A candle is burning

Candles give off a feeling of peace, warmth and comfort. We often use them during Advent and Christmas, for birthdays or at a festive meal. Before electric power was available, candles were used to light rooms. The only other options were torches or oil and tallow lamps. Handling candles has always been hazardous, as their flames can easily set other things alight. But what exactly is a candle? And what happens when it burns? Inside a candle is a cotton thread called a wick, surrounded by wax. In the past, candles were made from real beeswax. In the Middle Ages, beeswax was therefore an important trade good, especially because so many candles were burned in churches. Today, candle wax is usually made from stearin, which is derived from fat and oil.

Wax melts at a temperature of just 60° Celsius. A match or a lighter is usually used to light a candle. First, use it to set fire to the tip of the wick protruding from the wax. The burning wick heats the candle wax. A small amount of wax melts. The liquid wax rises up the wick and turns into the gases carbon and hydrogen. Oxygen then enters from the surrounding air. The hydrogen turns into water vapour. The tiny carbon particles combine with the oxygen and become so hot that they glow. This creates a flame that we can see and that lights up the surroundings.

So the parts that actually burn are components of the wax. As long as the flame is burning, wax rises, is transformed, and its combustible components keep the flame going.

The flame has different zones with different temperatures:

In Zone 1, the wax first melts. But it does not burn yet. It is about 600° Celsius, rises up the wick and evaporates at its tip.

In Zone 2, oxygen enters from the outside. The wax burns, producing carbon and hydrogen. The temperature here is about 800 °C.

In Zone 3, the hydrogen vaporizes, while the carbon burns. This produces the flame’s bright glow. If the carbon particles do not burn completely, soot forms. Temperatures of about 1400° Celsius occur at the flame’s surface. Toward the tip, the flame gets darker as the temperature drops again.

Candles come in different colours because wax can be dyed easily. The flame, however, shines white on all candles.

There is always a small gap between the flame and the wick. That’s a good thing, because otherwise the wick would burn up much too quickly. And what happens when we blow out the candle? We blow air towards the flame. The air pushes the wax away from the wick, and the wick cools down. Then no more wax can rise up. The flame goes out.