Our Concrete Vessels are 100% handmade, are sustainable, and reusable. These vessels are unique in their own way. They may have very small air bubbles or imperfections which is very natural with using concrete. That does not affect the vessels for candle use :) **If you choose the sealed vessels ** our vessels are sealed twice inside with a water based, non-toxic, no VOC sealer. Please keep in mind that if you plan on wetting or washing the vessel, allow 24 hours to fully dry before using for candles. These Vessels are also great to use as mini planters, for school projects, for painting, and/or Home Decor. Please allow an additional 2-4 days of shipping as these are made upon ordering. PLEASE TEST YOUR CANDLES! START WITH A SMALLER SIZE WICK FIRST TO ENSURE NO OVER-BURN OR CRACKING HAPPENS. MAX BURN TIME FOR THESE CONCRETE CANDLE VESSELS ARE 2-3 HOURS, NO MORE THAN THAT :)