what to do with egg shells?

If you start to wash your hair with egg yolks, you'll have a lot of egg shells.

DON'T THROW THEM out!!!!!!!

Especially when you use domestic eggs. You can prepare calcium citrate - a source of calcium, bioavailability of which is 2.5 times higher than in calcium carbonate as Wiki says.
More you can read hear.

So, what do you have to do?
Gather shells from about 10 eggs wash them and boil for 10-15 minutes to kill all the germs and dirt. Then take it out and try to remove the envelope which is usually on the shell inside. Don't worry if you leave some of it inside! It's not dangerous. The reason is that shell without envelope seems to dissolve faster. When done, put all shells into a jar and crumble them.

Now, time has come for lemons. Take 2 of 3 lemons, scald them and crush out juice. Then pour this juice through the sieve into the jar with crumbled egg shells. The juice has to cover them.

Put this jar into the fridge and shake it time from time. Do this for approximately a week. It can take longer time. It will then become white, just like milk.

Take it 1 spoon after meal two times a day. Listen to your body while taking it. If you notice some discomfort for your body, stop taking it.