Remove inner membrane from all the shells.
Break shells into small pieces.
Lightly roast the shells in a frying pan until brown. Do this slowly over the course of about 45 min, stirring frequently. Do not char them until black. You simply want to remove the organic substances that could rot the entire batch.
Put1 part of the crushed eggshells to 10 parts brown rice vinegar into a clean,half gallon-sized mason jar, but only fill 2/3 of it.
Cover with paper towel or other breathable cloth or paper tied with string. You can use rubber bands, of course, but I've occasionally had some pop while I wasn't looking. It will be bubbly and active at first like soda. After about a week or so, when it stops moving.
To confirm the brew is ready, add a little of your extra toasted eggshell. If it does not produce new bubbles, you can strain off the vinegar.
Store in a cool dark place in bottles that are not tightly closed. It must breathe. Overly tightened bottles have been known to explode over time. You have been warned.
Be sure to label what's in the bottle, including the date of extraction and dilution ratio, which is 1:1000.
Water-soluble calcium percolatesfor about 7 days