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This question is related to How do I change the color of a brick? and the exact opposite of How to minimise or remove sun-stains/fading from blocks?

Is it feasible to artificially age bricks in sunlight to get new colours? For example, I noticed that white bricks turn into various shades of off-white.

Are there any unwanted side effects of doing this, for example, bricks becoming fragile?

How long would the process take in general, if I put them outside all day in a reflective box?

Finally, is there a chart which shows which colours turn into what?

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Interesting, but somehow I don't think anyone has ever been perverse enough to study this thoroughly. –  Joubarc Apr 14 '13 at 11:05
    
I admit it sounds perverse, but I got the idea from the observation that white bricks are much more plentiful and varied compared to bricks of earthy colours — and yellow is a terrible approximation of skin tones! –  Gnubie Apr 15 '13 at 12:51
    
Or even turn bley to old grey :) –  Gnubie Apr 15 '13 at 12:54
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2 Answers

up vote 7 down vote accepted

In general the colors would take on a yellowish hue. The colors that are most damaged by sunlight are white and blue. White can turn all the way to dark tan, and blue will take on an ugly yellowish color. On the other hand red would fade into pink. But again; the sun does damage the bricks. They will turn brittle and somewhat powdery, like all plastics do.

If you want to change the color of LEGO bricks I recommend vinyl-dye that fuses with the plastic so there is no build-up and it won't scratch off easily. There is a limited color choice, but this is an excellent way to change the color if you really have to. My favorite brand is Plasti-kote Vinyl Color available at auto-supply stores. Quite expensive though and hard to find. Another brand is Krylon Fusion for Plastic, readily available at Wal-Mart and other places. The fusing is not nearly as good as with Plasti-kote, but it is still quite durable. The price is better and there are more color choices.

Another method would be using RIT dye (use the powdered form not the liquid), but I don't like this method as much because although the colors can turn out nice (they are pastel colors - kind of like what you find in LEGO Friends sets), but they do fade with age.

If you want to try the sun-method, just place outside some cheap elements and you will see what happens. Please note that the colors will continue to turn darker (in the case of white) even after you removed them from the sun. Kind of like how a sunburn continues to get worse even after you go in the shade...(c;

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Thanks, it looks like all colours tend towards yellow. I wonder what about yellow itself... As summer's coming, I'll do some experiments :) –  Gnubie Apr 15 '13 at 12:47
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TheBrickBlogger, can you re-dye bricks which have been previously dyed? –  Gnubie Apr 15 '13 at 12:57
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I'm surprised to see "white and blue" as most damaged colours - I would have spontaneously liste light gray rather than blue. No question on white, though. –  Joubarc Apr 16 '13 at 6:25
    
Gnubie, I have never tried re-dying an already dyed LEGO element - unless you count adding a second coat - which works fine. I don't see why it couldn't be done, but I suspect at some point there is going to be some build-up. –  TheBrickBlogger Apr 21 '13 at 17:14
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LEGO once used a brominated fire retardant in its ABS plastic. UV light causes bromine pairs in the compound to split and reconnect with oxygen atoms, taking on the brownish hue of elemental bromine.

Fire retardants containing bromine - known as PBDEs - are now considered toxic and many large companies have voluntarily stopped using them. The EU has banned the use of some bromine compounds in plastics. Some US states have also regulated them. I do not find any information online specifically about PBDEs in LEGO, but I believe LEGO may no longer use these compounds. I do not know when they might have stopped.

So if you want to intentionally give LEGO pieces that aged brown look, you will want to use older pieces sure to contain the bromine. Sunlight will work most quickly, but any UV light will do.

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