I don't drink coffee, but dh does and I mentioned to him that I wanted to use his left over coffee and grounds if he was through with them. He was, but was very curious about WHAT I wanted them for - boy, was he surprised when I "stamped" the coffee using a glass, then dumped the grounds on the pages and smooshed them around.
Once this was dry (which took longer than I imagined), I dusted off the grounds and the pages looked like this.
Here's a closeup of them. Not really the look I wanted.
Plan B: splatter paint on the pages. I dumped some acrylic paint in a small glass and added a little bit of water to make it runny. Then I took the handle of a paint brush, dipped it in the paint, and slung it out over the pages. I like the look I got with this!
Here's a closeup!
Now I have to add a smudged stamp image on the back, along with my contact info and these are ready to go in the mail (after they dry, of course).