I'm pretty sure this is where I learned to use lemon juice as invisible ink. Let it dry, and then hold it over a flame and the places where you wrote with the lemon juice turns brown--leaving most of the paper sort of white.

That said, a friend of mine was doing this in his room and set the paper on fire. His mother smelled it and came running in to see what was burning. She then proceeded to accuse him of trying to burn his stash of lascivious literature and magazines. We, as guys will, never let him live it down.
Later on he died a sad and very young death. The family had him cremated and his ashes were kept on the mantle piece in their living-room.

Whenever we were over at the house visiting his brother, the lid of the box of ashes would get lifted and some wags would flick their cigarette ashes in there----and then loudly proclaim that: "Jeez, Bill seems to be gaining weight!"

A fine time was had by all.

And maybe we should thank Mr. Wizard!?

Art