A candle is many things. In some small ways, a candle is like a pet. Just like a pet there are little things you can learn about your candle that will help you take care of it in the best ways possible.
Burn Time and Tunneling
When a candle is burning, it is a delicate balance of solid, liquid, and gas. The flame melts the solid wax and oil mixture, then turns it into a liquid. As the liquid melts it releases the oil into the air. As the oil and wax get closer to the wick, it releases into flame, and the flame repeats the cycle.
A small minority of our candles will not properly burn and the flame doesn't get hot enough to melt the wax around the edge. This forms a tunnel and an effect we call "tunneling"
:( A very sad state indeed!
Sometimes the cause of this is because of too much oil in the candle for it to burn (especially in some of our earlier recipes of coffeehouse), but in most cases, this has to do with how long you burn the candle. If you burn your candle an amount of time that is too short (less than 45 minutes) it will begin to create layers of unmelted wax that will start to effect the constitution of our candles and cause tunneling. If you burn your candle too long it will superheat the sites of the glass and cause them to become black.
To prevent tunnelling always let your candle melt the wax all the way around the jar.
To fix a candle that has already tunnelled, you can scoop out the layers of wax around the wick to give your wick a chance. Alternatively you can use tinfoil to hold in the heat and melt the surrounding wax.