Calling All Secret Agents...Let's Make Some Invisible Ink!

You will need:

• Bowl
• Spoon
• White Paper
• 1/2 a lemon, or lemon juice
• Water
• Cotton Q-tip
• Lamp/Light bulb

Directions:

1. Squeeze the lemon juice into a bowl. 
2. Mix in a few drops of water. Stir with spoon.
3. Dip the Q-tip into the juice. 
4. Write your secret message on the paper.
5. Allow to dry.
6. Once it is dry and you are ready to see your message, hold the paper close to a light bulb (or other heat source). Your message will appear!

         Note: I tried it with a light bulb and couldn't get it to work. I ended up sticking the papers in the oven at 225 degrees F. It can take awhile for the message to appear. You need to watch carefully so the papers don't get too hot and burn!

Hypothesis and Observations:

• Why does the message appear near a hot light bulb? (When heated, lemon juice oxidizes and turns brown.)
• What else could you use to create invisible ink? (Onion juice, vinegar, wine, orange juice, milk, honey dissolved in water, syrup dissolved in water, equal parts baking soda and water mixed together.)
• Why do you add water to the juice? (It dilutes the juice and makes it harder to see on the paper.)

Milk & Onion Juice

Baking Soda & Water Mix
Note: I mixed them together, but it
created a fine sandy film where I wrote
wrote the letters. Maybe, if you let the
baking soda dissolve in the water
longer, it would not show up.

Honey & Water Mix

Option 2: Blacklight Ink

Mix laundry detergent (one with a whitening agent) with water. You want to get it to about water thickness. The thicker it is, the better it will show up under blacklight. However, it you make it too thick, it will show up  in regular light as well. To test your detergent/soap, mix with water in a clear jar. Turn out the lights and hold by the blacklight. It should glow. (Some dish soap might work as well. If you aren't grossed out by it, saliva sometimes works too.) Using a paint brush, write a message on dark paper (white paper will glow under the blacklight too). Let dry. Reveal your message by holding near the blacklight! (Note: I found that a cardstock type of paper worked better than construction paper at showing up the message.)