Lemon Juice or Milk Ink

What You Need

• Q-tips Cotton Swab
• Lemon juice or milk
• Paper
• Electric iron
• Ironing board

What to Do
Using the Q-tips Cotton Swab as a paintbrush and the lemon juice or milk as ink, write your message on the paper. Let dry at room temperature. With adult supervision, iron the piece of paper.

What Happens
The invisible message appears.

Why It Works
Lemon juice and milk are simple organic liquids that appear invisible once they have dried on a sheet of paper, but darken when held over a heat source.

Bizarre Facts

• Prisoners of war used their own sweat and saliva as invisible ink.
• India ink was actually invented in China.
• During World War II, a German spy named Oswald Job was executed in 1944 after a crystal of concentrated invisible ink was found hidden in a hollow key.

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