Why are trick candle flames so impossible to blow out?

It’s a familiar scene at birthday parties and other celebrations: The guest of honor blows out the candles on his or her birthday cake. Thin ribbons of smoke escape from the wicks, signaling the guests to clap and cheer.

But wait! The wicks begin to glow a fiery red. They flicker, and suddenly the flames reappear. Looking bemused, the birthday boy or girl tries to blow out the candles—again and again, much to the delight of the onlookers.

Trick candles, also known as magic candles, can add a flash of spontaneity to any party. The chemistry that allows these candles to repeatedly reignite turns out to be surprisingly simple.

Candle wax is typically made from paraffin hydrocarbons, and the wick is usually braided cotton treated with a chemical salt solution to prevent the wick from being destroyed too quickly by the flames, says Bob Nelson, director of fragrance development at Yankee Candle. “Wick manufacturers are secretive about the exact formulations they use,” he adds.

In a trick candle, magnesium powder is incorporated into the candle’s wick. Magnesium is a highly reactive metal when powdered or sliced thinly. It can ignite at temperatures as low as 800 ºF (430 ºC). When the flame is blown out, the hot embers from the wick ignite the magnesium powder, producing tiny sparks. This, in turn, ignites the vaporized paraffin hydrocarbons, which relights the wick. The magnesium found lower down in the wick doesn’t burn because it is protected by the paraffin. Magnesium powder is used in trick candles because it is flammable at a lower temperature than other pyrophoric metals such as aluminum or iron.

Trick candles are so simple to make that video instructions are readily available on YouTube and other video-sharing sites. But experts caution that the simple fun of these candles belies the dangers they pose. “We’re very concerned about these candles because of the potential fire hazard,” says Barbara Miller, a spokeswoman for the National Candle Association, in Washington, D.C. “People think the candles are done, so they take them out of the cake and throw them in the trash. Suddenly their trash is on fire.”

Miller recommends thoroughly extinguishing the candles by running them under water to cut off the candle’s oxygen supply. “When I use the candles, I douse them in water and set them in my sink for an hour or two before I put them in the trash,” she says.

Canada has banned the sale and advertisement of trick candles since 1977. Trick candles are currently legal in the U.S., and they are typically manufactured in Asia. “I think it would be very difficult to ban them here in the U.S.,” says Miller. “Of all of the issues that people are dealing with in product safety, trick candles are way down on the list. Our best bet is to continually try to educate consumers about the potential fire hazards of these candles.”

Information on when trick candles were invented and by whom is difficult to track down, but C&EN found several patents related to the basic principle. For example, in a 1983 Japanese patent titled “Self-Ignited Candle,” inventor Toshio Takahashi describes a candle fuse made of aluminum, magnesium, or iron, or an alloy of those metals. In a 2003 U.S. patent, Earl M. Stenger describes his invention of a wind-resistant candle that contains wick fibers made of a pyrophoric material such as magnesium or a magnesium-aluminum blend.

Inventors continue to experiment with novelty candles, including those that burn with colored flames. These candles are typically made by incorporating metal salts into the candles, but so far the commercial potential of these candles has been limited. Nelson says that Yankee Candle had looked into colored-flame candles several years ago, but there were issues with proper burning in the prototypes they examined.

Ron Newman, an independent consultant on home fragrance product formulations at Newman Anouvair, says there is a lack of data on the toxicity of metal oxide emissions from colored-flame candles, which has given pause to some companies considering using the colorful technology in their products. “This is really an unknown area of emissions,” Newman says.

As for trick candles, the novelty never seems to wear off. At parties everywhere, the candles, like their flames, just keep coming back.

UPDATE: This article was modified on March 29, 2017 to refresh its information and data.