Imagine getting a secret note which only you can read. I would love that. As I was researching about this, I read that spies used lemon juice, milk, vinegar, onion juice or even urine as an invisible ink during the 1st World War. Low tech intelligence, I guess.
Try this fun experiment with your child with all the ingredients from your kitchen pantry.
Any one of these or all:
- lemon juice
- 1 tbsp Baking soda mixed with 2 tbsp water
cotton swab/ Q tips
heat source – lamp, iron box, or a flame (Use with caution)
Step 1: Dip the cotton swab in any of ingredients (lemon juice, vinegar, milk or baking soda solution)
Write with it on the piece of paper. Let it dry. I left it to dry and went back to it in an hour.
Step 2: Under parental guidance only
If using the light bulb, turn it on and let it heat up. I found using the iron box was easier.
light bulb: Hold it over the lightbulb for a few minutes and watch your secret message appear. Be careful not to burn the paper.
iron: Place paper between two pieces of cloth and iron.
open flame: Hold over an open flame and watch the message appear.
The science behind the experiment:
Most of the ingredients given are acidic except for baking soda. With baking soda, you can paint the paper over with grape juice. The color of the writing changes. This is because the acid (grape juice) reacts with the baking soda (a base) to discolor the paper.
Lemon juice, milk, and vinegar are acidic. The acid weakens the fibers of the paper. When heated, some of the chemical bonds break down and carbon is released. When carbon comes in contact with air (oxygen), the carbon in the paper oxidizes and turns brown. (A cut piece of apple also oxidizes (turns brown) but without heating)