was gone. However, over time those deep degraded bromides made their way to the surface and lo and behold the surface was yellow again. Light wasn't needed or UV. Heat probably helped their progress as the computer room gets pretty hot in summer.

This is what I think happened, and it seems to fit what is known about yellowing and how those bromides behave in plastics.

The more yellowed a case is, the deeper those bromides probably are so the more like the case is to regress after retr0brighting. If the theory is right, another session of Retr0bright should make the cases white again....for a while. Then you might have to do it again...and again. However if you kept the case out of the sun/light so there was no NEW Bromide degradation then eventually all the bromides that formed in that initial yellowing might be out of the case, and it then might be permanent.

[Kitch]

Would that mean once all the Bromide had degraded the case would now be flammable?