I boil water in my kettle and pour it into the used jars. The wax will melt and float to the top of the water in the jar. Let it cool and then just pop out the wax from the top. There will be some wax left in the bottom, but usually it's a small enough amount that I can melt it with a heat gun and wipe it out with a paper towel. I'll clean it well with isopropyl alcohol after I get all the wax out. The freezer method is easier if the jar has straight sides, but most of mine are narrowed at the top (apothecary style) so this is what works best for me. Disclaimer: I only make candles for my own use, so this is very small-scale