You also want to make sure your container is not porous (able to absorb liquid). Ceramics are great to use for candle containers, but they need to be properly treated so that they are no longer porous. Porous, unglazed materials, such as clay flower pots, can actually act as a wick, making your flame grow to the rim of your container, and you could wind up with a much bigger flame than intended. So stick to something that doesn’t soak in liquids such as ceramic bowls and mugs.
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