The material that makes something glow-in-the-dark is not suitable for use in tattooing. Something will glow in the dark because it has phosphorescence in it. That material can cause cancer in humans. I have heard that there is safe blacklight tattoo ink, however, a tattoo is permanent, and people have only been using the blacklight ink for a few years. There is no real understanding about the long-term effects. Most of the blacklight ink that I have seen does not look very good as a tattoo anyway. It seems like that ink is much more likely to heal up patchy. No one really knows how long the ink will stay reactive to blacklight. I really cannot recommend something that has that many unknown variables.