Imagine a birthday party. Here is his cake and it is beautiful. It comes complete with 46 candles, all ablaze. Now it is time to blown the candles out. He huffs, and he puffs… and then the agony – they are trick candles. He can’t blow them out, because they relight themselves automatically.

If you have 46 of those trick candles on a cake, there is an unforeseen problem. It becomes a hazard to public safety, like this:

In a more controlled situation (only 7 candles), you avoid the inferno:

By the way, the only way to put these candles out is to grab a cup of water. One by one pluck and dunk the candles.

It brings up a good question: How do these trick candles work? And what about normal candles? Candles are actually pretty amazing devices.

A candle has only two pieces: a solid fuel made of paraffin wax or beeswax, and a wick. But talk about something being greater than the sum of its parts. A block of wax by itself is pretty useless, and a wick by itself will burn in a few seconds. But when you put them together, you have something that will provide a source of steady light and heat for many hours.

The wick of a candle actually has two jobs. It is a pump and a vaporizer. When the wax melts, capillary action in the fibers of the wick pumps the liquid wax upward. There, the heat of the flame vaporizes the wax so it can burn. Meanwhile, the top of the candle forms a small cup that holds the liquid wax so it can enter the pump.

This brings up another question – what is paraffin wax? It is actually a hydrocarbon, just like gasoline or kerosene. In fact, paraffin wax comes from crude oil just like gasoline or kerosene do. The reason why paraffin wax is a solid while gasoline is a liquid has to do with the length of the carbon chains in the fuel. In gasoline, the carbon chains are eight carbons long. In kerosene, which is a little thicker and oilier, they are twelve carbons long. Paraffin wax has carbon chains 30 carbons long – long enough to solidify at room temperature.

The paraffin wax liquefies because of the heat of the flame, and the wick pumps the wax upwards into the flame. The wax then turns to a vapor that is quite flammable. To see how flammable the vapor is, try this experiment. Light a candle and, after it has been burning for a minute or two, blow it out. You will see a stream of white smoke rising from the wick. There is a tiny glowing ember in the wick, and it is hot enough to keep vaporizing the wax until the ember goes out.

That white smoke is actually paraffin wax vapor. If you touch a lit match to the vapor right after you blow out the candle, the flame will shoot down the stream like a fuse and relight the wick. You can light the stream as much as 12 inches away from the wick and the flame will travel down it to light the candle. It is a fun trick to show your friends.

Now you can see all the working parts in a normal candle. There is the cup of liquid wax at the base of the wick, the wick acting as a pump and vaporizer, and the wax vapor that is actually burning in the flame. The flame provides the heat to do the vaporizing as well as the heat to create the liquid in the cup. It’s genius.

So, how does a trick candle work? We need to add one more thing to the wick. We need something that the glowing ember can ignite, so that its ignition can relight the stream of vapor. That something is magnesium powder. The ember can light the specks of magnesium. If you carefully watch the wick of a trick candle, you can see the specks bursting in minuscule explosions of flame every few seconds. That little explosion is enough to light the vapor, which relights the wick. And the candle keeps burning.

The addition of that magnesium dust to the wick is all you need to create a trick candle. It’s simple, but quite effective. Try one at your next birthday party. One.

See also: How do trick birthday candles work?