Invisible Ink

I'm working on a project with invisible ink (you can only see it with a blacklight)... here are some quick tests:







The ink is water soluble and you can do light washes, but you're pretty much limited to two or three tones...with a really light touch. Everything after that gets muddled together. Also, if you over do it, a thin yellow film builds up on the paper, pretty much defeating the purpose of invisible ink.
I bought it from Jet Pens
they're really good