Have you ever wanted to play secret agent or send a secret message? You absolutely can with homemade invisible ink.
You just need a few common kitchen ingredients to make your own invisible ink. The ink in this activity will stay invisible until you activate it with heat.
You can use invisible ink in just 3 simple steps:
First, make an invisible ink made from lemon juice, apple juice, honey and water, sugar and water, or milk.
Second, apply your ink to paper using a toothpick, cotton ball or cotton swab, or paint brushes.
Third, heat up your paper (always use heat safety!).
We tried a few different heat sources: heating pad, hot cookie sheet, and directly in the oven at a low temperature (about 200 degrees). The oven worked best. You can also use a lamp, iron, or hair dryer to heat your ink.
After your ink has been heated, your secret message should appear.
Here’s how it works:
Lemon juice and apple juice oxidize and turn brown when they’re heated. This is the same reason that apple slices turn brown when they’re left out.
The water from the honey and sugar solutions evaporates and leaves behind the sugar and honey to caramelize in the heat.
The lactose in milk dehydrates in the heat and turns brown.
Who knew that you could be a secret agent in your very own kitchen?
Want more cool science? Join the free Trailblazer Club for more science activities like the Make a Crystal Experiment, Starry Art and Facts, and Animal Charts. These activities feature Ribbons & Robots characters, fun science facts, and printable activities.