A glass container candle that burns all available fuel at it's end of life is a potential hazard. As a measure of safety, some wax should remain at the bottom of a candle to prevent a flashover or a fire hazard condition at end of life. We use an industry standard 20x6mm wick sustainer, which will result in approx 1/3" of unused wax at the bottom of the candle vessel. This wax can be safely removed and discarded or composted, and the vessel can be cleaned and reused. We size our candles based on their estimated burn times and not the amount of wax in the vessel.