Posted 23 July 2015 - 03:30
Thanks! I will have to check these out. If they are natural, there is no reason they shouldn't be perfectly good. China's a big place and likely has the rught rock simewhere. Even today, if you know the places to look, you can harvest your own from rock formations in the wild (E.g. I know some places in Edgefield county, SC). Some were sources for commercial stones into the early 1900s.
If you feel they need truing to assure flatness, get a small section of plate glass (be sure to tape or grind those sharp edges!) and place some abrasive wet-and-dry paper on it with spray adhesive. Then grind the stone with water or oil. Plate glass is truly flat and isn't expensive in small sections (try a Lowe's or Home Depot).
Woodworkers use this trick to true and polish the bottom of a plane, as well as sharpen the blades.