"How to Make Powdered Eggshells: 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. Lay clean 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, and keep it in a dry place, like the kitchen cupboard. How to Take Eggshell Calcium: There are two ways of taking eggshell calcium: Option #1: Take the dry powdered eggshell without mixing it with lemon juice. Since it is high in minerals they won’t mixed into any liquids because they will sink to the bottom and you’ll be digging it out with a spoon. Instead put the correct amount on a dessert spoon, add some warm water and mix it as best you can, and take it from the spoon, followed by swallows of water. Option #2: Soak the eggshell in lemon juice as instructed below. You can make more than one dose at a time but after soaking it in lemon juice keep it in a tightly covered glass container in the refrigerator so it won’t dry out. Put 1/2 teaspoon of powdered eggshell into a small dish (approximately 4 1/2 to 5 1/2 inches across) – 1/2 teaspoon equals approximately 400 mgs of elemental calcium. Add the juice of 1/2 a lemon (freshly squeezed), and mix well–it will start to bubble and foam, which is what is supposed to happen. Leave it at room temperature for 6 hours – the longer you leave it the less gritty it will be, but do not leave it longer than 12 hours since it will dry out too much. Take it from a spoon, followed by mouthfuls of water to wash it down, and always at mealtime. It is not sour tasting. In fact the taste is quite pleasant. Also take 400 mgs of magnesium citrate at the same time."
So I found this online—making your own calcium supplement from grinding up dried eggshells…which apparently can double as a face powder. Ick or awesome?
Calcium Made From Eggshells