You've bought oysters, used them and now have several oyster shells left over. Instead of just throwing them in the trash, find another use for them. Reuse the oyster shells by crushing them and using them in crafts, as an addition in gardening soil or in aquariums to adjust the pH balance of the water. Crushing the shells can be be done rather quickly.
Boil the oyster shells for a few minutes to kill any remaining bacteria.
Take the shells out and let them dry.
Place a few of the dried oyster shells in a plastic zip top bag and seal. You want the oyster shells to lay flat in the bag. Make sure you've gotten most of the air out of the bag.
Put a towel over the bag. This will help keep the oyster shells in place if the plastic bag punctures.
Hit the towel that's over the bag with a hammer. Do this until you've reached the crushed consistency that you want.
Take out the shells and place them into a mesh sifter. Push the shells into the sifter if you want a finer consistency. For even finer consistency, place the shells into a mortar and pestle and grind.