You can write on slime with a UV flashlight! Make your favorite slime and mix in a 1/2 teaspoon of photo-chromic powder before you add your activator (borax or saline solution or stayflo). Stir well!
After writing on our slime we decided to make a "disappearing graffiti wall" for a party. To do this you need to spray your poster boards with adhesive and then sprinkle the powder. We then covered the boards with clear contact paper for protection.
You can add photochromic powder to certain paints and liquids but its a bit harder to predict results and you'll need a lot more. What else can you think of? At camp this week we're going to design some photochromic gadgets so stay tuned!
How does it work?
Photochromic means "light sensitive." The pigment powder we're using has a molecular structure that changes when it is exposed to ultraviolet light. The molecules basically soak up the light and in a sense block it making a dark imprint where the light was pointed/shined. If you take away the light the molecules will expand again. You see this same technology in products like tinted windows or eye glass lenses and lots of fun stuff like stickers, decorations and t-shirts.