Candle flames contain millions of tiny diamond particles, a university professor has discovered.

Research by Wuzong Zhou, a professor of chemistry at the University of St Andrews in Fife, revealed that around 1.5 million diamond nanoparticles are created in a candle flame every second it is burning.

Dr Zhou used a new sampling technique to remove particles from the centre of the flame, which is believed to have never been done before, and found that it contained all four known forms of carbon.

He said: "This was a surprise because each form is usually created under different conditions."

Dr Zhou added that the diamond particles are burned away in the process, but the discovery could lead to future research into how diamonds could be created more cheaply, and in a more environmentally friendly way.

He said: "This will change the way we view a candle flame forever."

The academic said he uncovered the secret after a challenge from a fellow scientist in combustion.

Dr Zhou said: "A colleague at another university said to me: 'Of course no one knows what a candle flame is actually made of.

"I told him I believed science could explain everything eventually, so I decided to find out."

The first candle is said to have been invented in China more than 2,000 years ago, and previous research has shown that hydro-carbon molecules at the bottom of the flame are converted into carbon dioxide by the top of the flame.

However, the process in between has remained a mystery until now, with the discovery of the diamond nanoparticles, as well as fullerenic particles and graphitic and amorphous carbon.

Rosey Barnet, artistic director of one of Scotland's biggest candle manufacturers, Shearer Candles, said the discovery was "exciting".

She said: "We were thrilled to hear about the discovery that diamond particles exist in a candle flame.

"Although currently there is no way of extracting these particles, it is still an exciting find and one that could change the way people view candles.

"The research at St Andrews University will be of interest to the entire candle making industry.