Create your own spy tool by making a secret ink pen that only reveals its messages under a UV light. You'll learn about fluorescence and how certain substances react to ultraviolet light!

Tools

• small mixing bowl
• stirring spoon
• scissors
• empty marker or felt-tip pen (1)

Materials

• tonic water containing quinine (1/2 cup)
• distilled water (1/4 cup)
• clear glue or cornstarch (1 tsp)
• UV flashlight or blacklight (1)
• white cardstock or paper (5 sheets)

Safety

• Adult supervision required when handling the UV flashlight to avoid looking directly into the light source.
• Be careful when using scissors to disassemble the pen.
• Adult supervision required for sharp objects.
• Protect work surface. Materials may stain clothing.

Steps

1. Carefully disassemble your empty marker or felt-tip pen by removing the back cap and pulling out the ink reservoir/felt core.
2. In a small mixing bowl, combine 1/2 cup of tonic water and 1/4 cup of distilled water. Stir gently.
3. Add 1 teaspoon of clear glue or cornstarch to the mixture and stir until smooth; this helps the ink adhere better to the paper.
4. Place the felt core of the pen into the mixture and let it soak for about 10 minutes to ensure it is fully saturated with the 'invisible' ink.
5. Slide the felt core back into the pen casing and replace the cap securely.
6. Write a secret message on a piece of white cardstock and let it dry completely until the writing disappears.
7. Turn off the room lights and shine your UV flashlight over the paper to reveal the hidden message!