1) What is a sinkhole in candles?

A sinkhole is an internal void, a cavity that forms in the wax as it cools, usually around the wick, in the area where the wax contracts the most. On the outside the candle can look perfect, but on the inside an empty space is left.

3) Is a sinkhole a defect of the wax?

Most of the time, no. It’s a normal phenomenon for many pillar waxes (paraffin, paraffin + stearin, some blends for moulds). The difference isn’t whether it appears, but how you deal with it (poking + a proper top-up).

4) Where does the sinkhole appear in candles poured in moulds?

In pillar candles poured in moulds, the sinkhole usually appears in the filling area (at the top, during pouring), that is, in the part that later becomes the bottom of the candle, not the visible top.

5) Which type of wax makes sinkholes most often?

Pillar paraffin: high risk (strong contraction). Paraffin + stearin: high risk, but controllable (a stable recipe for events). Soy for moulds: medium risk (craters and dips). Container soy: low risk (mostly surface dips). Beeswax: can form internal voids, but it sticks strongly to moulds; for shapes, silicone moulds are often used.

6) How can I tell if I have a sinkhole when the surface looks perfect?

Typical signs: the “crust” gives way when you press lightly next to the wick; sometimes you hear a small “pop”; when burning, the candle goes well for a few minutes, then the flame “drops” and is smothered.

7) Why can a sinkhole smother the wick?

When the flame reaches the cavity, you can get: a sudden collapse of the material; melted wax pooling in the void; the wick drowning or being smothered. The result: the candle goes out or burns unevenly.

8) When is the right moment to poke the holes?

When the wax is still slightly warm, not completely cold. At that point the material lets the air out and “takes” the top-up better. If you wait too long, you risk imperfect bonding or visible lines at the top-up.

9) Why does the “two holes rule” work better?

Because when you pour the top-up wax into one hole, the air in the cavity has to have a way out. The second hole works as an “exit” for the air. With a single hole, the wax can block the exit and air stays trapped underneath, so the sinkhole appears again.

10) What temperature should the top-up wax be?

As a practical rule, the top-up wax should be about 5–10 °C warmer than the initial pouring temperature. The idea is for it to melt the edges slightly and “weld” itself to the body of the candle, not sit there like a separate plug.

11) Why does a line or a visible area appear after the top-up?

Usually for 3 reasons: the top-up wax was too cold; the top-up was done too late (the candle was stone cold); too much was poured and it went above the initial level. The fix: the right temperature, the right moment, a moderate top-up.

12) Does the wick affect the sinkhole?

The wick doesn’t “create” the sinkhole, but it can make it worse if: it’s too slack (it bends as the wax contracts); it’s off-centre. That’s why the tension of the wick is essential: in the workshop, the wick has to be pulled taut and centred before pouring.

13) Can I prevent sinkholes completely?

Rarely 100%, especially with paraffin and pillar blends. What you can do is reduce it and keep it under control: the right temperatures; cooling without thermal shock; poking + top-up at the right moment; a centred, taut wick.

14) If I got it wrong and the sinkhole is big, can I still save the candle?

In most cases, yes, if you haven’t damaged the walls of the mould and if you do the top-up properly. If the hole is very large or several cavities have formed, it’s sometimes more efficient to make the piece again (especially for event candles, where stability is critical).

15) Does a sinkhole mean my materials are bad?

Not necessarily. Sometimes it’s the other way round: clean materials suited to pillar candles have natural contraction. What matters is having: a stable recipe (e.g. paraffin + stearin for events); a repeatable process (poking + top-up); the right wick.

Why a hole forms next to the wick: sinkholes

Q: 2) Why does a hole appear next to the wick after cooling?

Because wax contracts as it sets. The outside (the walls of the mould and the top of the pour) hardens first, while the inside stays liquid for longer. When the inside cools and its volume drops, it “pulls” the material down and leaves a void behind.

Why does a hole appear next to the wick after cooling? The sinkhole and our Servus workshop strategy

17 February 2026 | Materii Prime – Blog | SINZIANA SUTO

You poured the candle perfectly.

The mould was prepared, the wick centred, the wax poured at the right temperature. You leave it to cool and, when you take it out, it looks flawless: smooth, straight, glossy.

Then you press lightly with your finger next to the wick and… pop. The surface breaks and underneath you find an empty cavern, hidden treacherously under a perfect crust.

If this has happened to you, you didn’t do anything wrong. You’ve met one of the most common and most frustrating phenomena in candle pouring: the sinkhole.

I’m Sînziana, from the Servus workshop in Maramureș, Romania. This phenomenon is no stranger to us. We see it every season, in hundreds of candles poured in tall moulds, on our stainless steel table where every wick is centred with patience. The sinkhole isn’t a mysterious defect, nor a failure on the maker’s part. It’s the way the wax shows you it has worked naturally on the inside, even if on the surface it seemed calm.

1. The physics behind the "lying candle"

You didn’t get the wax wrong. You’ve met the physics of materials.

Wax, especially paraffin and blends with stearin, contracts strongly when it goes from liquid to solid. The process is simple, but inevitable:

The wax cools first where it touches the walls of the mould and at the surface.
A solid "shell" forms, which fixes the outer shape.
The centre stays liquid for longer, insulated by this shell.
When the centre starts to cool, its volume drops and it "pulls" the material down.

Because the surface is already hard, a void is left underneath: an air pocket which, if it isn’t dealt with, can smother the wick after the first few minutes of burning.

It isn’t magic. It isn’t a defect. It’s the natural behaviour of wax poured in moulds.

2. How the different types of wax behave (observations from the Servus workshop)

In the workshop we don’t talk from textbooks, but from what we see every day when we take the candles out of the moulds. After hundreds of pours, the pattern becomes clear:

Type of wax	Behaviour on cooling	Sinkhole risk	Servus recommendation
Paraffin (pillar)	Strong contraction, deep cavities	High	Almost always needs a top-up
Paraffin + stearin	Rigid structure, controlled contraction	High, controllable	Ideal for stable event candles
Soy for moulds	Moderate contraction, shallow craters	Medium	Needs careful poking and levelling
Beeswax	Moderate contraction, can form voids; strong adhesion to moulds	Medium	Prefers silicone moulds, not rigid metal
Container soy	Minimal contraction, sticks to the glass	Low	Easily corrected with warm air

These observations aren’t theory. They’re the result of real candles, taken out of the moulds in the morning and checked one by one.

3. The "gold standard" recipe for event candles

Pouring wax into mould tubes in the Servus workshop For candles that have to withstand ceremonies, handling and transport, in the workshop we use a classic blend: type 1 paraffin + vegetable stearin.

Why do we add stearin?

It increases the hardness and the stability of the candle in the heat
It gives that opaque, clean white typical of ceremony candles
It helps a more controlled release from metal moulds
It disciplines the flame and reduces drips down the sides

In short, paraffin provides the fuel and stearin provides the control. Together they make a denser, more stable candle that burns more predictably.

4. The Servus difference: the "two holes" rule

Online you’ll often read that you should "poke it with a knitting needle". In the workshop we’ve learned that improvisation doesn’t help when you work with tall wedding candles.

We use a thin metal rod with a wooden handle, made specially to reach the base of the candles. The procedure is simple and repeated every time:

We leave the candles to cool for between 4 and 12 hours, depending on diameter and height.
We step in while the wax is still slightly warm, not completely cold.
We bring the tool down vertically, close against the wick, almost to the base.

The real secret is that we always make two opposite holes, next to the wick. When you pour the hot top-up wax into one hole, the air in the cavern has to have a way out. If you make a single hole, the wax blocks the exit, the air stays trapped and the sinkhole comes back.

5. The right wicking: the detail that keeps the candle straight

A sinkhole can also be made worse by a wick that’s chosen or tensioned wrongly. In our production we’ve set a simple, but tested, correlation:

Diameter 3.5 cm → 3×8 wick
Diameter 4.5 cm → 3×8 wick
Diameter 5.5 cm → 3×10 wick
Diameter 7 cm → 3×12 wick

But it isn’t only the size that matters, it’s the tension too. When the wax contracts, it puts considerable force on the wick. If it isn’t centred and pulled taut properly, the mass of wax can bend it slightly towards one wall, and the candle will burn crooked and run down one side.

For a detailed explanation of choosing the right wick for each diameter and type of wax, see our dedicated technical guide: how to choose the right candle wick

6. How to fix a sinkhole properly (workshop checklist)

Mould tubes filled with green and pink wax, cooling in the Servus workshop The top-up isn’t done at random, nor in a hurry. Our steps are simple, but they take patience:

Make controlled holes using the two-holes method, next to the wick.
Heat the top-up wax to about 5–10 °C above the initial pouring temperature, so it bonds properly to the body of the candle.
Pour only enough to level the void, without going above the initial pouring line.
Let the candle settle slowly, with no cold draughts or forced cooling.

The exact temperatures differ depending on the type of wax and the diameter of the candle, and they’re best learned from repeated tests, not from a single rushed pour.

Conclusion: the calm behind a stable candle

The hole next to the wick isn’t an enemy. It’s only the sign that the material worked quietly, on the inside. In the workshop we’ve learned not to be alarmed by these signs, but to understand them and to step in calmly, at the right moment.

The difference between an amateur and a professional isn’t the absence of problems, but the way they read them. A stable candle isn’t built from a single perfect pour, but from patience, observation and small gestures repeated correctly.

If you want to work with waxes suited to candles poured in moulds and to keep this phenomenon better under control, you can explore the materials made for pillar candles: wax for moulds and pillar candles

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