Fire Texting: How to Write Secret Messages with Fire

How to Write Secret Messages with Fire

Writing secret notes with lemon juice was one of my favorite pastimes as a child. All it took was a small flame to lightly scorch the paper and reveal the hidden message. Now that I'm tall and pay bills, lemon ink just isn't exciting enough anymore. Luckily, we can use another kind of invisible ink to write in fire! By using the saltpeter, we can whip up invisible fire ink in no time.


  • Saltpeter (aka potassium nitrate)
  • Water
  • Thick paper
  • Cotton swab or paintbrush
  • Match or lighter

Fire Texting: How to Write Secret Messages with Fire

You can buy potassium nitrate as stump remover at most home improvement stores. You can also make your own from instant cold packs and salt substitute. Make sure to properly label your jars of chemicals!

Step 1 Mix the Ink

Mix your saltpeter with a tiny amount of water until it has the consistency of a thin paint. It's okay if the mixture is clear; we want it to be invisible ink. Thinner mixtures are less visible on paper; thicker mixtures burn more ferociously.

Fire Texting: How to Write Secret Messages with Fire

The dark area is just a rust stain.

Step 2 Write the Secret Message

Write your message on the thick piece of paper with your cotton swab (or paintbrush). Start the message on the very edge of the paper; you need an easy starting point for the fire. Apply the ink generously to ensure good results. All parts of your message must be connected in one continuous line of ink. Cursive works well for this.

Fire Texting: How to Write Secret Messages with Fire

Thick papers like card stock and construction paper smolder the best.

Fire Texting: How to Write Secret Messages with Fire

Go over your design several times to ensure an even coat.

Step 3 Dry the Message

Allow the ink to dry thoroughly. Be sure to remember which edge your writing started on. It can be helpful to make a small mark with a pencil. This mixture was too thick and left a white crystal film when it dried.

Fire Texting: How to Write Secret Messages with Fire

This spiral was almost completely invisible.

Fire Texting: How to Write Secret Messages with Fire

Make sure to mark where your design meets the edge of the paper.

Fire Texting: How to Write Secret Messages with Fire

This is where you will light the ink.

Step 4 Light the Message

In a nonflammable environment, outdoors away from sentient creatures, bring a flame to the edge of the paper where your secret message begins.

The potassium nitrate embedded in the paper will smoulder and burn away your ink in the pattern of your secret message. Longer messages take a while to reveal themselves, so be patient. No one said it was instantaneous.

What secret messages will you write? There is a lot of potential for fast motion video here. If you try out this experiment, take some pictures or videos and post them up on the corkboard. If you need assistance, start a thread in the forum or message me personally. I am happy to help!

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Photo by Helmenstine


Steganography or pyrography? Both! Thanks, love your articles! I am still meaning to make that rocket in a bottle thing...hopefully will have time during spring break? :)

Thanks very much JT! Breaks are a good time for jet engines.

Very cool way to hide a secret message and I love the video. Looking forward to seeing videos of people giving this a try...

As am I! I'm sure the community will have good ideas for this one.

im sorry, i couldn't help but noticing that you had a lot of pretty deep cut marks in the middle of that lid that you were using... :D

THe lid was used in the layden cookie jar tutorial. I had to scrape off the plastic coating to make an electrical contact.

I 'm a high school junior form student and my friends and I r doing a project abt this experiment. can u tell us the theory behind this experiment ? what does it tell others about?

sigh grammar...

but this experiment was basically showing reaction times through the method of burning.
the saltpeter burns off quicker (or reacts with oxygen faster) than the surrounding paper,
which allows for the creation of visible patterns.

This is such a cool experiment! It might be a cool prom queen canidacy thing to do! It's honestly on my list btw. Haha

Thank you for posting this experiment. I do plan to use it.

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