Also called: tunneling, candle tunnel
Why do candles tunnel?
In short
Tunnelling is when only the wax around the wick melts and burns down, leaving a hard wall of unburnt wax against the container. It is usually blamed on how the candle was burned, but the dominant cause is an undersized wick, one that can never make enough heat to reach the rim.
The usual explanation, and why it's incomplete
The standard advice is that tunnelling is caused by not burning the candle long enough the first time. There is something to this, a candle does need long enough on each burn to melt all the way out, but it has become an explanation that puts the blame on the person holding the match, and it obscures the more common cause.
If a wick is too small for the diameter of its container, it cannot generate enough heat to reach the wall no matter how long you burn it. You can leave that candle lit all evening and the outer ring will still be solid. That is not a burning mistake. That is a candle that was built wrong.
How to tell which one you've got
- Burn it for three to four hours in one go, with no draught. A correctly wicked container candle should reach the wall in that time.
- If it reaches the edge, the wick is fine and the earlier tunnelling was down to short burns. Keep giving it full burns and it will recover.
- If it still doesn't, the wick is undersized. No burning technique will fix it, and the candle will keep tunnelling for the rest of its life.
What makers get wrong
Wick selection is not a single lookup. It depends on the inside diameter of the vessel, the particular wax, and the fragrance load, fragrance changes how the wax burns. Supplier charts are a starting point, not an answer, and the only way to confirm a wick is to test-burn the finished candle. It is also worth knowing that wick numbers do not translate between series: a size 10 in one family is unrelated to a size 10 in another.
A note on "memory rings". You will often read that wax "remembers" its first burn. The observable behaviour is real, a candle that was first burned short does tend to keep tunnelling, but wax has no memory. What is actually happening is simpler: a solidified ledge of wax at the rim sits further from the flame and is harder to reach, so each subsequent burn struggles in the same place. The practical advice is the same; the mechanism isn't magic.
Rescuing a tunnelled candle
If the wick is adequate, several long uninterrupted burns will gradually even it out. Where the wall is already established, the commonly suggested trick is wrapping foil around the rim to reflect heat inward, which can work but needs supervising and will not fix an undersized wick. Keeping the wick trimmed helps the flame burn cleanly and at full size.
Good to know
Questions people actually ask
Is tunnelling my fault?
Often not. Short first burns contribute, but an undersized wick causes tunnelling regardless of how carefully the candle is burned. Test it with one long burn, if it still will not reach the wall, the candle was under-wicked.
How long should the first burn be?
Long enough to melt right out to the container wall, which for most jars means a few hours. The commonly cited rule of roughly an hour per inch of diameter is a reasonable starting point.
Can a tunnelled candle be saved?
Sometimes. Several long, uninterrupted burns can gradually reclaim the wall if the wick is big enough. If it is not, the candle will not recover.
Make one that burns properly
A Candle Craft session pairs your vessel and scent with a wick that suits them, so the candle you take home burns to the edge.