• Use lemon juice and a paint brush to make designs or words on paper.
• Allow it to dry.
• When you want to see the invisible message brush a dilute solution of iodine and water on the paper.

The iodine will complex with the starch in the paper and turn purple. The lemon juice painted sections will remain white. Caution: Iodine will stain almost anything it touches brown and is not an easy stain to remove.

Don't have any Iodine? Try this:

PREDICT: Ask your students "What will happen when I take this blank piece of paper and heat it over this candle flame?" OBSERVE: Watch what happens with careful heating EXPLAIN: What does this show us? (seniors might like to consider the chemical changes involved or consider carrying out a titration that uses Iodine)

Children must be very be careful and ask the help of an adult to do this!

Want to try something else? Try making a "normal" ink from tea...

1. Find out more about how people first kept records (stone tablets, papyrus, cloth, etc)
2. Did they use the same languages, or symbols (what are runes, hieroglyphics, etc)?
3. What secret codes did people use thousands of years ago, or during the war (the Enigma Machine)
4. Make up your own secret code system!