How to Make an Invisible Trail?
I am trying to make a hidden trail that can only be followed with a black light. This will essentially be done by following a series of "bread crumbs" that are only visible in the UV spectrum. I've had some success with a highlighter; the bark soaks up the ink, making it invisible to the naked eye. It's lasted a few rainy days, but I am not certain it will last for (at least) several months. I was wondering if there is another way to do this, one that is a little more weatherproof.