Did you use invisible ink when you were a Sixties or Seventies nipper?
I know I did. I used to love writing secret messages and revealing them somehow.
Not sure at all anymore how I revealed my messages though! Did you have to wait till it dried?
I seem to remember a particular toy that included invisible ink. There wasn't any in my favourite spy case Secret Sam though I don't think.
Could it have been those Witch shaped thick felt pens? They had plastic witches pointed hats on them.
Did you use invisible ink? Could it be manufactured at home?