How to Make UV Invisible Ink
Many things can glow in the dark, but most of them are visible in the light as well. Invisible ink is any liquid that can not be seen in normal daylight, but glows brightly under ultraviolet light. A good spy will quickly learn that having invisible ink alone isn't enough. You have to write carefully without spilling any ink, or else people will notice the water stains on the page and get suspicious.
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Instructions
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Get a powder brightener such as the one linked to below.
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Get a small cup of water. Sprinkle in a few pinches of the ink and mix it with a spoon.
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Turn off the room lights and look at the ink under a black light. It should glow. If it isn't bright enough for your taste, add a bit more brightener and look at it under the black light again.
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Use a thin brush to write a message in invisible ink on an unlined sheet of paper. Wait for the ink to dry and look at it under a normal light. It should be very hard to see anything in normal light. If it is too easy to see, add water to the ink and try again.
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Look at the message under a black light. You should be able to read the message.
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Tips & Warnings
Saliva will also shine under a UV lamp. If you have to write an emergency message and don't have any brightener, use your spit.
