Today is my birthday. While you're surfing mentalfloss.com, I'm home celebrating with single-malt scotch and Rock Band. Wish you were here. In honor of my special day, here's the science behind the trick in trick candles, which I really hope aren't part of today's festivities, for they are cruel and unusual and prolong the wait for delicious cake.
A lit candle wick melts the paraffin wax near it, absorbs the liquid wax, and pulls it upward. The flame vaporizes the wax, the vapor burns and keeps the flame lit, allowing the cycle to continue. When you blow out a regular candle, you might notice the little wisp of smoke that rises from the wick. That's a last little bit of paraffin that's been vaporized by the dying ember of the wick, but didn't ignite because the ember isn't hot enough.
The trick to a re-lighting candle, then, is getting enough heat going to ignite the escaping vapor and bring the flame back to life. The folks who don't want you to eat your cake and make these candles usually turn to magnesium for the job. Magnesium, the ninth most abundant element in the universe by mass, is an alkaline earth metal that's highly flammable and ignites at temperatures as low as 800 degrees F (430 degrees C) when powdered or shaved into thin strips. Powered magnesium is put inside the wick, where it's kept cool and shielded from oxygen by the liquid wax. When the candle is blown out, the wick's ember ignites the magnesium "“ if you watch closely, you can see little bits of magnesium sparking "“ which ignites the paraffin vapor and re-lights the candle. Magic!
The problem, of course, is getting the candles out once and for all when you get tired of games and want to eat (or if the cake bursts into flames). Trick candles need to be snuffed or dunked in a liquid to cut off the oxygen supply so the flame can't re-ignite. And no, you cannot use my scotch.
This question was suggested by my friend Paul. If you've got a burning question that you'd like to see answered here, shoot me an email at flossymatt (at) gmail.com. Twitter users can also make nice with me and ask me questions there. Be sure to give me your name and location (and a link, if you want) so I can give you a little shout out.