All the vessels are stress and heat-tested, and we use the vessels as candles to test them ourselves before making them new again and putting them on the marketplace. Included are safety instructions for any upcycled vessel on the recommended maximum burn time and advice not to allow the wicks to burn right to the bottom in the case of some vessels, along with standard candle safety advisory. Vegetable/natural waxes burn at a much lower temperature than paraffin wax and so do not heat the containers as much, which is why in upcycled containers its best not to burn the candle right down to the end and always leave a small amount of wax.