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Thread: Retrobright by sun only

  1. #21
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    I think some of the problem is people getting rid of the yellow long enough to sell it on ebay for more money then a yellowed model would get.

    One of my old XT PCs made by Kaypro had a yellowed face and the case was starting to rust so I just painted both and it turned out ok (you need paint made for plastic and it seems to take a long time to dry).

    Anyway the faceplace was brittle and the parts you screw to the metal case were snapping a decade ago when I got it. Retrobright would have just made things worse and I have no intention of selling it anyway (and it would probably crack if I shipped it anyway).

    To be honest a simple wash with dish soap and water can lighten yellowed plastic quite a bit without making it more brittle.

    What we need is a clear spray on compound that blocks UV and keeps the plastic from scratching and falling apart. Pretty much to keep things from getting worse. Or just a removable paint that does the same thing.
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  2. #22

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    Quote Originally Posted by Unknown_K View Post
    What we need is a clear spray on compound that blocks UV
    UV light is not the problem; this is just still a very common misbelief. If you put a piece of yellowed plastic in the sun outside, it's the UV light that actually removes the yellowing. And inside your house, you have pretty much no UV light at all. Stuff is yellowing anyway. It's a chemical process that just happens, driven by heat (the colder you store something, the slower it yellows - but it still will yellow).

  3. #23
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    I agree. I am not sure I believe UV is the yellowing culprit. UV is certainly used in retrobrighting but the yellowing may just be the progressive degradation of the plastic. What we need to find is a way to halt or slow the process as my first retrobright work is already yellowing and all of it is only susceptible to ambient light, nothing in direct sunlight.

  4. #24

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    You can't stop it, unless you find a way to freeze time. It's like trying to stop fruits from rot. You can slow it down, but never stop it from happening.

    The stuff I retrobrighted in the past has re-yellowed much worse than it was before retrobrighting, so I stopped doing it at all. Now I limit myself to give everything a good clean and take the yellowing as patina.

  5. #25
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    Guess you never heard of Irradiated food: https://www.fda.gov/food/buy-store-s...-you-need-know

    There is always a means, we just haven't figured it out yet. That goes with everything.

    Nothing I retrobrighted is anything near what it was when I gave it the treatment. Its just enough to be bothersome to look at.

  6. #26
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    ABS plastic turns yellow because of chemical reactions involving the “B”, butadiene, and retrobrite in no way reverses it. The reaction is inevitable and its speed is more likely to be influenced by heat than UV. (Glass blocks a lot of UV, but plenty of infrared, IE, heat, makes it through, which may well explain the “the side facing the window is browner” phenomenon.) The same reaction that produces the browning is also what makes the plastic more brittle.

    Regarding the idea of just leaving something in the sun to bleach it, well, no, I’m not doing that. I can certainly attest that it’s an effective way to bleach the color out of plastic based on what happens to toys the kids have left out over the summer, but those same toys also crumble to dust remarkably easily after that treatment. Some plastics resist solar bombardment better than others, that’s true, but it’s certainly pretty obvious that bleaching old computer cases isn’t likely to *improve* their structural integrity.
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  7. #27
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    Some plastics will never be the exact same color/shade they were then they were new, no matter what you do. A while back I had tried to whiten up a faceplate that was supposed to be a light gray, but it retained a brown tint even after lightning up quite a bit. On another item, a broken piece reviled the plastic was yellowed all the way through, and whitening treatments often only change an outer layer.

    In another case, the yellowing was so uneven that I probably would have had to reduce it to dust before it was an even white. That case just called for spray paint, although it is annoying that it is difficult to find good beige-ish shades.

    I've also had a few items yellow a bit, that I know as a fact have been stored inside in cool areas with minimal light their entire lives.

    I've started to just settle for lightning up yellowed items only a little bit so they don't look like they just came out of a hot warehouse.

  8. #28
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    Quote Originally Posted by Timo W. View Post
    The stuff I retrobrighted in the past has re-yellowed much worse than it was before retrobrighting
    Quote Originally Posted by VERAULT View Post
    Nothing I retrobrighted is anything near what it was when I gave it the treatment.
    What timeframes are you both talking about? I'm just curious. I know Tezza's was something like 4 years before yellowing came back to the point where it was distracting.
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  9. #29
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    3 years and its just got enough yellow tinge to be disappointing. But by no means the taxi cab yellow alot of the parts were.

    I am also not leaving anything out in the SUN. I own a 1989 car as I have said many times and I can on the car and many older things I still own attest to the destructive nature of Sunlight on plastic. Plastic in the Sun just gets destroyed, its a bad idea.. Its basically slowly digesting the plastic.

  10. #30

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    I'm not trying to be the proverbial naysayer, but every time I see references to retrobrite or using UV radiation to whiten yellowed plastic, it makes my skin crawl.

    The problem is that both of these methods are long term destructive to the plastic surfaces because they are oxidizing agents. It will simply shorten the life of the plastic and it will crumble away in the long run, or the surface go powdery and break down.

    Correct me if I am wrong but my assumption was that as vintage restorers it was our responsibility to find methods to restore what was left and make it last longer.

    I have mentioned this on other posts, by far the better method to correct the yellowing is to re-coat the surface with a protective layer. But of course everyone's first thought is, what ? Paint, it will ruin everything and flake off.

    Well it will not if the right kind of paint is used, because it chemically reacts with the surface and etches its way into the surface in the minutes before it dries (yes minutes). It then creates a new plastic surface, just as durable and scratch resistant as the original surface, Plus you can select the shade of white or off white you require for a perfect match to the original. The paint that works in this mode for all vintage computer plastics is Holts Duplicolor, a fast drying automotive lacquer. Even if the original plastic surface was textured, it still works with a thin coat and the texture remains. When you scratch the surface you will find it has "becomes one" with the original material and doesn't sit as a layer waiting to flake off.

    I have used this fine spray paint to "protect and restore" yellowed video monitors such as the IBM5153, the Apple IIe monitor and more. Not only does it solve the issue with the appearance, rendering it to new condition, it also protects the old plastic from further harm by UV rays and other oxidizing agents.

    The monitor casing in the attached photo was restored this way, the original surface texture was retained.

    (Don't use any other type or brand of paint, there is only the one that etches and becomes one with the surface and is fast drying enough to work).

    I put some other images of the results with this type of paint on another thread, but it was largely ignored due to the notion that retrobrite was better, and paint would flake off, but retrobrite is not better (nor is UV bleaching), not for either the cosmetic result or the long term stability of the aging plastic.
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    Last edited by Hugo Holden; September 17th, 2020 at 05:12 AM.

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