After many years of doing my own genealogyI spend many hours Recording, Restoring, Beautify, monuments in the Jefferson, Lewis, St. Lawrence, Oswego Counties. All enzymatic agents are approved for cleaning all stones It is even used in museums and Arlington National Cemetery. It takes approximately twenty four months and repeated applications to complete process. A virtual cemetery is listed to observe the progress of each stone.
Below a link to read an article on the cleaning process