Lemon Juice Invisible Writing

Here is a fun one to try.  Students are given some lemon juice and some cotton swabs.  They are given some white paper and told to write on it with the juice.

Wait for the lemon juice to completely dry.  This will make it invisible. 

Next, apply heat to the paper.  You can iron it or just hold it up to a warm light bulb.  

 The writing will appear!!!!

What's happening?

Lemon juice is an organic substance that oxidizes and turns brown when heated. Diluting the lemon juice in water makes it very hard to notice when you apply it the paper, no one will be aware of its presence until it is heated and the secret message is revealed. Other substances which work in the same way include orange juice, honey, milk, onion juice and vinegar.  

This oxidation is a chemical reaction and cannot be reversed easily.  The brown color is actually a new substance.  

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