Trick candles are candles which will reignite after they are blown out. They come in a range of shapes, sizes, and colors, although most of them are designed to be installed on birthday cakes. These candles can be used in essentially any situation where someone must blow candles out, but they should be used with caution so that a fire is not started.
When you blow out a regular candle, a small ember continues to burn in the wick for a moment. You may have noticed that a plume of smoke rises from a candle which is blown or snuffed out. The smoke is caused by the ignition of paraffin vapors rising from the candle as the ember dies out. The heat of the ember, however, is not enough to actually relight the wick, as paraffin requires a higher temperature to burn.
In trick candles, the wick is impregnated with something which will burn at a lower temperature, causing the candle to reignite. Magnesium is a popular choice for this application. When the candle is blown out, the magnesium ignites, causing the wick to start burning again. Often, a few sparks are thrown off in the process. These sparks are also what make the candles potentially hazardous, especially if they land on lightweight fabrics and paper. Make sure that the area around the trick candles is clear before lighting them, to reduce the risk of accidents.
Trick candles can be allowed to burn until they run out of fuel, but they also can be put out in an emergency situation. To put the candles out, they can be snuffed, totally cutting off the oxygen supply so that a fire cannot start, but you will need to keep the snuffer on for a moment to ensure that the ember is out. A more effective technique is dunking the candles in water, which will also cut off the oxygen. You may want to keep water handy when working with trick candles, just in case.
You may also want to consider your audience when purchasing trick candles. Some people appreciate the joke, while others, especially young children, do not. These candles be be frightening and upsetting, which puts a damper on the experience for everyone. If you do not know your intended victim well, you may want to check with a friend to ensure that the trick candles will be received with good humor.