You must watch this:
I'm sorry it's just a link, I tried to embed the video (I even searched on how to do it!) but the code isn't working for some reason. At any rate, this is a guy doing an awesome job marbling paper, something that I learned about in my Paper in the Scholarly World class. You need (as you can see) a tray for the water which has been treated with (usually) something called carrigeenan, which comes from a plant. Then you can drip pigments/paints which have been treated with oxgall (literally stuff that comes from the gall bladder of an ox....appetizing, no? lol) onto the water, where they will float. You can then use various tools, combs, etc. to manipulate the pigments to make cool designs, then gently place a piece of paper that has been treated with allum (another chemical) onto the top of the water. Ta-da, marbled paper! It's often used to cover the boards of books, and/or as endsheets on books.
In somewhat related news, I just started my bookbinding class today and I. Love. It. so much! :) There will be many pictures and a big post to come at the end of the week. I know, you're all really excited to hear more dorky book stuff, don't all tell me at once. hehehe :)