The first time you light a candle you are setting a boundary it will follow for the rest of its life. Get it wrong and you will throw away a third of what you paid for.
Here is what is actually happening.
Wax memory
Container candles behave as though they remember. On the first burn the wax melts outward from the wick to a certain diameter, and then you blow it out. Every subsequent burn tends to melt to roughly that same diameter and no further.
So if your first burn only reached a small circle, the candle has effectively set its own edge, and the wax outside it will stay solid however long you burn it afterwards. That is tunnelling, and it is caused entirely by use rather than by manufacture.
How long, exactly
The rule
Burn until the melted pool reaches the edges of the container all the way round. For most candles that is roughly one hour per inch of diameter.
Judge by the edge rather than by the clock. The pool reaching the glass is the finish line, and the timing is only a guide.
In practice, that means a small candle wants an hour or so and a wider one wants longer. Our small glass jar candles at £12.99 are the most forgiving, and the tall jars at £24.99 need the longest first burn because they are the widest.
The practical consequence is that a candle is a poor choice for a ten minute moment on its first outing. Light it when you have an evening.
Why an untrimmed wick makes it worse
A long wick produces a larger, hotter, more turbulent flame that consumes wax quickly and unevenly, and produces soot that blackens the glass.
Trim to around 5mm before every burn, including the first. Trim it cold rather than hot, and remove the trimmings from the wax before lighting. If the wick has a mushroom of carbon on the end, that is a wick asking to be trimmed.
The four hour limit
The other end of the same problem. Burning too long overheats the container, makes the wax too fluid and lets the wick drift or mushroom.
Four hours is the usual maximum. Put it out, let it cool completely, trim the wick, and light it again if you want more.
Rescuing one that has already tunnelled
Genuinely effective, and worth knowing before throwing a candle away.
Wrap kitchen foil around the top of the container, folding it inward over the rim so it forms a dome with a hole in the middle above the wick. Light it and let it burn with the foil in place.
The foil reflects heat down onto the unburnt wax at the edges, melting it back into the pool. After an hour or two the surface should have levelled. Remove the foil carefully, since it will be hot, and let it cool flat.
You may need to repeat once. It does not work on a candle that has tunnelled so deeply that the wick sits below the surrounding wax, because the flame cannot reach the edges at all.
Draughts, and the British windowsill problem
A draught pushes the flame sideways, which melts the wax unevenly and makes the candle burn down at an angle. It also makes the flame smoke.
British windowsills are the classic offender, because even a closed window in an older house moves enough air to affect a flame. Next to a door, under a wall vent, or above a radiator are the other three.
If a candle is burning down one side, move it before assuming the wick was badly set.
When to stop for good
Stop when around a centimetre of wax remains. Below that the container gets hot enough to be a genuine hazard, particularly with glass.
The remaining wax is not wasted. Warm the jar gently in a bowl of hot water, lift the wax out and use it in an oil burner as a melt, which recovers the last of the fragrance safely.
Our guide to why candles tunnel covers the whole subject, and choosing a scented candle that suits the room covers matching scent to space. The full range is in decorative scented candles.
Questions people ask
How long should a candle burn the first time?
Until the melted pool reaches the edges of the container all the way round, which is roughly one hour per inch of diameter. Judge by the edge rather than the clock.
Why does the first burn matter so much?
Wax has a memory. Subsequent burns melt to roughly the same diameter as the first, so a short first burn permanently sets a narrow boundary.
How do I fix a tunnelled candle?
Wrap foil around the top, folded inward to form a dome with a hole above the wick, and burn for an hour or two. Reflected heat melts the edge wax back into the pool.
How long is too long?
Four hours. Beyond that the container overheats, the wax becomes too fluid and the wick can drift or mushroom.
Should I trim the wick before the first burn?
Yes, to around 5mm, and before every burn afterwards. A long wick burns hotter and more unevenly and produces soot.
