Black marks are a result of the wick being too long or too close to the glass.
These can easily be removed using a damp cloth, ensuring the candle has been snuffed out first. 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 avoid your candle producing back smoke:
- Trim the wick regularly to a length of 3 to 5 mm. 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.