Kids, let's try to write a message that will appear as if by magic on paper, using chemistry. You will need a soup bowl, some tincture of iodine, a lemon, some notebook paper, a cup, and an art paintbrush.

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

Procedure: - pour 1/2 cup water into the bowl - add 10 drops of iodine to the water and stir - squeeze the juice of the lemon into the cup - cut out a smaller-than-bowl-sized section of paper - dip the art brush into the lemon juice and write a message on the paper - let the juice dry on the paper - put the paper in the iodine solution in the bowl

What happens? The paper should turn a blue-purple color everywhere except where the message was written, so that the words are outlined by a dark background. Why? When starch molecules in the paper combine with iodine, the combination is blue-purple in color. But Vitamin C (from the lemon) combines with iodine to form a colorless molecule. The area covered with lemon juice remains unchanged in color because of this.  

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Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
September 1992