• Question: Why is fire orange?

    Asked by crunchiejelly to Amy, Drew, Julia, Kimberley, Sara on 20 Jun 2011. This question was also asked by smartiepants.
    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 20 Jun 2011:

      Hi again crunchiejelly! I love how many great questions you ask! You seem like a very curious person. That’s a great quality to have =)

      Fires are actually different colors depending on the material being burned and the temperature. Really hot flames will be blue. Cooler flames will be orange or yellow. A flame cools and changes color as it moves away from the source of the flame, because it is exposed to more oxygen. Fire requires oxygen to burn, and since the bottom of a candle flame does not get much oxygen, it is the hottest spot in the flame and is blue in color. The temperature change causes the color of the flame to change from blue, at the hottest, lower portion of the flame, to the usual bright orange color we normally think of. Which shade of orange is seen at the upper portion of the flame, where the flame is the coolest, depends upon the material being burned. The strong orange color in wood fires is usually from sodium. This is because the atoms of sodium emit light strongest in the visible wavelengths of orange color.

    • Photo: Drew Rae

      Drew Rae answered on 20 Jun 2011:

      Hi again Crunchie Jelly. Sara has covered pretty much all of the question. Here’s a few fun facts to add:
      Copper burns green. Lithium burns bright crimson. Pure sodium burns very yellow. You can make coloured flame by mixing metal salts with the wax in candles, or putting filings of the substance into a gas flame. Don’t try it with things like phosphorous or potassium, but copper is fun and safe.

    • Photo: Amy MacQueen

      Amy MacQueen answered on 20 Jun 2011:

      Hi!!!

      So Sara got here first but here is my answer! Fire is orange partly because of extreme heating of unburned carbon particles and partly because of sodium (which burns with an orange flame) contained in the material being burned. It also depends on the temperature of the flame – very hot flames are bluish in colour (as when the air vent is open on a Bunsen burner and sufficient oxygen is available for complete combustion meaning there is no unburnt carbon) while cooler ones are orange (like when the air vent on the Bunsen burner is closed and incomplete combustion occurs)

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