I use their egg shells as well. We have a bowl in the fridge and when someone makes eggs, they put the shells in the bowl( broken in pcs), when the bowl gets full, I put in microwave for a few mins to cook any raw egg still on them and transfer to a Qt jar in the fridge. I put their shells in a separate dish so they can use as needed.Seems to work great, usually when their out of shells, I have a bowl in the house ready to go. I have a bag of oyster shell that I've only had to dip in 1 time when I didn't have enuf egg shells.