How do candles work?
Did you ever wonder how and why a candle actually burns? Why is it that a tiny piece of wick, that would normally turn into ashes in a few seconds if it wasn't at the heart of a paraffin block, can sustain a flame for hours and hours? Why won't paraffin burn without a wick?
Candles have take nsuch a place in our household universe that we don't even wonder how they burn anymore.
And yet, the process that keeps the flame burning is such an interesting and fascinating one!
Two main components work together in a candle:
The wick needs to be naturally absorbent, like a towel, or it needs to have a strong capillary action (as in glass fiber wicks used in oil lamps).
If you buy a length of un-waxed wick (see article "Why and how prime your wicks?") at a craft store and play with it, you will find that it feels like soft string and absorbs water very well. This absorbency is important in a candle because the wick needs to absorb liquid wax and move it upward while the candle is burning.
Paraffin wax (see the related article) is a heavy hydrocarbon that comes from crude oil.
When you light a candle, you melt the wax in and near the wick. The wick absorbs the liquid wax and pulls it upward. The heat of the flame vaporizes the wax, and it is the wax vapor that burns.
You can prove that it is wax vapor, rather than liquid wax, that is burning with two experiments:
The reason the wick does not burn is because the vaporizing wax cools the exposed wick and protects it. You may have seen the camping trick of boiling water in a paper cup. The cup does not burn because the water inside cools it. The liquid wax does the same thing for the wick.
Paraffin wax will burn on its own (see article "Safety first" about this topic), but it is like cooking oil, motor oil and coal in that you have to get it very hot for combustion to begin. This is what the miracle of candles is all about: only the tiny amount of wax on the wick is hot enough to vaporize and burn!