I learned that Obama's sister Auma went to the same university as me.
Powdered white chalk dusted over the inscription will sometimes make it legible.
If you can, brush off all the dirt and growth, but be careful - some stones begin to disintegrate with weather and ageOn inside grave-stones I have used a special type of wax crayon (not a pencil) on a soft white paper and done a rubbing.
I use like brown wrapping paper that works better than aluminum foilthen use the side of a pencil and rub across until the words show throughIt won't be perfect but it should be legible.
I learnt that the very first food eaten by a U.S astronaut in outer space was applesauce which was prepared along with aluminum tubes of beef stew.
