Looking for an over-the-top science-y Halloween jack o’ lantern? Here’s my favorite… a carved pumpkin that’s both covered in colored flames and shoots fire from every orifice. The colors work much like the analytical chemistry flame test in which heated ions release a characteristic spectrum of light.
- Real Pumpkin (fake probably would melt, which might be something to try, I guess)
You have a few household chemical options for the colorant. My personal favorite is boric acid, which is sold as a roach killer powder or as a disinfectant powder. It emits a green light when heated. Borax, sold as a laundry booster, also burns green. Another choice is copper sulfate, which I have found in granular form as a root killer. Any or all of these work well.
The best fuel for the exterior of the pumpkin is hand sanitizer gel, which is 60-65% alcohol. You can use just hand sanitizer, but for big interior flames, it’s nice to have rubbing alcohol, kerosene, or methyl alcohol (Heet fuel treatment). My favorite combo is methanol (Heet) inside the pumpkin and hand sanitizer on the outside of the pumpkin.
Alcohol and hand sanitizer burn with a blue flame. Natural salts in the pumpkin produce yellow and orange, while incandescence covers the other colors of the spectrum.
Make a Rainbow of Colored Fire
- Prepare your pumpkin. Carve it. Don’t carve it. Whatever floats your boat.
- Either go outdoors or else place your jack o’ lantern on a heat-safe surface, such as a cookie sheet on top of a potholder. Unless you get crazy, it should be easy to extinguish the flames by blowing them out, but it’s never a bad idea to have a source of water or a fire extinguisher at hand,
- Smear hand sanitizer all over the outside of the pumpkin. One nice feature of the product is that you’re left with water when the alcohol burns off, which puts out the fire.
- Sprinkle your colorant inside and outside the pumpkin.
- Pour a small amount (couple of ounces) of fuel into the jack o’ lantern.
- Use a long-handled lighter to ignite the fuel.
- You can re-charge the fire after the flames go out. Don’t add fuel to a burning pumpkin! There is no need to add more colorant chemical, as it is not consumed.
The carving is up to you. It’s not even critical to clean out the seeds and other pumpkin guts, since you don’t need to reach your hand inside the jack o’ lantern to place a candle. Anyway, the interior get immolated if you do it right, so it’s sort of a self-cleaning pumpkin.
Ready to see it in action? Here’s my video…
It’s a FIRE project. It makes an excellent Halloween chemistry demonstration or holiday display, but should only be under the control of a responsible adult. Have fun, but please be careful. Also, don’t use the pumpkin for pie or otherwise ingest it following this project. The colorant chemicals are more harmful to invertebrates (copper) and plants (too much boron) than to people, but they aren’t food. The fuels range from bad-tasting (ethanol) to downright toxic (methanol or kerosene). Read the warning labels on the products you use.