When I first started candlemaking, I had almost no understanding of how candles work. Where does the wax go? When a candle burns, what changes take place? Since it seemed like straight candle magic, I decided to take a deeper dive into the science behind how a candle burns.
When you light a candle wick, the heat from the flame melts the wax immediately surrounding it. The wick is made of an absorbent material (usually cotton, but wood wicks are becoming popular) which then soaks up the melted wax and pulls it upwards towards the flame.
This ability of liquid to flow in opposition to gravity is called capillary action (other materials, like glass fiber, may also be used as a candle wick if they have strong enough capillary action). Think about when you've left a towel draped over a sink or bathtub & it's left touching water - all of that moisture will be drawn upwards into the towel. Same principle goes for the candle wick.
As the melted wax in the wick moves upward and reaches the flame, combustion occurs. In this chemical reaction, the melted wax molecules interact with the oxygen molecules in the air and are broken down into carbon dioxide, water (which is released as invisible steam) and some small unburned carbon particles (smoke & soot). Basically, the wax becomes vaporized. The energy from this reaction is the heat & light you see in the candle flame.
As the candle burns down, the wick continues to pull up more & more melted wax, continuing the chemical reaction until either the flame is put out or the wax is gone. The wax itself can be burned without a wick, but only at an extremely high temperature, making it more likely to simply melt when exposed to flame. In a candle, the wick keeps the melted wax in the heat of the flame long enough for it to become vaporized & ignite - continuing the combustion process.
The wick itself curves outward towards the edge of the flame, where the oxygen-rich air causes the intensest heat. This causes the wick to incinerate & burn away. Meanwhile, the vaporizing wax keeps the rest of the wick cool enough that it doesn't burn. The closer to the center of the candle flame, the cooler the temperature will be.
In summary, heat from the flame melts the wax. The melted wax soaks into the wick & is pulled upwards into the flame. The combustion process vaporizes the wax & continues until the flame is put out or the wax is gone.
Voila - a little candle magic, brought to you by science.