Question: is hydrogen peroxide safe on natural stone?
Answer: Metal stains must be removed with a poultice. (See section on Making & Using a Poultice) Deep-seated, rusty stains are extremely difficult to remove and the stone may be permanently stained. Clean with diluted (1/2 cup in a gallon of water) ammonia OR bleach OR hydrogen peroxide. DO NOT MIX BLEACH AND AMMONIA!