Check out this information brought to our attention by Jan Ramos. This is the web site for the Association for Gravestone Studies with emphasis on care, art, importance, symbolism, & more. http://www.gravestonestudies.org
The word needs to get out - plain water and soft brushes only for old stones. No chemicals, no power washing (which is what the pros love to use - not only does it cause physical damage, but it can change the color of the stone!).