Science experiments for kids – Water fluorescent – You can use a highlighter pen (yellow, green and pink are the ones that work best) to create an invisible fluorescent solution, which appears under a UV light or, of course, a black light lamp.
Just remove the cartridge inside of a marker, Comminute and soak it in water for a few hours.
http://www.sciencecompany.com/Torches uv cheapest are those that are used for fishing or to track the urine of Pets animal; of course it is not an activity for young children and should be taught how to safely operate the torch.
____________________________________The liquid obtained can be used to write secret messages that appear only in the light uv. The experiment works, of course, also using “black light” bulbs.