One method is pouring boiling water into the jars, which melts the wax. The wax is supposed to float to the top of the water and then cool in an easy-to-remove layer. I chose two candles for trying this method.
Sure enough, the wax started to liquefy just moments after the boiling water was poured. I let the water cool overnight and found a nice layer of wax on top the next morning. However, there was still wax left at the bottom of both jars. Maybe this method is best for jars with very little wax left. As a side note, I discovered that my green jar was actually coated with a green waxy film in order to color the glass. Even with all the wax removed from the candle, the inside walls would still feel waxy, so I'm not sure if this candle jar is still useful to me. Maybe I'll use it to hold a homemade candle?
Another method for removing wax is to put the candle in the freezer. Frozen wax can be chipped out a lot easier than room-temperature wax. I found this method to be very effective. There were a few remnants of wax left inside the jar, so I decided to try the boiling water method to get the last bits off.
Not only did most of the wax bits float off of the previously frozen jars, but it took care of the remaining wax from one of the boiling water jars. I was expecting another thin layer of wax, and at least two more rounds of boiling water before this jar was completely clean. In fact, the layer of wax was so thick on top that it was hard to remove.
Now I have some cool free glass jars! I love the fact that some candles come with air-tight lids, too. I can't wait to find something to store in these.
Oh, and I saved the wax. Are you surprised? I just may have to make that homemade candle after all...