Subject:
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Re: Yellowness
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Newsgroups:
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lugnet.general
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Date:
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Mon, 5 Mar 2012 15:52:21 GMT
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Viewed:
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20706 times
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In lugnet.general, Sonnich Jensen wrote:
> even brick I bought at the time was now very yellow.
> [...]
> Is this a common thing?
Yep. I don't really understand all the chemistry going on there, but essentially
LEGO has a flame retardant in their ABS plastic which contains Bromine-- a
naturally yellow/brown color. So, when exposed to UV light (direct or indirect),
this can trigger a process by which the Bromine atoms break off from the flame
retardant, and form some other molecule (I assume Br2, but I don't know), which
makes the bricks appear yellowish.
Each color behaves differently, but this problem is most visible with white and
gray. Other colors may suffer from this to a certain extent (blue is probably
the next most noticeable).
By the same token, however, direct UV light can also REVERSE the process-- at
least to a degree. Again, the UV light breaks the bonds in the Br2 (or
whatever), and the Bromine can re-bond to the flame retardant.
You can also help speed up (and help guarantee) the reversal process with
something like Retr0Bright:
http://retr0bright.wikispaces.com/
DaveE
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Message is in Reply To:
 | | Yellowness
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| Hi I once built a large building in white, though not finished. It stands on a cupboard, at the other end of the window, hence not in the sun However, due to ... reasons I have not completed this for some 4+ years, but just lately I realised, that (...) (13 years ago, 5-Mar-12, to lugnet.general)
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