I agree not to use graphite on stones..reason being: on a nature walk with our local Audubon Soc. the biology major pointed out the green reed , often seen growing alongside railroads, which she said the pioneers used to scrub their cooking pots with because it contained graphite......Also the current manual for the 4H genealogy project in Indiana, on page 13, contains this info pertaining to reading stones:"cleaning with steel wool, wire brush, whisk broom, .be very careful with the wire brush. Some old stones are best rubbed with chalk, white vinegar and baking soda does a tremendous job in cleaning other stones.".. ruth pride wheatland,in