Black marks can be removed, once the candle has been extinguished, with a cloth soaked in warm water and soap. Take care not to get any moisture on the glass or wax before lighting your candle again.
Here are a few tips on how to use it that will save you this inconvenience:
- Cut the wick regularly to a length of 3-5mm. This will allow the candle to burn for longer and prevent the wick from emitting smoke or turning black and falling into the liquid wax.
- Make sure you recentre the wick in the wax after each use. This will allow the wax to burn more evenly. It will also prevent the wick from getting too close to the glass and potentially overheating it.