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

  1. #1

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

    As some of you know, I've done a bit of Retr0Brighting in my time.

    Many of my treated cases and plastic bits are regressing, even in the apparent absence of UV light. I thought this was an interesting find, so wrote it up. See:
    http://www.classic-computers.org.nz/...-temporary.htm

    I'd be interested to know if anyone else has experienced this phenomena.

    Tez
    ------------------------------------------------
    My vintage collection: https://classic-computers.org.nz/collection/
    My vintage activities blog: https://www.classic-computers.org.nz/blog/
    Twitter: @classiccomputNZ ; YouTube Videos: (click here)


  2. #2

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    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!

  3. #3
    Join Date
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    I thought I had read that the yellowing was caused by the oxidation of the flame retardant in the plastic?

  4. #4

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    Quote Originally Posted by arrow_runner View Post
    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
    ------------------------------------------------
    My vintage collection: https://classic-computers.org.nz/collection/
    My vintage activities blog: https://www.classic-computers.org.nz/blog/
    Twitter: @classiccomputNZ ; YouTube Videos: (click here)


  5. #5

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    Quote Originally Posted by tezza View Post
    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
    ------------------------------------------------
    My vintage collection: https://classic-computers.org.nz/collection/
    My vintage activities blog: https://www.classic-computers.org.nz/blog/
    Twitter: @classiccomputNZ ; YouTube Videos: (click here)


  6. #6
    Join Date
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    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.
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

  7. #7

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    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.

  8. #8

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    By the looks of things, retrobrite was a waste of time.
    GEEKS WITH A GRUDGE!

  9. #9

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    For solid areas without any decals on them, why not just paint the plastic the desired color?

  10. #10

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    Quote Originally Posted by Great Hierophant View Post
    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.

    Quote Originally Posted by Great Hierophant View Post
    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
    ------------------------------------------------
    My vintage collection: https://classic-computers.org.nz/collection/
    My vintage activities blog: https://www.classic-computers.org.nz/blog/
    Twitter: @classiccomputNZ ; YouTube Videos: (click here)


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