If you're crafting with seashells you found on the beach, you will probably want to clean them first to remove any grit and to ensure they don't stink. Soak shells in a 50-50 solution of bleach and water for an hour or longer. You may also need to scrub them gently with a brush. Rinse with soap and water to remove any bleach residue and remaining dirt and grime. You can also clean seashells by adding 2 Tablespoons of baking soda and a dash of salt to 2 cups of hot water. Allow the seashells to soak to remove the grime.