If you want to make your own stationery and have a lot of shells and pebbles laying around try this project courtesy of www.marthastewart.com.
The verbiage below is taken directly from Martha’s website:
Decorate stationery, postcards, or a travel journal using tokens collected on a recent trip.
Lay shells or stones on thick paper, and spray the area with watered-down paint. Abstract patterns emerge on the paper underneath, recalling a dappled sky.
Sprayed Stationery How-To:
1. Cover your work surface.
2. Add 1 teaspoon acrylic paint to a small spray bottle. Fill halfway with water; shake to mix. (For a more translucent solution, add more water.)
3. Arrange shells or pebbles on note cards or another paper item.
4. Spray paint mixture over shells or pebbles. Let dry for about 30 minutes before lifting objects.
Tip: Card stock or other thick paper works best; it's less likely to warp.