There is a good candle burn and a bad candle burn! We test all of our candles to make sure they are on their best behavior! What you want to see is a clear burn, a clean sided glass, even pools of wax melted to the edges without black smoke on the rim. See above!
To achieve these types of burns, always light the candle the first time for long enough that the melted wax reaches the edges of the container. This will help prevent tunneling and wasting wax. Plan on burning your candle for at least 2 hrs at a time for the best results thereafter.
This type of burn will make it easier to clean the glasses for repurposing!