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Metal stains (iron, rust, copper, bronze) must be removed with a poultice (liquid cleaner or chemical mixed with a white absorbent material to form a paste like the consistency of peanut butter). Deep-seated, rusty stains are extremely difficult to remove, and the stone may be permanently stained.


Iron or rust stains are orange to brown in color and follow the shape of the staining object, such as nails, bolts, screws, cans, flower pots, and metal furniture. Copper and bronze stains appear as green or muddy-brown and result from the action of moisture on nearby or embedded bronze, copper, or brass items.