Hi Carter57,
Poster #2 here ChickenSahib may be referring to my process-- I do microwave the egg shells -- and then put between two paper plates and crush with a can of pineapple tidbits (just because it is there on the shelf, any crusher would work, of course). First the flat bottom, then use it like a rolling pin, resuffle and reroll until they get as small as I want them.
I microwave on high for 1 minute 30 seconds-- Just becase that is three taps on my microwave controls. My objective is to kill any bacteria, thinking samonella, that could be there. Lots of posters in another forum thought that was over kill (Literally ;O) ) The shells are kind of crunchy and they crush easily---the whites that remain are also cooked and dry so there isn't a gluey mess...
When they are crushed to flakes, about the same size as the pieces of oyster shell that I have for them, I dump in the cage cup where I keep oyster shell.
I used to put egg shells in the compost--but they took a really long long long time to decompose. I like the chicken method better. Why waste? Chickens need the calcium anyway. Because they are crushed I don't think that the chickens would tie them back to their eggs. (who really knows what goes on in those chicken brains?)
Luckily for me, I have frequent access to gather eggs...so there is not much opportunity for the chicken to get too interested in her egg.