the secret's out

How cool would it be to receive an invite to an event with instructions that to magically uncover the content of the invite you need to hold it over a light bulb. And when you do, slowly, a secret message begins to appear before your eyes. Sounds a little like something out of a Sherlock Holmes novel. But it’s actually made possible by a company called J. Herbin (the oldest name in ink production in the world).
Their Invisible Ink, which retails for about $16 USD, comes in a 30mL bottle. The ink looks pink in the bottle, but it goes down clear.