That just happened to me the other day. I was going to drop some concentrated liquid watercolor onto some rice paper for some colors I wanted to be using in my paper paintings.
The weather has been ugly, so I was doing it in my art room but needed something good and waterproof to put the rice paper on.
I had been given some wallpaper books quite a while ago that were these rather large sheets of vinyl wallpaper. I decided to use those.
I turned the wallpaper over so the most coated side was down, protecting the table surface. Then I got nice and messy with the watercolors. When I was done, I left the room to let them dry.
When I returned and started to pick the rice paper up...the wallpaper was almost as beautiful as the paper I had actually intended to paint!! I couldn't get over it. The colors blended sooo beautifully that, instead of it being something merely to protect my surface, it became something that I just NEEDED to use as well.
Sooo....that was when I decided to make an envelope out of it for the latest mail art swap. The theme for this one was "transportation"...and I think this will work out perfectly.
Don't you just love a happy accident!?!