How do you know when you've run out of invisible ink?!
Question:
How do you know when you've run out of invisible ink?
Answers:
when you shine the black light (even though now that i think about it it should be called blue light, as its really blue ish purple) onto the place where you 'wrote' something with invisible ink, because invisible ink is made to show up in black (blue purple) light, and nothing appears. Then you know it has run out. Or when you pass your secret message onto your friend saying that he should step back quickly because a piano is about to fall from the roof, and he just stares at the paper with his black (blue purple) light shining on it, as a piano drops...