We recently surveyed a cemetery here in Austin, TX and the one old stone we were looking for, we found but it was illegible. We ever so gently rubbed the surface with chalk and could then read the homemade stone. My brother-in-law was thrilled, as they were from his family and people had been looking for a long time for that stone and we luckily found it. Eventually the chalks wears away and no harm is done to the stone. Linda