How to use eggshells for calcium supplement in potting mix?

[Dr. Dave 4u]

First, I wish to thank everyone who has responded to my beginner questions....it's been very helpful...thanks again!

OK, I'm asking about using eggshells for indoor orchids.

I have been watching some videos and searching the posts on here about using egg shells for a mineral supplement. I kind of like the idea to recycle them but is it really a good idea?

My questions are as follows....

- If they are from hard boiled eggs they would be sterilized, correct?- Some folk recommend*you bake the shells at 300 for about 20 min, is this necessary?

- What about the membranes on the inside of the shell....would they cause problems with any indoor pests, bugs, FUNGUS GNATS etc? If so, the best way to remove the membranes?

- Some say grind them coarsely with mortar and pestle and work into your potting mix, some say grind to fine powder in spice grinder and shake on a few times per year. I assume the coarser grind would hold more in the potting mix and the powder wash through? Thoughts?

- How much eggshell per orchid would be good to use?
Say in a quart of orchid mix how many Tbsp's would you suggest?