Wash empty eggshells in warm water until all of the egg white is removed, but do not remove the membrane because it contains important nutrients for the joints which helps arthritis.
Lay broken pieces out on paper towels and allow them to air dry thoroughly.
Break the eggshells up into small pieces, and grind them to into a fine powder in a food processor, blender, coffee grinder, or a nut mill, or put them in a plastic bag and use a rolling pin to grind them. Please note that some blenders will not grind the eggshell into a fine enough powder. A coffee grinder works the best.
Store powdered eggshells in a covered glass jar or container. Keep it in a dry place, like the kitchen cupboard.