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We’ve written before about Retr0brite, a technique that originated among vintage computer/electronics enthusiasts for restoring original factory case colors after years of weathering and yellowing. As it happens, the same technique can be used to restore old, yellowed Lego elements, and there is in fact an entire site dedicated to the method, which involves making a gel from 11% hydrogen peroxide, glycerine, vegetable gum, and a touch of sodium percarbonate (OxiClean). The gel is liberally applied to the yellowed plastic and exposed to a strong UV light source, e.g. sunlight, over the course of a couple days.

Turns out the yellowing of old ABS plastic is due to degradation of bromine-containing fire retardants which are added to the plastic during manufacture, which release elemental bromine, causing the yellow color. Shining UV light on the gel accelerates the decomposition of the fragile oxygen-oxygen bond in the peroxides it contains, generating reactive hydroxyl radicals which scavenge the free or loosely-bound bromine in the plastic that causes discoloration.

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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Comments

  1. tueksta.wordpress.com says:

    It disturbs me that toys for kids release elemental bromine, as its quite hazardous. Any facts on dangers of old toys containing chemicals?

  2. Sean Michael Ragan says:

    …I think most of it stays in the plastic, coordinated with oxygen atoms in the polymer. Even if some of it does get out, the potential exposure to bromine from handling old plastics is trivial compared to, say, drinking orange soda or other product containing brominated vegetable oil. Here’s a case of bromine poisoning from drinking a gallon a day of BVO-containing soda:

    http://informahealthcare.com/doi/abs/10.3109/15563659709001219?journalCode=ctx

  3. 8-bit Geek says:

    Not sure why the before and after is posted since it is obviously a different physical part. The tool marks in the middle on the right are missing on the after part, as well as the missing chunks of plastic on the middle left.

    1. vrandy.myopenid.com says:

      Nah, the marks are still there. Contrast is different, but if you zoom in and look really careful, they’re there.

  4. volkemon says:

    @8-bit Geek-

    I think that the different flash angles highlight the piece to create that effect. Look how the shadows created by the ‘posts’ shift.

    Neat process, and one I was not aware of.

  5. https://login.launchpad.net/+id/LNHAtsT says:

    Neat, I need to use this on my white bricks from my youth, all yellowed to different degrees.

    While we’re on the subject of Lego, anyone have a good method for cleaning a large bulk of Lego easily? I’m tempted to pick up a lot of used bricks and I’d like to clean them up before they go into the collection.