Candle Tunnelling: Why It Happens and How to Fix It

You light a new candle, enjoy it for an hour, blow it out, and a few burns later there is a narrow well down the middle and a thick wall of unused wax around the sides. That is tunnelling, and it is the most common reason candles burn out early and smell weaker than they should. The good news: it is almost entirely preventable, and usually fixable.

Why candles tunnel: wax memory

Wax has what candle makers call a memory. On each burn, the candle melts outward until you blow it out. Next time, it tends to melt only as far as that previous edge, the "memory ring". If the first burn is short and only a small pool forms around the wick, every later burn follows that small circle, and the candle drills down the middle.

Other causes include:

• A wick that is too small for the diameter of the container.
• Burning in a cold room or a draught, which cools the edges.
• Wicks trimmed too short or drowned in wax.

How to prevent tunnelling

1. Make the first burn long enough. Let the candle burn until the melted wax reaches the edge of the container all the way around. A common guide is about one hour for every 2.5 cm (one inch) of diameter. For our 200 g Fine Aromatic Candle, that usually takes two to three hours.
2. Repeat a full melt pool every time. Each burn should continue until the surface is fully liquid, but no longer than about three to four hours.
3. Trim the wick before each burn. For wooden wicks, about 3 to 4 mm; for cotton wicks, about 5 mm. See our guide to wooden wick candles.
4. Burn away from draughts, fans and air-conditioning vents, which create an uneven melt.
5. Keep the surface clean. Remove wick trimmings and debris, which can disturb the flame.

How to fix a tunnelled candle

The foil method

1. Light the candle.
2. Wrap a strip of aluminium foil around the top of the jar so it folds over the rim and covers the outer edge of the wax, leaving an opening of a few centimetres over the wick.
3. Let it burn for one to two hours. The foil reflects heat back onto the wax walls and melts them down level.
4. Remove the foil carefully with an oven glove once the surface is level and fully melted. It will be hot.

The oven or hair-dryer method

For a shallow tunnel, gently warming the top surface with a hair dryer, or placing a heatproof glass container in a low oven (around 80°C) for a few minutes, can level the wax. Only use this with heatproof containers, never with plastic, wood or decorated lids, and never leave it unattended.

If the wick is drowned

If the wick is buried in a deep tunnel, carefully pour off a little melted wax onto a paper towel (not down the sink) to expose more wick, then relight and use the foil method.

Burning tips that make candles last longer

• Never burn for more than about four hours at a time. Longer burns overheat the container and can make the flame too large and smoky.
• Stop when about 1 cm of wax is left in the bottom. Below that, the container can overheat.
• Use a snuffer or put the lid on to put the flame out, rather than blowing, which scatters smoke and wax.
• Let the wax set completely before relighting.

A well-burned candle not only lasts longer but also smells stronger, because a full melt pool releases more fragrance. For what goes into a good candle, read soy versus coconut versus paraffin wax.