I’ve read two different reasons why this happens. One, there may be moisture around the candle when it’s lit and two, it’s a build up of carbon, and the candle has built up too much wax. I’m not sure what that means though - how can a candle build up more wax than what it started with? I ask because lately, my candles are “popping,” spewing soot around the sides of the candleholder. This happens after the first use, when the wick takes a different shape after being lit a few times. I put the lid of these candles back on after use so not sure how moisture could be getting in?