While a flame is the gaseous portion of a fire, a candle flame contains millions of diamond nanoparticles. Approximately 1.5 million diamond nanoparticles are created every second before converting into carbon dioxide. All four forms of carbon are present within a candle flame: elemental carbon, graphite, white carbon and diamond.
A flame can become hot enough that the atoms of its gaseous portion lose their electrons and become ionized, producing plasma. The type of fuel used in combustion determines the color and temperature of the flame. In zero-gravity or low-gravity conditions, a flame appears spherical and is more likely to be blue due to the absence of natural convection.