Invisible Ink with

Lemon Juice

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Materials

  1. Cup

  2. Paper

  3. Lemon

  4. Q-tip/Paint Brush

  5. Lighter/Hair Dryer

 

Procedure:

  1. Cut and squeeze lemon into a cup.

  2. Soak the Q-Tip or Paint brush in the lemon juice. You'll use this to write your message. 

  3. Write your message on plain paper.

  4. Wait for it dry. DO NOT RUSH, you’ll be able to see the message as long as it wets so make sure it’s completely dry before starting the next step. 

  5. Get your heat source (you could use alternative methods such as an iron or a light bulb to get Okay results.) Hold the paper over the heat source and your message will appear! WARNING: Be careful when holding an open flame and ask an adult to help  you. 

Get lemons & prepare 

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Get lemons & prepare 

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Squeeze the cut lemons and pour juice into a cup

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Get lemons & prepare 

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Results:

The lemon juice on the paper should have reacted to the heat, and a message you’ve written should’ve shown in brown. If you heated the paper in other spots too the paper might appear a little brown or burnt due to the heat.

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Science behind this experiment:

Oxidation

Most invisible ink messages can be revealed by heating either side of the paper on which they’re written. Lemon juice – like most fruit juice – contains carbon compounds. These compounds are pretty much colorless at room temperature. When you wrote your message using the lemon juice, the carbon-based compounds were absorbed into the paper's. When you heated the paper, the heat caused some of the chemical bonds to break down, freeing the carbon. When carbon comes in contact with air (specifically oxygen), oxidation occurs and the substance turns light or dark brown. One effect of oxidation is things turn a darker color. (Some oxidation doesn’t need heat to occur; it just needs a little air. Think of a piece of apple, banana, or pear left out on a plate for a while.)

Other substances which work in the same way include orange juice, honey, milk, onion juice, vinegar and wine.

Further Experimentation

This could be conducted with different types of liquids with carbon compounds or effects like lemon juice. For example orange juice could also work. We could also change the heat source to see how much of the message shows in a set amount of time.