How to Make Blue Fire


Make Blue Fire
Make blue fire either using a fuel that burns blue or else by adding a metal salt that emits blue light to a flame.

You can make blue fire for a chemistry demonstration, Halloween decoration, or “magic” trick. While many fuels burn blue, you need a flame colorant to get a vivid blue flame. Here’s what to do and how to avoid common pitfalls.

Blue Fire
Copper chloride in methanol burns with a turquoise blue flame.

How to Make Blue Fire

Blue fire works like the flame test in chemistry. You dissolve a metal salt in a solvent and mix it with a fuel. Some fuels naturally burn blue. Some compounds not only contain ions that emit blue light, but also include a color enhancer (usually chlorine).

Blue Fire Method #1

  • Copper(I) chloride
  • Hydrochloric acid (HCl)
  • Alcohol (or other blue-burning fuel)
  • Glass container
  • Glass rod or wooden spoon (if using a wooden spoon, don’t use it for food afterward)
  1. Dissolve copper(I) chloride in the minimum-necessary amount of hydrochloric acid. Don’t use a metal container or utensils because HCl reacts with metal. Glass is best.
  2. Mix in alcohol.
  3. Ignite the fuel for the turquoise blue fire.

You can find copper chloride online as a pure chemical from Amazon or firework/pyrotechnic stores. Check the label so you know if you have copper(I) chloride or copper(II) chloride.

Hydrochloric acid is sold as muriatic acid at home supply stores. Wear gloves and goggles when working with it and do not touch the mixture (because it’s acidic). This blue fire method is suitable as a chemistry demonstration.

Blue Fire Method #2 (Safest Method)

  • Copper(II) chloride (CuCl2)
  • Alcohol
  1. Dissolve copper(II) chloride in alcohol.
  2. Ignite the fuel and enjoy the blue fire.

Most copper(II) compounds burn green, but copper(II) halides (like copper(II) chloride) burn blue. Copper(II) chloride is easier and safer to work with because it’s soluble in water, methanol, ethanol, and acetone (no acid needed). It’s available online from Amazon, pyrotechnic stores, and chemical supply companies. It’s more soluble in methanol than ethanol or rubbing alcohol, but methanol is toxic to touch or inhale.

For the safest blue fire, just dissolve the copper(II) chloride in rubbing alcohol or ethanol. You can wash metal, plastic, or glass containers or utensils and use them afterward like normal. But, if you use a wooden spoon, it absorbs some copper chloride and cannot be used in the kitchen.

Blue Fire Method #3

  • Copper(II) sulfate
  • Hydrochloric acid
  • Methanol
  1. Dissolve copper sulfate using hydrochloric acid.
  2. Mix the solution into the methanol.
  3. Ignite the fuel for the blue fire.

Copper(II) sulfate or copper sulfate pentahydrate is readily available as an algicide and root killer. Unlike copper chloride, it’s often available in home supply stores as well as online. If you dissolve copper sulfate in methanol and burn the fuel, you get a bright green flame. However, dissolving the salt in hydrochloric acid supplies free chlorine that turns the flame turquoise blue.

Now, if you want to customize the blue fire or can’t find the recommended chemicals, consider using another fuel that burns blue or another metal salt. (There is also the old method burning a bit of copper pipe stuffed into an old green plastic garden hose, but that is not advised because burning plastic produces nasty and almost certainly toxic smoke.)

Fuels That Burn Blue

As a general rule, clean fuels burn colorless to blue, while “dirty” burn yellow. Basically, non-fuel compounds often include sodium, which has an overwhelming yellow emission that drowns out other colors.

Fuels that burn blue are:

  • Ethanol (ethyl alcohol)
  • Isopropanol (isopropyl or rubbing alcohol)
  • Methanol (methyl alcohol)
  • Butane
  • Propane
  • Natural gas
  • Methane

Fuels that do not burn blue are wood, candle wax, hydrogen (red), gasoline, diesel, kerosene, and coal.

Flame Colorants to Make Blue Fire

There are different shades of blue. Use this table to customize a flame for the blue color you want. Keep in mind, some elements and their compounds are toxic. For example, lead and arsenic are readily available and make blue fire, but aren’t great options for most applications because of their toxicity. Most of the time you’ll find these elements as metal salts or other compounds. The other elements(s) in the compound affect the color, so some experimentation may be in order to get the desired effect. Some compounds dissolve in water, some in alcohol or acetone, and others require acid.

SymbolNameColor
AsArsenicBlue
BiBismuthAzure
CsCesiumBlue-violet
Cu(I)Copper(I)Turquoise blue
Cu(II)Copper(II) halide (non-halides are green)Turquoise blue
GeGermaniumPale blue
InIndium (named for its flame test color)Indigo blue
NbNiobiumGreen-blue
PPhosphorusPale blue-green
PbLeadBlue-white
SeSeleniumAzure
SnTinBlue-white
TaTantalumBlue
ZnZincColorless to blue-green

Aside from copper(I) chloride, probably the best blue fire colorant is Paris green, which is copper acetoarsenite. Paris green is insoluble in either water or alcohol. It is soluble but unstable in acid. I mention it because of its historical significance as a blue fire colorant and because you may accidentally see this color if you burn treated lumber (which you shouldn’t, because the fumes are toxic). Arsenic and its compounds are toxic, so avoid this colorant.

A Note About Copper

Most people making blue fire opt for copper chloride, which yields a turquoise blue flame, pretty much regardless of whether you use copper(I) chloride or copper(II) chloride. These compounds work because they dissociate into their ions and release Cu+ or Cu2+ and Cl. Free chlorine in the flame is necessary to get the blue color. Copper carbonate, hydroxide, oxide, and other copper compounds largely emit green and red light, with very little blue.

Firework compositions often include other compounds as chlorine donors, but these aren’t usually environmentally friendly and are not recommended (e.g., polyvinyl chloride or PVC; mercury chloride or calomel; chlorocarbons like DDT). If you need a chlorine donor, opt for something tamer, like ammonium chloride (NH4Cl) or hexachlorobenzene (C6Cl6).

Also, copper chloride only yields a blue flame at relatively cool flame temperatures. Using a fuel that burns too hot ruins the effect.

Safety Information

  • These instructions are for educational and decorative purposes. Because fire is hot and can burn things, this isn’t a project for young children.
  • Please exercise caution if you use hydrochloric acid and/or methanol. If you spill the acid, neutralize it with baking soda or another weak base and then clean the spill with water.
  • Methanol is a handy chemical, but it’s toxic. Only use it outdoors or under a fume hood. Follow any cautions listed on the product container.
  • Follow safety instructions on the flame colorant chemicals. Copper sulfate and copper chloride are safe to work with, but don’t eat or drink them.
  • There isn’t really any smoke from burning copper chloride or copper sulfate in a clean fuel. That being said, don’t cook your hotdogs or roast marshmallows over chemically colored flames (just to be safe).

References

  • Barrett, Seth M.; et al. (2020). “Exploring Emission and Absorption Spectroscopy in the First-Year General Chemistry Laboratory”. Journal of Chemical Education. 97(11): 4097-4102. doi:10.1021/acs.jchemed.0c00234
  • Bretz, Stacey Lowery; Murata Mayo, Ana Vasquez (2018). “Development of the Flame Test Concept Inventory: Measuring Student Thinking about Atomic Emission”. Journal of Chemical Education. 95(1): 17-27. doi:10.1021/acs.jchemed.7b00594
  • Landis, Arthur M.; Davies, Malonne I.; Landis, Linda; Thomas, Nicholas C. (2009). “‘Magic Eraser’ Flame Tests”. Journal of Chemical Education. 86 (5): 577. doi:10.1021/ed086p577
  • Sanger, Michael J.; Phelps, Amy J.; Banks, Catherine (2004). “Simple Flame Test Techniques Using Cotton Swabs”. Journal of Chemical Education81 (7): 969. doi:10.1021/ed081p969
  • Wilson, Charley (February 16, 2018). “Chlorine Donor Pyrotechnic Chemicals.” Skylighter.com.