Candle soot can be a real headache. You're burning a candle only to find that there's a black smoky substance coming from your flame. Well, the good news is that there are a number of ways that you can reduce the amount of soot that comes from your candles. Not only will they burn better, but you'll have a much better candle experience and save money.
So, first things first, where does soot come from? Every candle is fueled by its wax, and the wick is the vehicle, which creates a capillary action, that carries the fuel to keep the flame burning. A process, called combustion, is what happens when you have a carbon (in this case, wax) react with oxygen in the air. The reaction creates light and the burning fuel produces carbon dioxide. Steam, in small amounts, is also a produced as the flame melts the wax, as well as smoke. The smoke is basically from the minuscule particles of carbon in the wax (that weren't completely burned) combined with a bit of steam. This produces a black smoky substance from the flame (carbon) that causes your walls, fixtures and such to become black when the carbon is released into the air.
When you light a candle, the blue part of the flame that you see is where the steam is produced. In this area, the wax is clean burning with lots of oxygen (hence, the blue color). A bit further up, in the bright yellow part of the flame, is where the smoke is created. This is because the oxygen is pulled up the wick at the bottom and heat is given off at the top of the flame, giving off hot air. There is not enough oxygen that reaches the top of the flame to create a perfect combustion process.
What Are You Talking About?
All that being said, your candle needs a consistent amount of fuel, a steady flame and oxygen to burn well. The key word is consistent. So, if I were to place my candle by the window, where there's a gentle breeze, just because I want to give it oxygen, it would create an inconsistent flame, causing the flame to become larger and then smaller. It would create a large "flicker" from your flame. This happens because the flame is bouncing around in the draft and causes the wick to require larger amounts of fuel. When the flame becomes smaller, in the flickering process, it's not going to burn all the fuel that it took in when the flame was larger and the extra fuel is burned off as carbon or soot.
One way that many people see as a help for this problem is to contain free standing candles, such as votive and pillars, in cylindrical container to keep the draft from the candle flame. While it may seem to make sense, since cylinder containers have a closed bottom, it's going to limit the oxygen that the candle will need for its flame to consistently burn. In fact, it's almost like being in any closed in space where oxygen is limited. The oxygen will be used more quickly and will run out in such a small, enclosed space. Remember, your flame will need oxygen to burn and that oxygen will largely come from the lower area surrounding the flame. If the lower air is trapped and the flame can only pull from the oxygen coming in from the top of the container, there's a fight as the steam that's produced by the burning candle is trying to escape. This conflict will produce soot and cause the inner part of the cylinder container to become black. One way to combat this issue is to use a cylinder with an open bottom to create air flow from the bottom of the container. Then, raise the cylinder just a bit at its bottom to allow air to enter in from the bottom. This can be done by taking something about the height of a tea light container and placing one on four areas of the bottom of the bottomless cylinder. This would raise the container enough to allow air to come in through the bottom. Remember to always use something stable to raise your candle vase.
Keep Things Trim
One of the absolute best, and easiest, ways to keep soot down when you're burning a candle is to keep the wick trimmed to about ¼". When you first light a candle, you want to make sure that the candle is trimmed down to that ¼" length so that you don't start off with a high flame. If you find that the flame is dancing and your candle isn't in a drafty room, you'll likely need to trim the wick a bit more. This is one of those reasons why a candle should never be left to itself. If your flame gets too high, it could really mean trouble. However, keeping your candle wick trimmed will keep your flame under control and allow a better burn with less soot.
Go With Cotton
Try to get candles made with cotton wicks, rather than lead wicks (that are more prone to producing carbon). Cotton fibers absorb wax best because of its fibers that pull in the wax. It aids in producing a cleaner burn. Ask your candle maker which types of wicks are used in their candle making process.
As a side note, when purchasing candles, it's good to have some knowledge about who you're buying from. Always keep in mind what type of candle you're looking for, whether it's one that's designed more for aesthetics or one designed for a great scent or just illumination. Buy from someone you trust is going to give you a quality product for what you're looking for and one who is knowledgeable about candle making.
Also find out why candles burn a hole straight through the middle here.