There is a tombstone list online and it has a lot of information on the care and keeping of tombstones. You, alone, chalking it might do minimum damage ( abrasion) but if all the decendants did it,.... well, you can see this is not good. Take a bottle of pure water wiht a spray top. Spray the stone and let it dry on the top surface and the wet carving will show up in a photo. You may need to take them sometime other than high noon to get shadowing, but early morning and late evening make the inscriptions stand out wiht nothing but changes of light. 400 speed film makes the best pictures of gravestones. Cacky