You can use oversize shells to bring a touch of the seashore -- and a bit of romantic atmosphere -- to an evening at home. We used "lion's paw" shells (Lyropecten nodosus), available inexpensively from online auctions and souvenir shops. Fill a shallow tray with sand, arrange pairs of your prettiest specimens, and place a votive candle at the center of each pair (leaving room for the flames to flicker safely). Set the tray on a low table, and enjoy a quiet drink on the patio.
Mood Lighting
Martha Stewart Living, August 2007

If you purchase the shells, they should already be cleaned. If you've gathered shells from the beach, a soak in one gallon of plain water with 1/4 chlorine bleach should remove most gunk. Scrub with an old toothbrush for stubborn areas.
How do you clean the shells in order to use them?
joduluth: "half" means what you see in the picutre; a half looks like a little saucer from nature. for the craft you put 2 halves together, cupped side facing each other, to make the recess where the candle is placed. Should look beautiful.
they have to split them to get the scallop out right?
The shells I'm seeing online seem to only be half shells. Any source available where the entire shell is in tact?
Gorgeous
Beautiful. My trip to the beach this year, I will be finding these shells to create this at home.