Tunnelling happens when a candle burns straight down through the centre, leaving a ring of unmelted wax around the edges. Over time this narrow tunnel gets deeper, the flame gets smaller, and a large amount of wax is left unused when the wick eventually cannot reach it anymore.
Tunnelling almost always starts on the first burn. If a candle is extinguished before the entire top layer of wax has melted from edge to edge, the wax develops a kind of memory, and it will keep burning within that same narrow circle on every future burn.
A wick that is too small for the diameter of the candle will also struggle to create a full, even melt pool, since it simply cannot generate enough heat to reach the edges of a wide container. Burning a candle in a drafty spot can cause the flame to flicker unevenly, which also encourages one side to melt faster than the other.
If the tunnel is not too deep, you can sometimes correct it by burning the candle for a longer session, often four hours or more, to give the melt pool time to reach the edges. Wrapping foil loosely around the top of the container to trap heat inward can also help widen the melt pool on a stubborn candle. For a candle with a very deep tunnel, some people carefully trim down the surrounding wax with a knife so the wick is level with a smaller, more manageable pool.
The simplest fix is prevention: give every new candle a full first burn, generally one to two hours per inch of diameter, until the wax pool reaches all the way to the edge of the container. This single habit prevents the vast majority of tunnelling issues.
.svg)
.svg)
.svg)
.svg)
.svg)
.svg)
.svg)
.svg)
.svg)
