What Chemical Turns Fire Green?

Green Flame
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Green is possibly the coolest color to turn flames. It's not a color you get from the fuel, so you have to add a chemical to get the effect. The color comes from the ion emission spectra, so you can use any of the chemicals that produce green in the analytical method known as the flame test. The most readily available compounds are:

  • boric acid (boron compounds), sold as a disinfectant and roach killer
  • borax (boron compounds), sold as a laundry booster and home cleaner
  • copper sulfate (copper(II) compounds), sold as a root killer and algicide

However, other chemicals will make green flames:

  • thallium compounds
  • antimony compounds
  • barium compounds
  • manganese (II) compounds
  • molybdenum compounds
  • ammonium compounds
  • phosphates moistened with sulfuric acid

How to Get Green Fire

If you add any of these chemicals to a fire, you'll get green flames. The trouble is, there might be other chemicals in your fuel that can overpower the green, making it impossible to see. You can add copper compounds to wood fire and get a range of colors, including green. Most of the other colorants won't work with a campfire or fireplace fire because sodium in the fuel emits a bright yellow light that overpowers the green color.

The best way to get green fire is to heat the chemicals in a blue gas flame or to add them to an alcohol-based fuel. In addition to gel fuels, you can use methanol, ethanol, and isopropanol.

Safety Information

None of these chemicals is edible and a few are toxic, so don't roast marshmallows, hot dogs, or other food over a green fire. Having said that, the boron and copper compounds are relatively safe in that they aren't consumed by the fire, so they don't really add to the toxicity of any smoke, plus they are household chemicals that can be washed down the drain.

If you are using colorants on a camping trip or outdoors, be aware of the effects of the chemicals on the environment. High levels of boron compounds can be toxic to some plants. High levels of copper compounds can be harmful to invertebrates. These are properties that help make these chemicals useful in the home, but not so great for wild habitats.

Use care with methanol (wood alcohol) and isopropanol (rubbing alcohol), since these fuels are absorbed through the skin and are toxic. Any alcohol on skin increases its permeability, so it's best to avoid touching any solution of metal salts, even if the solvent is ethanol.