Eggshells are normally discarded and their intrinsic value as a potential contributor of calcium to diets is ignored.  In the E.U. and Japan some consumers preserve the shells of hard-boiled eggs for consumption or for other applications. 

It is recommended that eggshells should be harvested after at least five minutes of boiling to ensure that any potential pathogens are destroyed.  Some consumers bake eggshells for up to 10 minutes at 180 F although this is condidered unnecessary.  After removal shell fragments can be reduced to a fine powder in a coffee grinder.  This can be incorporated in smoothies, sprinkled on pizzas or other foods as a topping.  Some consumers add fine shell particles to bird feeders during summer to supplement diets with calcium required by nesting birds.