Flame color can in part be decided by metal emission spectrums, that I know. But supposedly, the color could also be affected by the heat of the combustion, black body radiation. I’m wondering how these two come in to play and which ones matter. When burning normal candles the flame is usually yellow; when burning denatured alcohol the flame is blue (just had a fondue, that’s how I came up with the question); normal fires are usually a little orange. My question is: is this purely down to black body radiation, metals or a mix of both?

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    $\begingroup$ Re, "...candles...yellow." Candle flames are more complex than you might think. In the blue region at the base, you have the fuel decomposing to yield carbon and hydrogen. They hydrogen reacts promptly with oxygen, emitting the blue light. Meanwhile, the carbon condenses into soot particles, which subsequently burn in the yellow part of the flame. The yellow light is black-body radiation emitted by the hot, solid soot particles. $\endgroup$ Commented Feb 27, 2020 at 20:25
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    $\begingroup$ Re, "normal fires..." I'm guessing that when you say "normal," you might mean "cellulose" (e.g., wood, paper, cotton,...) and maybe other organic matter that's predominantly carbon, hydrogen, and oxygen. Organic stuff burns in a similar way to the candle flame except that the fuel initially decomposes into hydrogen, carbon, and water. The water, of course, does not contribute anything. $\endgroup$ Commented Feb 27, 2020 at 20:30
  • $\begingroup$ @SolomonSlow Yeah that’s right, thanks :) $\endgroup$
    – Melvin
    Commented Feb 27, 2020 at 20:37

1 Answer 1


It depends upon many conditions like amount of oxygen available in atmosphere. In practical colour is also determined by black body effect for example when a perfectly black body is heated up at high temperature it turns blue in colour and at low temperature it shows shades of red. For bodies that are not black body like various metals it is associated with excitation of electrons, on being heated up the electrons in metals attain an excited state and while coming to ground state the release energy in form of light of various wavelengths like in chemistry we study flame color imparted by various metals so it different depending upon the object


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