In an earlier email, I mentioned using bleach to clean some grave stones. I've just come across a site that seems to have a better handle on avoiding damage to stones. It states that Bleach should not be used, and recommends a number of other cleaning agents. The site is http://www.gravestonestudies.org/faq.htm#Some%20Gravestone%20Rubbings%20Dos%20and%20Don'ts If you can't copy this url into your address line, you might go to the site http://www.gravestonestudies.org/ and then select the hyperlink 'Research Clearing House', then the link 'Preservation', then the link "More Information FAQ' (at the bottom of the page), then the following FAQ: a.. Gravestone Rubbing Dos and Don'ts a.. Selected Brand Name Materials for Cleaning Gravestones- by Tracy C. Walther (Architectural Conservator) a.. Tools and Materials- by Fannin Lehner Preservation Consultants Household ammonia is recommended (One cup ammonia to one gallon water), but you should wash the stone afterwards.. The product Photo-Flo-Kodak is recommended. Also some specialized cleaning products available at swimming pool suppliers.