As candle lovers, we all know the beauty of a lit candle…the soft glow that can be emitted and the ambiance that a candle flame can provide. But just what happens when we strike that match and light the wick? Have you ever studied the flame? Being the candle geekaholic that I am, I most certainly have! If you look carefully at the flame, you’ll notice several colors – or zones. Before we study the zones, though, let’s cover the basics of how a candle burns.
How a candle burns
All wax is composed primarily of hydrogen and carbon, bound together as hydrocarbons. That wax, or mass of hydrocarbons, is our fuel. Once the wick is lit, fire travels down the wick to find that fuel. As the wax melts, a pool of liquid is formed that is drawn up into the wick through a capillary action. Back down at the wax melt pool, the wax is being vaporized – the hydrocarbons are being broken down into hydrogen atoms and carbon atoms. These atoms are then drawn up into the fire and begin reacting with available oxygen from the surrounding air. This reaction (combustion) is able to create light, heat, water (when hydrogen combines with oxygen), and carbon dioxide (when carbon atoms combine with oxygen).
The flame is involved in three different processes: conduction, convection, and radiation.
- By conduction, more heat will travel down the wick and melt more of the wax on the surface.
- By convection, more oxygen is sucked in from the surrounding air and fed into the base of the flame.
- By radiation, rays of heat will be given off in all directions surrounding the flame.
The Candle Flame
Now that we’ve covered candle chemistry 101, light a wick and let’s look at the flame.
Innermost Zone: This is the area right at the base of the wick where it is very close to the wax melt pool. Here the wax is just beginning to melt and the hydrocarbons are being broken down. Hydrogen is released first, so it is the first to combine with the oxygen and water vapor is created. However, there is insufficient oxygen in this zone for complete combustion. This area is the least hot of all zones and is typically around 600 degrees Celsius.
Outermost Zone: Find the bluish part of your flame, which starts around the base and then you’ll see a thin, outer area that follows the flame up. That is considered the veil and it becomes lighter in color, almost white and invisible. This area is oxygen rich – there is more than enough oxygen here for complete combustion. This is the hottest part of the flame and temperatures are around 1400 degrees Celsius.
Middle Zone: This is the bright yellow area of the flame and is typically the largest. There is insufficient oxygen here for complete combustion, but now there are more carbon molecules that are present. When carbon molecules ignite, there is a full spectrum of light that is created. However, the yellowish portion of the spectrum is most dominant, so our eyes view this portion of the flame as yellow. Closer in the middle, this area is approximately 1000 degrees Celsius, but as it reaches the top temperatures rise to approximately 1200 degrees Celsius. Note that the brightest part of the flame is not the hottest!
The chemistry of a candle flame is actually a lot more complex and fascinating than I could possibly explain. Although a chemistry major in college, some of the breakdowns of a candle flame are enough to make my head spin.
So maybe it’s better if I just light my candle, sit back, and enjoy.
Happy candle burning ~