Egg Shells

Unsterilized eggshells may contain harmful Salmonella bacteria. Before providing eggshells, boil them for 10 minutes or heat them in the oven for 20 minutes at 250° F. Let the eggshells cool, then crush them into pieces smaller than a dime. Offer the eggshells in a dish or on a low platform feeder

http://www.birds.cornell.edu/pfw/AboutBirdsandFeeding/BirdFoods.htm

You can also put egg shells in the microwave for 3 minutes to kill salmonella. When I boil their eggs I just crush the egg shell with the boiled egg and give it to my finches. But if the shells are raw then you need to microwave. FinchG