Have you ever wondered how the fragrance of your burning candle makes its way to your nose? Or, more importantly, why is that when you burn your new scented candle, you don’t smell it after an hour of burning? This blog explains how the fragrance or essential oils from a scented candle make it to your nose, and then highlights the key factors that improve the diffusion (or hot throw) of those oils.
How a fragrance gets to your nose
First, in simple terms, how does a fragrance get from the candle to your nose. There are two ways this happens; one is known as “cold throw” and the other is known as “hot throw”. Cold throw is the fragrance you smell when the candle is unlit and cold. Usually you need to smell the candle up close for cold throw, like you do at the store before you buy your favorite candle. As you may have guessed, hot throw is the fragrance you smell when you get it home and burn it. In both cases, you’re smelling the molecules of oils released from the candle. The difference is that the molecules from a cold candle have a much harder time moving through the candle and escaping into the air where they eventually meet with the olfactory receptors in your nose. Not surprisingly, it would take an extremely long time for cold throw to fill a room with fragrance.
Key factors that improve the diffusion of oils for stronger fragrance
So now let’s focus on what happens when you burn the candle. The journey of those oil molecules traveling to your nose is called diffusion , which is governed by laws of diffusion. In other words, there are scientific equations that can determine the amount of diffusion you can expect from different candles. But you don’t need to understand any of these equations because I simplify them down to some key factors that improve the diffusion of those oils in your scented candle. Here they are in order of most to least impactful:
Distance from your nose to the candle – the further the candle is, the longer it takes the oil molecules to reach your nose. This is why you can smell the cold throw from a candle in the store because you generally put your nose right up to it. You can control this factor.
Temperature of the wax – the higher the temperature of the wax, the more energy you give the oil molecules to collide with each other and evaporate into the air, where they diffuse through the air in your kitchen and eventually to your nose. You may not think you can control this factor, but you can, as I explain in the next section.
Viscosity of the candle wax – this is a measure of how hard it is to move something through the wax (a warm wax has more friction than a hot wax). The more viscous, the more difficult it is for fragrance molecules to diffuse through the wax. You can control this through the wax temperature.
Concentration of the oils in a candle – adding a higher concentration of oils to a candle is like increasing the dimmer switch on your light, the higher the oil concentration (higher voltage) the higher the rate of diffusion (brighter light). Higher cost candles tend to use more oil.
Molecular weight (i.e. size) of the oil molecule – smaller, lighter molecules travel faster than larger, heavier ones. This is why you may smell some notes early in burning your candle, compared to 2 hours later. I’ve yet to see candle vendors publish the molecular weight of their oils, so it’s not realistic for us to choose a candle based on this.
Airflow in the room – if the air is completely still in the room, it will take longer for the molecules to diffuse from the candle to the far edge of the room. Using a ceiling fan is a good way to help diffuse the fragrance in the room. The small fan in the VelaRosa candle diffuser also helps diffusing the fragrance.
Size of the melted candle wax pool – more surface area from which to evaporate some molecules. The size of the melted pool is related to the temperature of the wax so you can control this.
Increasing the temperature of your scented candle wax
When you first light your candle, the wax is at room temperature and for jar candles, it will take over an hour to get the wax temperature hot enough to melt into a full pool and become less viscous. But there are some things you can do to speed up this process to increase the fragrance diffusion in your room.
Burn multi-wick candles – the more wicks you have the quicker you melt the wax, the hotter the wax pool gets, the more oil molecules are evaporated into the air. Note that the thicker the candle wick is, the more wax and oils travel up the wick and get vaporized by the candle flame. However, choosing a candle based on wick thickness isn’t very practical.
Use a candle topper – candle toppers are more than decorative, they retain the heat from the candle flame which decreases the time it takes to develop a full wax pool.
Use a candle fragrance diffuser – the VelaRosa candle fragrance diffuser uses the heat from a tea light candle to melt the top wax layer into a pool in less than 10 minutes at over 50°C (122°F). And in about 30 minutes, 100% of the wax in a tea light candle melts at a temperature of over 80°C (176°F). That means the oil molecules have more energy to evaporate from the wax into the air. This temperature also reduces the wax viscosity, making it easier for the oil molecules to move around. For those of you who burn soy candles, the VelaRosa diffuser is ideal for soy tea light candles because the molecular structure of soy wax is more dense (higher viscosity) than paraffin wax, which takes a higher temperature to increase the diffusion of the oils.
I attached the graph below that shows the wax temperatures over time for all three candles. It shows that the VelaRosa diffuser is able to melt the wax about 8 times faster than the 3-wick candle and even faster compared to the 1-wick candle. The 3-wick candle reached a maximum temperature of 90.7°C (195°F) after 3 hours 20 minutes of burning but the VelaRosa diffuser reached this temperature after only 31 minutes. All of this simply means that the VelaRosa diffuser can fill your room with oil fragrance much faster than a 3-wick candle, using only a tea light.
When it comes to decorating our homes with fragrance, there are plenty of products available, but none offer the warmth and primal feeling we get when we burn a scented candle. So the next time you’re sitting by candle light and can’t smell your candle, think about how you can make the fragrance stronger, so you can enjoy the fragrance you paid for.
VelaRosa diffuser is estimated to be available in May 2021. Sign up for our email list to stay notified:
Click here for email list sign-up
 Measured as the amount of oil molecules per cm2 per second (unit area per unit time)