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How Do Trick Candles Work?

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.

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History
The Secret World War II History Hidden in London's Fences

In South London, the remains of the UK’s World War II history are visible in an unlikely place—one that you might pass by regularly and never take a second look at. In a significant number of housing estates, the fences around the perimeter are actually upcycled medical stretchers from the war, as the design podcast 99% Invisible reports.

During the Blitz of 1940 and 1941, the UK’s Air Raid Precautions department worked to protect civilians from the bombings. The organization built 60,000 steel stretchers to carry injured people during attacks. The metal structures were designed to be easy to disinfect in case of a gas attack, but that design ended up making them perfect for reuse after the war.

Many London housing developments at the time had to remove their fences so that the metal could be used in the war effort, and once the war was over, they were looking to replace them. The London County Council came up with a solution that would benefit everyone: They repurposed the excess stretchers that the city no longer needed into residential railings.

You can tell a stretcher railing from a regular fence because of the curves in the poles at the top and bottom of the fence. They’re hand-holds, designed to make it easier to carry it.

Unfortunately, decades of being exposed to the elements have left some of these historic artifacts in poor shape, and some housing estates have removed them due to high levels of degradation. The Stretcher Railing Society is currently working to preserve these heritage pieces of London infrastructure.

As of right now, though, there are plenty of stretchers you can still find on the streets. If you're in the London area, this handy Google map shows where you can find the historic fencing.

[h/t 99% Invisible]

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holidays
Custom-Design the Ugly Christmas Sweater of Your Dreams (or Nightmares)
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iStock

For those of you aspiring to be the worst dressed person at your family's holiday dinner, UglyChristmasSweater.com sells—you guessed it—ugly Christmas sweaters to seasonal revelers possessing a sense of irony. But the Michigan-based online retailer has elevated kitsch to new heights by offering a create-your-own-sweater tool on its website.

Simply visit the site's homepage, and click on the Sweater Customizer link. There, you'll be provided with a basic sweater template, which you can decorate with festive snowflakes, reindeer, and other designs in five different colors. If you're feeling really creative, you can even upload photos, logos, hand-drawn pictures, and/or text. After you approve and purchase a mock-up of the final design, you can purchase the final result (prices start at under $70). But you'd better act quickly: due to high demand, orders will take about two weeks plus shipping time to arrive.

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