Remember the concept of the melt pool? It's the softer wax which melts more quickly than the rest of the candle. You'll notice this wax will melt much more quickly on the second burn than it did the first time.
A good rule of thumb is that a candle will burn one hour per inch of the diameter of the candle. So, using my 12 oz Interlude jars again as an example, the top and the bottom diameters are 3 1/8", so you'll need to allow just over three hours for every burn.
But wait! These candles are hourglass shaped! You'll need to take into consideration the shape of the candle as well. At the "waist" of the candle, the diameter is probably closer to 2 3/4" inches. So while not a significant difference, you'll need to burn the candle just shy of three hours as the wax reaches the center, then you can burn it longer as the wax gets closer to the bottom of the jar.
Additionally, burn the candle only until you get 1/2" of a wax pool. Any more, and you risk the wax becoming too hot. The fragrance oil used is your candle is a combustible element.
Also, if the wax becomes too hot, the glass itself could break. Glass is a funny material; you may not be aware of tiny fissures existing in the container which could melt, causing a sudden breakage.
|Wax Warmer by DawnDavareDesigns|
So, what do you do if you didn't burn your candle correctly the first time, and each subsequent burn produces a lopsided candle? It's ok to scoop warm wax out of your container and create a level surface. Remember to use a spoon rather than a knife. Then treat the next burn as your would a first burn.
What to do with the left over wax? Put it in a wax warmer and enjoy the fragrance while it lasts!