Have you ever seen one of those cop shows where they shine a black light on the floor to look for blood or other evidence? The blood glows because it is faintly fluorescent--it absorbs ultraviolet light and re-emits it in a visible wavelength. But you don't need to use blood for invisible ink. There are common household chemicals that will glow under black light.
Things You'll Need
- Distilled vinegar
- Vitamin B-12 pills
- Black light
Get laundry detergent with a brightening agent. Brightening agents make clothes look brighter by fluorescing, absorbing ultraviolet light and releasing it in the visible spectrum. Mix the detergent with water. The more detergent in the mix, the brighter it will glow. See Resources below for a list of detergents that have brightening agents.
Use a paintbrush to write a message on a piece of paper and wait for it to dry. Look closely at the paper. If you can still see the writing, it is not invisible ink. Dilute the mixture with more water and try again.
Once you have ink that you can't see in normal light, write your final message on a piece of paper. Use unlined paper so that you don't give away the message by blurring the lines. Wait for the ink to dry.
Put the invisible message under a black light. Move the light closer until you can read the message. It should glow brightly.
Try using some other invisible inks. Flat tonic water is a good invisible ink, because the quinine fluoresces. You can also crush vitamin B-12 pills and mix them in distilled vinegar until they dissolve.
Tips & Warnings
- Kerosene will also work as invisible ink. It is highly flammable, however, and is not recommended.
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