For me once I save an egg shell, I will wash it under running water first to get rid and traces of egg. In a small bowl, pour hot boiling water use a small toothbrush to gently brush the whole egg shell, inside and out. (I always get my eggs fresh from the market so no ink stamp) If egg shell have ink stamp must peel off. I have a basket next to my kitchen window where I keep my egg shells to let them sun and air dry.
Once I collected about 20 or so, First step is to boil them at high heat. Submerge the egg shells entirely with water in a pot add the juice of half a lemon ( to get rid of the smell ) and let the whole batch boil on the stove on high heat for 30 minutes. A while foam will form during the first few minutes. Use a ladle to get rid of the white foam. By the end of 30 min there must be no white foam present. The white foam is actually all the dirty particles we want to get rid off.
After boiling I strain the egg shells. Spread them out onto a tray to air dry before baking them at 200 degrees for another 30 mins.
After baking the egg shells should be very dry and crispy.
After the egg shells cool, I blend them in my Miller until very very very fine.
Store in a air tight container in the fridge.
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