How to improve the burn of your handmade candles

A perfect burn depends on the balance between four variables: type of wax, wick diameter, pour temperature and curing time. Changing the wick has the biggest immediate impact, but diagnosing the problem correctly avoids unnecessary adjustments that make other aspects of the candle worse.

Your candle comes out of the mould looking good. You light it and the flame is too big, or a tunnel forms towards the centre, or the wick fills with black soot after fifteen minutes. You know something isn't working, but you're not sure which variable to change first. The temptation is to try smaller or larger wicks until something works, but that approach can create new problems while you solve the original one.

Diagnosis Before Adjustments

Every burn problem has a main cause and several secondary ones. Identifying the main cause saves time and material — and stops a correct adjustment to one variable from making another one's behaviour worse.

Tunnelling (the wax doesn't melt to the edges): The wick is too small for the diameter of the container, or the wax has a higher melting point than that wick can handle. It can also be insufficient curing time — a freshly made candle behaves differently from one cured for two weeks.

Flame too big or flickering: The wick is too large for the type of wax or for the diameter of the container. A big flame consumes wax faster than the wick can absorb it, creating an irregular pool of liquid wax that feeds the combustion poorly.

Black soot on the wick (mushrooming): The wick can't fully burn the carbon it produces. This happens when the wick is too large, when the wax has additives that don't burn cleanly, or when the candle hasn't cured enough.

Irregular wax pool: A pour temperature or wick centring problem. If the wax was poured too hot, it may have created internal tensions that affect how it melts during the burn.

Most makers adjust the wick without considering the other variables. It's the easiest change, but it isn't always the right one.

The Wick as Main Lever

The wick determines how much wax melts, at what speed, and how the heat is distributed. It's the variable with the biggest immediate impact on burn behaviour, but it isn't independent of the rest.

Wick diameter vs. container diameter: A wick should create a pool of liquid wax that reaches to within 1-2 cm of the edge of the container. If the pool stays in the centre, the wick is too small. If the liquid wax reaches the edge but the flame is very big, the wick is right for the diameter but may be too large for the type of wax.

Type of wick: Cotton wicks with a paper core work well with soy wax. Flat cotton wicks are better for harder waxes like paraffin. Wooden wicks create a wider flame and a larger pool, but require waxes with good hot throw because the combustion is less intense. Hot throw: the intensity of the scent the candle releases while burning.

Wick length: A wick that's too long produces a big flame and soot regardless of the diameter. Trimming to 5-6 mm before each use is critical — a 1 cm wick can ruin a candle that would work perfectly with the correct length.

What most makers discover in their second production run is that the same wick diameter can behave differently depending on the wax. A #2 wick that works well with soy wax can be too small for a soy-paraffin blend, even if the container is the same.

The Role of the Type of Wax

Not all waxes behave the same during the burn. The type of wax determines the melting point, the viscosity when liquid, and how it transmits heat to the edges of the container.

Pure soy wax: Low melting point, wide liquid-wax pool. Works well with medium-diameter wicks. The most common problem is frosting after putting the candle out, but that doesn't affect the burn — it's just appearance. Frosting: a white crystallisation on the surface of soy wax; a natural characteristic of the material, not a defect.

Soy-paraffin blends: Higher melting points, require slightly larger wicks or a longer curing time. The benefit is better hot throw and less frosting. The risk is tunnelling if you use the wick that worked with pure soy.

Paraffin: High melting point, smaller wax pool. Flat cotton wicks work better than core wicks. Cured paraffin burns more predictably than soy — fewer variables, more consistency between batches.

Beeswax: The densest and with the highest melting point. Requires larger wicks than the container diameter suggests. A wick that works for soy in an 8 cm container can be too small for beeswax in the same container.

The most common mistake here is assuming that one wick formula works for any wax. Every change of wax requires a burn test, even if the supplier is the same and only the blend ratio changes.

Pour Temperature and Its Effect on the Burn

The pour temperature affects how the wax structures itself when it solidifies. Wax poured too hot can create internal tensions that show up during the burn as irregular pools or flames that go out by themselves.

Soy wax: Pour between 50-60°C. Hotter and it can create air bubbles that affect the burn. Colder and it may not adhere well to the container, creating separations that let the liquid wax escape during the burn.

Soy-paraffin blends: Generally require a higher pour temperature, 60-70°C, for the components to integrate correctly. A badly integrated blend burns unpredictably.

Paraffin: Can be poured up to 80°C without problems, but a high temperature doesn't always improve the result. Pouring at 65-70°C gives better adhesion to the container without creating tensions.

A candle poured at the wrong temperature can have a perfect wick for its diameter and type of wax, yet still burn badly. It's the hardest variable to diagnose because the problem isn't visible until you light the candle.

Curing Time: The Most Underrated Variable

A freshly made candle is not the same candle as it is two weeks later. During curing, the wax stabilises, the fragrance oils integrate completely, and the molecular structure of the wax changes slightly.

Technical minimum: 24-48 hours for the wax to solidify completely and the wick to settle into its final position. A candle tested before this time can show burn problems that disappear on their own.

Performance optimum: 10-14 days for soy wax, 7-10 days for paraffin. During this period, the hot throw improves and the burn becomes more predictable. A candle that tunnels on the first day can burn perfectly in the second week.

Fragrance and curing: Fragrance oils affect the viscosity of the liquid wax during the burn. A candle with 8% fragrance behaves differently from the same wax without fragrance. Curing lets the oils distribute evenly instead of creating concentrations that alter the combustion.

Many makers test their candles too soon and make unnecessary adjustments. A wick that seems too small in a two-day-old candle can be perfect once the candle has fully cured.

Systematic Diagnostic Framework

Faced with a burn problem, this order of checks avoids changes that create new problems:

First: Curing time. Have at least 10 days passed since the pour? If not, wait before making adjustments. An uncured candle doesn't represent the final behaviour.

Second: Wick length. Trim to 5-6 mm and test again. A wick that's too long can mimic a wick that's too large.

Third: Wick diameter vs. container diameter. Measure the liquid-wax pool after 2 hours of burning. It should reach to within 1-2 cm of the edge. If it doesn't, go larger. If it reaches but the flame is excessive, the problem may lie in the type of wax or the original pour temperature.

Fourth: Consistency between batches. If one candle works well and the next, made with the same materials, doesn't, check the pour temperature and the mixing time. Inconsistency between batches is almost never a wick problem.

Fifth: Change log. Note each variable modified and the result. Burn problems have several possible causes, and it's easy to forget which combination worked when you test several wicks in a week.

Variables You Can't Fully Control

Some factors affect the burn but are outside the maker's direct control. Recognising them avoids unnecessary frustration.

Wax batch quality: Even the same supplier can have variations between batches. A wax that worked with a #2 wick may require a #3 in the next order, especially with natural waxes like soy.

Ambient humidity: Affects how the wick behaves during combustion. On very humid days, cotton wicks can absorb moisture and burn differently.

The exact container: Two containers of the same diameter can have different thermal conductivity depending on the material and thickness of the glass. A container that conducts more heat lets the wax melt further from the centre, mimicking a larger wick.

Draughts: A candle that burns perfectly in a sheltered spot can flicker or create soot in an area with moving air.

The question isn't how to eliminate these variables — it's how to design a candle that works well within a reasonable range of conditions. A slightly oversized wick can compensate for humidity variations. A longer curing time reduces sensitivity to differences between wax batches.

Specific Diagnostic Cases

A candle that starts well but develops problems after several hours: Generally a wick-too-large problem that shows up when the accumulated liquid wax exceeds the wick's absorption capacity. Try a smaller-diameter wick in the next batch.

A candle that works in small containers but not large ones: Wick scaling isn't linear. A 10 cm container doesn't need a wick twice as large as a 5 cm container. Consult equivalence tables specific to each type of wax.

A candle that burns well in winter but badly in summer: Room temperature affects the viscosity of the liquid wax. In summer, a wick that was correct can create pools that are too large. Consider slightly smaller wicks for spring-summer production.

A candle with fragrance that burns differently from one without: Fragrance oils alter the wax's behaviour. A high fragrance load (>8%) can require a smaller wick. Fragrances with high vanillin content can create more soot on the wick.

FAQ

How long should I let a candle burn to assess whether the wick is correct? At least 2 hours of continuous burning so the real pattern is established. In the first half hour, the wick is still adjusting and the wax isn't yet in its stable behaviour. Assess the diameter of the liquid-wax pool and the size of the flame after 2 hours.

Can I fix a tunnelling candle by changing only the wick of the finished candle? It's not advisable. Changing the wick of an already solidified candle can create air pockets or destabilise the structure. It's better to use that candle to learn (burning it for long periods so it eventually levels out) and apply the wick adjustment to the next batch.

Why does my candle work well for the first few uses but then develop black soot on the wick? Black soot appears when the wick can't fully burn the carbon it produces. This can get worse with use if the wax accumulated around the base of the wick changes the oxygenation. Trimming the wick to 5-6 mm before each use can solve the problem without changing the diameter.

Does the colour of the wax affect how the wick should be? Dyes in normal concentrations (up to 0.1% of the wax weight) don't significantly affect the burn. However, some liquid dyes contain oils that can alter the viscosity of the liquid wax during combustion. If you add dye and the burn changes, consider reducing the wick diameter slightly.

Should I use the same wick diameter for candles of the same size but different fragrances? It depends on the type of fragrance. Fragrances with a dense oil base can require a slightly smaller wick. Fragrances with a lot of alcohol can evaporate during the burn and allow a larger wick. If you produce candles commercially with multiple fragrances, run a burn test for each or use a conservative diameter that works for all.

What's the real difference between a cotton wick with a paper core and a flat one? Paper-core wicks keep their vertical shape and work better with soft waxes like soy. Flat wicks curl slightly during the burn, which can improve oxygenation in harder waxes like paraffin. For soy wax, the core wick is more predictable.

For candles that burn correctly from the first lighting, all the materials are available at Candeliss. Systematic diagnosis avoids wasting material on unnecessary adjustments. → See wicks and waxes at candeliss.com →