How to choose a candle wick and fix tunnelling, sooting and frosting

TUREFF• •0

The wick is the engine of a candle. Choose the right one and the candle burns evenly, smells good and stays safe. Choose the wrong one and you get tunnelling, soot, huge flames or a flame that drowns. Most burning problems come back to wick size.

How wick size is chosen

The right wick depends on:

The diameter of the container or pillar: the most important factor. Wider candles need larger wicks, or more than one.
The wax type: soy, paraffin, beeswax and blends all burn differently. Beeswax usually needs a larger wick.
Fragrance and dye: both affect how the wax feeds the flame.
The wick series: different wick types (flat, square, cored, wooden and others) burn differently. Check the wick supplier's chart for your wax and diameter.

Wick charts are starting points. Test burn is the only reliable way to choose: make a few candles with different wick sizes and compare them.

What a good burn looks like

a steady, upright flame of moderate height, without flickering or smoking
a melt pool that reaches, or very nearly reaches, the edge of the container within a few hours
no soot on the container
a container that gets warm but not dangerously hot

During a test burn, check the flame height, melt pool and container temperature regularly, and burn the candle to the end in stages to see how it behaves as it gets lower. A wick that works at the top can misbehave near the bottom.

Tunnelling

Tunnelling is when the candle burns down the middle and leaves a thick wall of unmelted wax around the edges. Causes:

The first burn was too short. Wax tends to remember its first melt pool. A common guideline is to let the first burn run for roughly one hour per inch of diameter, or until the melt pool reaches the edges, without exceeding the burn time your supplier or label recommends.
The wick is too small for the diameter.
The candle is regularly burnt for short periods.

Fixes for makers: test a larger wick or a different wick series, or use two wicks in wide containers. For a tunnelled candle at home, some people wrap foil around the top so that it covers the unmelted rim with an opening over the flame, so heat reflects onto the edges. If you try this, stay with the candle, keep the foil away from the flame and stop if the container gets very hot.

Sooting and mushrooming

Soot shows as black smoke or black marks on the container. Mushrooming is a carbon blob on the end of the wick. Common causes:

The wick is too large for the candle.
The wick is too long: trim it to about a quarter of an inch (6 mm) before each burn.
Too much fragrance or dye.
Draughts making the flame flicker.

Fixes: trim the wick, move the candle out of draughts, try a smaller wick, and check you have not overloaded fragrance. A large, smoking flame is a safety warning as well as a cosmetic problem; put the candle out, let it cool and trim the wick before relighting.

Drowning

The opposite problem: the flame shrinks and goes out in its own melt pool. Usually the wick is too small, the fragrance load is too high or the wick has been trimmed too short.

Frosting

Frosting is a white, crystalline bloom on the surface or sides of natural waxes, especially soy. It is caused by the natural crystal growth of the wax and is cosmetic only: it does not affect how the candle burns or smells. To reduce it:

pour at the temperature your wax supplier recommends
warm containers slightly before pouring
let candles cool slowly, away from draughts and cold surfaces
try a wax blend designed to reduce frosting

Many makers accept some frosting as part of the look of natural wax.

Wet spots

Patches where the wax seems to pull away from the glass are called wet spots. They are usually cosmetic and come from the wax shrinking as it cools. Warming the jars before pouring and cooling slowly help.

Keep a test log

Record the container, wax, fragrance load, wick and burn results for every test. Patterns appear quickly. Which wick finally worked for your container? Share your results or ask about a problem candle in the comments.