Make a Green Fire Jack o’ Lantern

This is the original green fire jack o' lantern. Boric acid burns with an acid-green flame. (Anne Helmenstine)
This is the original green fire jack o’ lantern. Boric acid burns with an acid-green flame. (Anne Helmenstine)

Illuminating your Halloween jack o’ lantern with green fire is way more interesting than using a candle. Green fire just looks witchy! The effect is easy to achieve and yields fantastic results.

Green Fire Jack o’ Lantern Materials

You only need a few basic materials to put green fire in a pumpkin:

  • Carved jack o’ lantern
  • Boric acid or borax
  • Methanol
  • Long-handled lighter

Traditionally, the carved jack o’ lantern would be a pumpkin, but you can use any suitable produce. For example, consider using a watermelon, zucchini, or pineapple.

It really doesn’t matter whether you use boric acid or borax. Boric acid is sold in pharmacies as a disinfectant. Borax is sold as a laundry booster or a roach killer. The boron ion produces a green flame.

Methanol is sold as Heet fuel treatment. If you work in a lab, you may have it around as a solvent. If you don’t have methanol, substitute another form of alcohol, such as rubbing alcohol (isopropyl) or ethanol.

I recommend a long-handled lighter because alcohol has a high vapor pressure and tends to ignite suddenly.

Make the Green Fire

All you need to do is sprinkle the interior of the carved pumpkin with boric acid or borax, add a splash of alcohol, and light the fire. Nothing could be easier.

Tips and Tricks

Copper sulfate burns with more of a blue-green flame. (Anne Helmenstine)
Copper sulfate burns with more of a blue-green flame. (Anne Helmenstine)

Since I devised this project (has it been a decade already?), I’ve perfected the technique. So, here’s some advice:

  • To get the best display, line the bottom and back wall of the pumpkin interior with aluminum foil. It will reflect back the light, helping to illuminate the carved face.
  • Another option (to avoid that pumpkin pie cooked with lighter fluid scent) is to place the salt and fuel in a small metal or ceramic container inside the pumpkin.
  • Fire needs oxygen. So, you’ll get the best results using large, open carved eyes, nose, mouth, etc. The jack o’ lantern will work fine with its lid on, but will burn better if it’s left off.
  • If you can’t find borax or boric acid, the other chemical used to produce green fire is copper sulfate. This is sold as root killer or algicide. Copper sulfate does not dissolve in methanol to release the copper ion to make the green flame. If you use copper sulfate, the best fuel is rubbing alcohol or ethanol (about 70%). These fuels contain enough water to dissolve the salt, but enough alcohol to burn effectively.

See a Green Fire Jack o’ Lantern in Action

Although I’ve immolated pumpkins using all colors of fire, including rainbow fire and black flames, I go back to the green fire jack o’ lantern again and again. Here’s the original video of the project, so you can see what to expect.

Safety Information

  • Methanol is toxic. If you use it, avoid touching it and definitely don’t drink it.
  • This is a fire project, so there is a risk of burns and spreading the fire. The project should only be performed under responsible adult supervision.
  • Never add liquid fuel to a burning fire. Do not add fuel to the pumpkin unless the flame has been completely extinguished. Alcohol burns with a blue flame, which may be hard to see.
  • It’s best to perform this project outdoors on a heat-safe surface.
  • When working with fire, it’s always a good idea to have a fire extinguisher or bucket of water nearby. You can readily extinguish green fire by water or by suffocating it.