If you quickly burn through your favorite candles like I do, throwing away the glass jars might feel wasteful. I recommend you clean the jar and reuse it as home decor such as a flower vase, as a small storage container, as a pen holder for your office, or any other creative idea you may have!
When is it time to say goodbye to a candle? Generally, when 1/2-inch of wax remains at the bottom of the jar you should stop burning it. Burning a candle past this point can damage the container or even the surface it's sitting on.
To clean wide-mouth candle jars such as the ones we use, place your spent candle on a protective surface, like a dish towel or a potholder. Next, pour boiling water into the jar, leaving an inch of space at the top. The boiling water will melt the candle wax, causing it to float to the surface of the jar. Let cool completely before removing the wax. Strain the water and remaining candle bits, and avoid getting wax in the sink drain. Then clean the jar with soap and water.
Viola! - now you have a handy glass jar for use as you please!