Introduction: Write Secret Messages With Invisible Ink!

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Have you ever wanted to write secret messages to your friends? There’s no better time than now, with this easy-to-follow recipe (w/easy-to-follow Science, too)!



  • 1 (or 2) Lemons (or bottled lemon juice)
  • · Bowl (or another container to put the lemon juice in)
  • · Cotton Swabs (or toothpick, wooden skewer, or other item to use as a writing instrument/stylus)
  • · 1 (or more) pieces of white Paper (how many messages would you like to write?)
  • · Toaster Oven (or another heat source, such as a glass top stove, or lit candle)*

*Be sure to have an adult help you with your heat source!!*

  • · Oven Mitt
  • · Kitchen Knife

*Be sure to have your adult handle the knife and the cutting!!*

Step 1: Use the Kitchen Knife to Cut the Lemon in Half. *Be Sure to Ask an Adult to Help You With the Cutting!!*

Step 2: Squeeze Each Lemon Half Into the Bowl.

This lemon juice, including the citric acid and carbon it contains, will be the ink to write your secret message!

Step 3: ​Use a Cotton Swab, or Toothpick As a Writing Instrument/stylus

Do this step by dipping one end of the swab into the lemon juice and using that same end to write your secret message on a piece of paper. It won’t take a lot of the concentrated lemon juice to create your message!

Let the lemon juice dry on the paper as the lemon juice is absorbed into the paper fibers.

Step 4: Place Paper in Oven

While the lemon juice is drying, preheat the toaster oven to 350 degrees (Fahrenheit). The heat from the oven will cause the citric acid in the lemon to break down at a faster rate, freeing some of the carbon in the juice.

Turn the toaster oven off and place the paper with the message on it inside. *Be sure your adult uses an oven mitt to place the paper inside the toaster oven*

*Watch the paper in the oven to make sure it doesn’t burn. *

Once the carbon came into contact with the air, it went through a process called oxidation, one effect of which is to turn a darker color.

Step 5: Remove Paper and View Message

After 3 – 4 minutes, remove the paper from the toaster oven. When the carbon was freed from the lemon juice and came into contact with the air it went through a process called oxidation, which turned it a darker color than the rest of the paper. In oxidation, the lemon juice lost electrons to the air around it when it gained oxygen. This is the same process that happens to apples and pears when they turn brown after you cut off a slice and leave it out on the counter for too long!

*Be sure your adult is using an oven mitt to remove the paper from the toaster oven!

Your secret message should be revealed! Repeat the steps and share a secret (and the process) with a friend.