Haven't you always wanted some invisible ink for secret spy missions as a kid? Well it's not just for spies! Acorn Invisible Ink is both waterproof and safe to use on skin. Most commonly applied to hands and arms for identification purposes at gatherings, night clubs and parties, our UV invisible ink dries instantly and can remain on the skin for approximately 24 hours. Acorn Invisible Ink shows up as BLUE when seen under UV lighting. A dry ink pad must be purchased to use our invisible ink with a regular rubber hand stamp.