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http://www.sciencekids.co.nz/projects.html

Magic ink

What you need:

• lemon
• water
• small plate
• toothpick
• white paper
• lamp

Activity:

Squeeze the lemon juice into a small plate with a few drops of water and mix with a spoon.

Dip the toothpick into the lemon juice mix and write a message on the white sheet of paper.

When it dries the writing will be invisible.

Heat the paper by holding it over a lamp with the writing side down.
 
The invisable ink writing will slowly turn brown and appear on the page!