Candles are a girls best friendKatie Self discusses the discovery of diamond particles in a candle flame.

We’ve all had that lovely, romantic, candlelit dinner, but what is it that makes a candle so seductive?

Scientists and philosophers have been intrigued by candles since the first one was invented in China more than 2000 years ago.

In a lecture given to the prestigious Royal Society in 1860 entitled ‘The Chemical History of a Candle’, Michael Faraday (a scientist famed for being the father of electricity) said of candlelight “You have the glittering beauty of gold and silver, and the still higher lustre of jewels, like the ruby and diamond; but none of these rival the brilliancy and beauty of flame. What diamond can shine like flame?”

Well, as it turns out, the shine of diamond and flame are one and the same. In 2011, Professor Wuzong Zhou and his student Mr. Zixue Su from our own Department of Chemistry here at the University of St Andrews made a fascinating new discovery: approximately 1.5 million nanoparticles of diamond are generated in a candle flame for every second that it burns.

This discovery came about after a fellow scientist challenged Prof. Zhou. In a university press release 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,”

This is the first time scientists have been able to see what actually happens in a candle flame. The wax that burns when a candle is alight is made of long chained hydrocarbons which were already known to combust and form carbon dioxide and water by the time they reach the top of the candle flame but until now the process from hydrocarbon to carbon dioxide was unknown.

By formulating a new sampling technique which involved designing a series of ultra-thin porous anodic aluminium oxide (AAO) foils, Prof. Zhou and Mr. Su were able to extract soot particles from the very centre of a candle flame. Upon analysing these particles Zhou found, to his surprise, that they consisted of all four known forms of carbon: graphitic carbon, fullerenes, amorphous carbon and, of course, diamond!

This is particularly fascinating as the four different carbon forms are generally produced under extremely different conditions. Diamonds, of course, require extremely high pressures to be manufactured and are formed naturally only after thousands or even millions of years at these pressures. Fullerenes, or ‘Bucky Balls’, on the other hand, are frequently manufactured by a low pressure method where an electric discharge is passed between two carbon electrodes in a helium atmosphere. The soot is then collected and dissolved in a solvent such as benzene before the fullerenes are extracted.

Despite this, it seems both forms of carbon (along with amorphous and graphitic carbon) are being synthesized simultaneously every time you have that lovely, romantic, candlelit dinner. This leap in science could lead to new research into how diamonds, which are a key substance in industry, could be manufactured using a cheaper and more environmentally friendly method.

Prof. Zhou also added: “Unfortunately the diamond particles are burned away in the process, and converted into carbon dioxide, but this will change the way we view a candle flame forever.”

“My research shows that it is possible to see diamonds in flame, but this also gives us a chance to think about whether diamonds can be formed in a different way.”

Sadly, a great deal more research will need to be conducted into this topic before anyone will be extracting the diamonds out of candle flames on a larger scale than for anything but simple scientific curiosity. But perhaps, while that’s going on, some of the slicker boyfriends out there may be able to convince their partners that a candle is just as good a gift, if not better, than a diamond. What could be nicer than making 1.5 million diamonds of your own, every second, whenever and wherever you want them! … Well, it may take some convincing, but it’s worth a try.


Katie Self


Image by L.C.Nøttaasen