Invisible description

Exploration Stage: Collector's House
From: Detective
Description: I'm thinking, if the secret society the collector started was doing something clandestine, all the descriptions about it would be in invisible ink. If we could find such ink and find out how it works, we might be able to figure out how to read what was written. Would you be willing to go into town and look for invisible ink?
Completed: You found invisible ink! Let's check it out right away... see, the letters you drew on your notebook disappeared right away. There's an instruction on the back of the inkwell. It says you'll need a special exposure solution to make the letters appear again.