Science in GIFs: Lighting a candle by its vapor trail
Candles are a very clever invention. Wax is the fuel but it will only burn as a vapour - liquid and solid wax will not burn. Lighting a candle melts the solid wax in and near the wick. Liquid wax is then drawn up into the wick by capillary action. The heat of the flame vaporises the liquid wax and the vapour burns providing enough heat to keep the process going at just the right rate.
The wick is usually made from an absorbent twine. As the wax vaporises, it cools the wick and prevents it from being completely burnt. Evaporation is a cooling process, which many animals exploit by sweating. When sweat evaporates, the body is cooled slightly (in high humidity, sweat does not evaporate as readily and accumulates on the skin).
The smoke from an extinguished candle contains unburnt wax vapour (candle fuel) and is therefore flammable. If this vapour trail is ignited, the flame can travel back to the wick and start the process of melting, vaporising and ignition all over again. Via
