A Dance of Three Parts

It’s actually amazing to sit back and think about how candles work.  It’s one thing that makes this a very unique trade. The Romans were making and burning candles a long time ago, but we didn’t really have a popularized scientific explanation of what was going on until over two thousand years later!  (Thanks @michaelfaraday).

Any good fire has oxygen, heat, and fuel.  Take away any of these components and the fire will die.  It’s a careful balancing act of three parts that results in brilliant light and plentiful (hopefully GOOD) smells.  Candles are a lot like campfires… if a campfire had a giant wick in the middle. Let’s talk about that.

The flame, wick, and wax each play an important role in the structure of a candle.  Have you ever just tried burning a wick without wax or anything? It works just fine.  In fact it goes really fast! That’s because the cotton wick (remember that almost all modern wicks are cotton except wood wicks) is the only fuel for the flame and cotton burns really well.

The Wax is Fuel

So why even put the wick in the wax?  The difference is that we can take advantage of using the wax as EXTRA CANDLE FUEL.  Instead of using the wick as fuel, the candle repurposes it as a fancy transportation machine.  Through the incredible power of science, liquid wax naturally rises up through the wick and directly into the fire where it heats up until it straight up vaporizes.

If we could somehow take a burning candle and pluck off the flame, underneath would be a wick saturated with liquid wax.  Putting the flame back allows the liquid inside the wick to heat up until it turns into vapor. Since the vapor is flammable it immediately reacts with the heat source (we’ll talk about that “reaction” in a second).  The liquid-turned-vapor is immediately replenished inside the wick which makes for an extremely efficient refueling system.

Scented Candles

Okay.  So how do those scrumptious scents seamlessly serve smells?

It’s all in the “reaction” mentioned earlier.  The vapor (which is pretty much gas) immediately ignites because it’s flammable (and there’s tons of oxygen around) and turns into light, heat and other products (carbon dioxide and water, when things go well).  Scientists call this combustion and humanity has used this phenomenon to power cars and put people on the moon.  We use it to craft humble little lights.

Scented candles take advantage of this whole process by putting fragrance oils directly into the wax.  As part of the liquid wax FUEL moving into the wick and transformed into vapor, the combustion of vapor that has the presence of fragrance oil particles gives off an aroma (in addition to the normal by-products of the candle).

Safety First

Combustion is the goal, but the reality is that an imbalance of fuel, oxygen and heat will create more than just the normal critters (CO2, H2O, and aromas).  This incomplete-ness of the burn causes more byproducts. Not all of them have warm fuzzy names, but they’re not so concentrated or large to cause concern (no matter the wax type).

But it’s important that fuel created by the wax is burned off in time to control the heat build-up and amount of vapor.  If the candle doesn’t burn fast enough AND still manages to generate a large amount of heat, the vapor can build up and create a significant fire risk… that vapor is flammable!  We rely on that vapor being flammable, remember. But we also assume as users of the candles that the producer designed a combustion system appropriate for the wax fuel and that the candle is safe to burn.

It’s not always a safe assumption, unfortunately.  Poorly designed (or poorly kept, sometimes) candles are known to cause house fires.  It’s so important that candles, especially retail candles, meet a safety standard.  It’s actually relatively hard to design a candle that operates as a fire hazard, but it’s not impossible. 

The stories I’ve read and heard about candles exploding have a common theme of candles being set near a hot surface while operating… the heat melts more wax than can be burned up naturally through the wick and increases the potential for more vapor to be created.  More vapor = more flammable gas = greater risk. These types of situations are why there is a safety sticker on the bottom of every candle with burning recommendations and guidelines. Who reads the bottom of their candles? No idea. Boring people, maybe. But I guess it removes the excuse!