Those are really cute!! I used to make ceramics. Basically all ceramics is, is glazed clay. As long as there are no cracks in the glaze, they should burn ok, for at least the first burn. The high heat of the candle might cause it to crack, then it is very porous. Perhaps there was an unseen crack towards the bottom, or it might not have been properly glazed & fired that caused the candle to burst into flames. Most imported ceramics are very, very thin & won't take too much heat over & over. PamR ps. if you use ceramic dishes to eat on, the same is true. If you start to see cracks in the glaze, or chips, it is best to discard. Alot of the imported ceramics still contain lead.