what powders glow under black lights? - Instructables
This glow in the dark powder should be effective and cheap, especially when mixed with some mineral oil (sold near the laxatives). But why not use containers of nutrient gel and let them see (and smell) the actual bacteria from their hands? This would help you explain to the that some kinds of skin bacteria are good and some are bad. (Technically, 'good' and 'bad' also depends on ...