The wax is the fuel, not the wick
It looks as if a candle burns its WICK, but the wick is mostly a pipe. The heat of the FLAME MELTS a little pool of WAX at the top of the candle. The liquid wax is drawn up the woven wick by capillary action, the same effect that pulls water up a paper towel. Near the flame it turns into a gas, and it is that wax vapour that actually BURNS. The yellow glow comes from tiny specks of soot heated until they shine.
In 1848 the scientist Michael Faraday gave a famous series of Christmas lectures for young people at the Royal Institution in London called The Chemical History of a Candle, using nothing but candles to explain combustion, air and chemistry. You can see his point with a simple trick: blow a candle out and hold a lit match in the thin trail of smoke just above it, and the flame jumps down the vapour and relights the wick. Our states of matter page covers solids, liquids and gases.
From smelly fat to soy
For most of history ordinary candles were made from tallow, animal fat, which was cheap but smoky and smelt of what it was. Beeswax burned cleanly and smelt sweet, but it was expensive, so it was used mainly by churches and the wealthy. In the nineteenth century paraffin wax, made from crude oil, became cheap and clean-burning and replaced both.
SOY wax, made from soya beans, and other plant waxes have become popular with home candle makers since the 1990s. They melt at a lower temperature, clean up easily with soapy water, and hold a SCENT well.
Melting wax safely
Wax should never be heated directly in a pan on the hob. It is melted in a heatproof jug standing in a pan of simmering water, known as a double boiler, which keeps the temperature well below the point where wax can catch fire. A wax fire must never be put out with water; covering it with a lid smothers it. Home candle making is a job for adults, or children with an adult right there.
Once melted, a DYE adds COLOUR and a candle-safe FRAGRANCE oil adds scent. The wax is poured into a MOULD or a CONTAINER such as a glass JAR, with the wick held straight in the middle by a clip or a pencil laid across the top.
Curing, trimming and the first burn
Wax needs time to HARDEN fully, and scented candles are often left to CURE for several days so the fragrance spreads through the wax. Before each lighting, it helps to TRIM the wick to about half a centimetre, which gives a steady, less smoky flame.
The first burn matters most: let it go long enough for the melted pool to reach the edges. Put it out too soon and the candle can tunnel, burning a narrow hole down the middle and wasting the wax around it. Candles come in many forms — a chunky PILLAR, a slim TAPER for a candlestick, a small VOTIVE in a holder — and all of them turn a simple CRAFT into warm LIGHT.