Bring a little mystery and intrigue to your loved ones this Valentine’s Day, with a secret message that must be revealed under adult supervision.
All you need:
- white paper or white paper doily
- lemon juice
- cotton swab
All you do:
- squeeze lemon juice (use protective eye wear for safety)
- dip swab in lemon juice
- write secret message with lemon juice (invisible ink)
- include instructions to uncover the message (see below)
- give to your special Valentine
Why does natural lemon juice act as a natural invisible ink? The best explanation that I have found is from the amazing book Maker Lab by The Smithsonian. “Paper naturally turns brown with age. Lemon juice and heat speed up the process. Paper is made of a compound called cellulose. Each large molecule of cellulose is made up of thousands of smaller molecules of glucose (a type of sugar) that is bonded together. The citric acid in the lemon juice slowly weakens the bonds between the glucose molecules, freeing some of them. When the paper is heated to over 350 degrees fahrenheit, these free glucose molecules react together in a chemical process called caramelization. This produces new compounds that have a brown color and makes the ink visible.”
We had so much fun making secret Valentine’s, but this process would be great for invisible ink messages year round. It would be tons of fun to make secret treasure maps, or secret messages for a spy themed party… Other heat sources could be used, like a hot iron, or a hair dryer on high. Happy Valentine’s Day!
Amber is an art teacher who has a process approach to teaching, with a focus on STEAM (Science, Technology, Engineering, Art, and Math) education. You can follow her on Instagram, Facebook, Pinterest, and Twitter.
Check out our new Valentine’s Day Ebook http://steamkidsbooks.com/steam-kids-valentines-day/?ref=5