THE SCIENCE OF A CANDLE

One small flame,
a lot of science.

A candle does not burn wax. It burns wax vapour.

A single lit pillar candle on a ceramic tile on a wooden table in a dim room, its steady flame reflected softly on the tabletop — AI-generated image, not a photograph of a real person or place.

Melt, rise, vaporise
Blue where it burns
Yellow where soot glows
Faraday's candle, explained

Heat melts the wax, the wick lifts it, and the flame turns it into gas that meets the air. Michael Faraday built six famous lectures around that idea at the Royal Institution in 1860–61.

Updated 14 October 2026

THE SHORT ANSWER

Wax becomes gas,
gas becomes light.

A candle is a small fuel factory.
Each part of the flame has a job.

FUEL

It burns a gas

Heat from the flame melts a pool of wax. Capillary action draws it up the wick, where it turns to vapour and burns.

Try Faraday's tests

COLOUR

Blue base, yellow top

The blue regions are where the burning happens. The yellow comes from tiny soot particles glowing as they are heated.

Explore the zones

SAFETY

Treat it as a fire

Manchester's fire service says candles are one of the top five causes of fire in the home. Never leave one burning unattended.

Safe candle habits

INSIDE THE FLAME

Which part
are you looking at?

Pick a part of a candle flame to see what is happening there. The bar shows roughly how hot that part runs, from cooler to hottest.

Temperatures are approximate figures from a UK physics teaching site; zones are from a university combustion lecture.

Flame explorer

Choose a part of the flameThe dark centreThe yellow glowThe blue base and sidesThe outer edgeThe smoke after blowing out

The dark centre≈ 800 °C

A dark cone of wax vapour starts just below the curl of the wick. This vapour has not yet reached the air it needs to burn, and the centre runs cooler, at about 800 °C.

The yellow glowGlowing soot

Most of the candle's light comes from here. Carbon particles from the broken-down wax form soot, and the solid particles glow as they are heated.

The blue base and sidesReaction zone

Blue regions near the wick and along the sides mark where most of the burning happens. This reaction zone is where the highest temperatures are reached.

The outer edge≈ 1,400 °C

Faraday showed the heat sits in a ring, where the chemical action is, not in the middle. The outer part of the flame reaches about 1,400 °C.

The smoke after blowing outWax vapour

The trail is still wax vapour. Faraday showed a lit taper held two or three inches away sends a train of fire back down to the wick.

Sources: Matalon, Diffusion Flames lecture (CEFRC summer school, 2013); schoolphysics, Temperature of fire; Faraday, The Chemical History of a Candle.

TWO NUMBERS WORTH KNOWING

Hot at the edge,
cooler inside.

The flame is hollow in the middle.
The heat lives in a thin outer shell.

≈ 1,400°C

Outer part of a candle flame

A UK physics teaching site gives the outer part of a candle flame as about 1,400 °C, where wax vapour meets the oxygen in the air.

OUTER EDGE · SCHOOLPHYSICS

≈ 800°C

Centre of the same flame

The centre runs at about 800 °C. A paper test described by the Royal Society of Chemistry leaves a scorched ring, showing the flame is hollow.

CENTRE · SCHOOLPHYSICS

In microgravity, NASA explains, there is no buoyant convection to draw the flame up or carry soot to the tip, so a candle flame becomes spherical, soot-free and blue.

A thin trail of white smoke rising from a candle that has just been blown out, with a lit wooden taper held a few centimetres above it — AI-generated image, not a photograph of a real person or place.

FOUR THINGS FARADAY SHOWED

See the science,
safely.

Faraday's lectures, described by the Royal Society of Chemistry, used simple observations anyone can make. Watch with an adult present, on a heat-resistant surface, and keep hair and sleeves clear.

Look at the cup of wax
Below the flame, a small pool of melted wax forms. Faraday explained the fuel rises from it up the wick by capillary attraction.
Spot the colours
Look for blue near the base and sides, a dark centre and the bright yellow zone that gives most of the light.
Notice the shape
On Earth, rising hot air pulls the flame into a teardrop. NASA's images of flames in orbit show round, blue flames instead.
Watch the smoke
After blowing a candle out, the smoke trail is wax vapour. In Faraday's demonstration a lit taper relights the wick through it.

CANDLES AT HOME

Enjoy the flame,
respect the fire.

Greater Manchester Fire and Rescue Service advises putting candles in sturdy holders on a flat, heat-resistant surface, leaving at least 10 cm between two lit candles, and never placing them under shelves or near curtains.

Never leave a burning candle unattended, do not move one while it is lit, and put candles out before leaving the room or going to sleep. Battery LED candles give a similar look without a flame, and working smoke alarms on every level are essential.

A close-up of a candle flame against a dark background, with a small blue region at the base near the wick and a bright yellow tip — AI-generated image, not a photograph of a real person or place.

Questions

Questions people ask

What actually burns in a candle?

Wax vapour. Heat from the flame melts the wax, capillary action draws it up the wick, and it evaporates there. The Royal Society of Chemistry puts it simply: what is burned is a gas.

Why is a candle flame yellow?

Carbon from the broken-down wax forms tiny soot particles, and these glow as they are heated. Faraday said the flame owes its brilliancy to these solid particles.

Which part of the flame is hottest?

The outer part, where the wax vapour meets oxygen. A UK physics teaching site gives about 1,400 °C there and about 800 °C in the centre. Faraday found the heat lies in a ring.

Why does a candle flame point upwards?

On Earth, hot gases rise and draw in fresh air, giving a teardrop shape. NASA explains that in microgravity there is no such flow, so the flame becomes round and blue.

How far apart should candles be?

Greater Manchester Fire and Rescue Service advises at least 10 cm (four inches) between two lit candles, on a heat-resistant surface, away from curtains and never under shelves.

One small flame,
a lot of science.