What is tunnelling?
Tunnelling happens when the centre of the candle melts, leaving a thick wall of unmelted wax along the sides of the jar that persists as the candle burns down.
The first burn is important because it sets the candle’s “memory” for how evenly it will melt. If the wax does not melt across the surface, the resulting ring of solid wax around the container, known as a memory ring, encourages tunnelling on later burns.
Why does tunnelling happen?
Tunnelling is often caused by extinguishing the candle too early, before the melt pool has reached the edges of the jar.
The candle’s flame concentrates heat near the wick, melting the surrounding wax. If the first burn does not create a full melt pool, subsequent burns deepen the tunnel, with the flame sinking lower and its heat becoming less effective at melting the wax left behind.
Why is tunnelling a problem?
• Wasted wax: Unused wax at the sides of the jar shortens the candle’s total burn time.
• Weak scent throw: A restricted melt pool exposes less liquid wax to the air, weakening fragrance release.
How to prevent tunnelling
• First burn rule: Let the candle burn until the melt pool reaches the edges of the jar—usually 2–4 hours, depending on size and the candle maker’s instructions.
• Trim the wick: Cut it to ¼ inch before each burn to keep the flame stable and centred.
• Avoid short burns: Burn long enough each time to form a full melt pool.
While a short first burn is a common cause of tunnelling, other factors can contribute.
What other factors can cause tunnelling?
Wick size
Tunnelling can also happen when the wick is too small, known as under-wicking. An under-wicked candle cannot generate enough heat for a full melt pool.
Check for under-wicking: If a candle consistently fails to reach a full melt pool despite adequate burn time, the wick may be too small.
Wick length
Trimming the wick too short can also cause tunnelling because a short wick does not produce the heat needed for a full melt pool. Trim to ¼ inch, or follow the length advised on the label.
Unused wax does not have to go to waste; a simple foil method can help correct a tunnelled candle.
How to fix tunnelling with the foil method
- Light the candle as you normally would.
- Wrap a piece of aluminum foil around the upper part of the candle jar. Extend the foil1–2 inches above the rim.
- Fold the excess foil inward, leaving an opening so the flame gets enough air.
- Let the candle burn. The foil holds more heat around the top of the jar, helping the wax along the edges melt. Continue until the top surface is liquid. Keep the candle within sight while the foil is in place, and put out the flame if the jar becomes excessively hot.
- Extinguish the candle and let the foil cool before removing it.
Once the wax has cooled and hardened, the surface should be more even for the next burn.