An Iowa man published a book (3 ring binder) of newspaper articles, and his research papers, about restoring cemeteries. I have a copy of his title page and his name and address somewheres, but until I re-organize, it is doubtful, I can find it. Check with Iowa's state historical society, they should know his name and address, etc. He played a part in restoring several Iowa cemeteries. I might have posted that information on the Iowa Genforum, or Kansas Genforum in 1999. He suggested that AFTER the stone is cleaned to spray a fine mist of water with a tiny amount of Clorox on them annually to prevent re-growth. I have seen a man do this when he was going around decorating on Memorial Day, by using a back pack type tank weed sprayer with wand. The author ran full strength tests(straight household Clorox)on broken chips, without any damage after months(maybe years). I don't think he mentioned it, but NEVER PUT VINEGAR ON TOMBSTONES, ESPECIALLY MARBLE AND LIMESTONE. Even in grade school, I learned that you can remove a fossil from limestone or marble etc., with vinegar. The vinegar eats away the stone. Some vinegar was spilled on our 42' marble top table while de-liming a Mr. Coffe machine, and badly damaged the surface. I will need to have the underside surfaced, and then use that surface. I had immediately wiped off the vinegar and put a damp mixture of baking soda on the table, but it was too late. VINEGAR CONTAINS UP TO 6% OF AN ACID CALLED "ACETIC ACID", I learned that from my grade school chemistry set, and chemistry class in high school. Vinegar will soak into the invisible pores of the stone and dry (into acetic acid crystals), after it does damage. Everytime it rains, it will be re-activated, and do more damage. I warned a second cousin about this, and he put it in on a tombstone anyway(one of his male ancestor's tall tower dolomite stone, that I located for him). He claimed to have RINSED the stone off. The inscriptions and symbol were deep & sharp after several decades; two or three years latter they were faint, and had rounded over edges. I have before and after photographs. People mistakenly put vinegar on grave stones, because they want to whiten them, which it does. I will report latter on methods I have used to clean and transcribe tombstones, so I can accurately read them, or photograph them; for cemetery indexing. My cleaning methods are effective and leave no visible damage, even under magnification, and entail no chemicals for cleaning, nor reading the inscriptions. I once saw pictures of upright slab gravestone on the east coast, that could be flexed like sponges, supposely due to acid rain. That might have been the case, but I often wonder if that tourist area had whiten those stone with vinegar.