Where Does the Wax Go When You Burn a Candle?

You know that candle wax burns down and disappears whenever you light a candle. But where exactly does that wax go, and are you breathing it in? Today, we’re delving into the science of burning soy wax candles to learn about combustion reactions and discover where wax goes when you burn a candle. We also explain why incomplete combustion reactions can cause your candle to smoke and explore what the colors of a candle flame mean.

aromatic candles burn

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Where Does the Wax Go When You Burn a Candle?

No matter what type of wax your candle is made of, it’s essentially composed of hydrogen and carbon atoms, aka hydrocarbons. When you light the wick, the wax heats up until it melts and then is soaked up by the wick. The melted wax acts as a fuel to keep the candle burning.

Specifically, the heat of the flame turns the wax from a solid to a liquid, and then a liquid to a gas by breaking down the hydrocarbons into separate molecules of hydrogen and oxygen. Once the wax has been vaporized, the hydrogen and carbon molecules are pulled up into the flame. While there, they interact with the oxygen in the air into heat, light, water vapor and carbon dioxide. About 25 percent of the energy created by the combustion reaction is given off as heat. This is enough heat to melt more wax and keep the combustion reaction going until you blow out the candle or the wick burns down.

aerial view candles burning

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Why Does the Candle Flame Stutter or Smoke?

Sometimes, the combustion reaction doesn’t go perfectly, and the candle gets either too much or too little fuel or air, resulting in incomplete combustion. This incomplete combustion can cause the flame to stutter or soot to form. This is more common right after you light the candle, while the combustion reaction is still stabilizing. After a few minutes, the candle flame will usually begin to burn steadily.

However, if the candle flame still continues to stutter or smoke, you should check the candle to make sure it’s burning properly. If the wick is too long, the candle will soak up too much fuel (i.e., melted wax) which is why you should always trim the wick down to ¼-inch each time before burning. Take care to keep the candle flame away from drafts and gusts, which will also cause it to burn unevenly.

If you’re worried about breathing in candle wax, don’t be. The vaporized wax exists only right around the candle flame and quickly dissipates once the candle is extinguished. That being said, you should take the steps outlined above to ensure that the candle flame burns cleanly and doesn’t create too much soot, which can be unpleasant to breathe in.

single candle burns in dark room

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What Else Can a Candle Flame Tell Us About the Combustion Reaction?

At the base of the flame, you will find a blue area where the hydrocarbons vaporize into their component particles. This area is very rich in oxygen, and as the hydrogen separates, it interacts with the oxygen to form water vapor. Meanwhile, some of the carbon burns to create carbon dioxide.

The next area of the flame is a dark orange-brown color and relatively low in oxygen. In this area, carbon continues to break down and forms hardened particles to create soot. The next section of the flame is the yellow color we traditionally associate with candle flames. In this part, soot formation continues until the particles ignite.

If you look closely, you’ll notice that the candle flame has a thin blue halo. This blue edge is where the flame makes contact with the oxygen in the surrounding air and is the hottest part of the flame. Just like the base of the flame, the blue color comes from the presence of oxygen.

As the candle burns, hot air moves up the flame and cooler, oxygen-rich air rushes in at the base to replace it. This continuous cycle of moving air is what gives a candle flame its elongated shape and makes it point up. Without gravity, hot air doesn’t rise. Candle flames are spherical and mostly blue.

Candles are very simple devices, but the science between them is fascinating. To learn more about candles and making the most of them, check out our guide that explains how to burn a candle all the way down. The next time you light a candle, you’ll have a new appreciation for the science behind the illumination!