There are a couple of ways you get science projects to glow in the dark. You can use glow-in-the-dark paint, which is phosphorescent and glows anywhere from a few minutes to a few hours. Glowing paint or powder tends not to be very soluble, so it is good for some projects and not others. Tonic water glows very brightly when exposed to black light and is great for edible projects. Fluorescent dye is another option for a bright effect under a black light. You can extract non-toxic fluorescent dye from a highlighter pen to make glowing water:
- Use a knife to (carefully) cut a highlighter pen in half. It's a pretty simple steak knife and cutting board procedure.
- Pull out the ink-soaked felt that is inside the pen.
- Soak the felt in a small quantity of water. I made a video of what to expect.
Once you have the dye you can add it to more water to make glowing fountains, grow certain types of glowing crystals, make glowing bubbles, and use it for many other water-based projects.