Marble is a beautiful stone used in construction when a builder or home designer wants to combine elegance with durability. Unfortunately, it is also a soft stone that is vulnerable to damages and stains. The somewhat oily residue of soot can be especially difficult to remove from marble, leaving many grand old fireplace surrounds looking dirty and aged. Though it may take more than one try, you can clean soot from marble and return the gleam to the marble finishes in your home.
Put on your rubber gloves and use wet paper towels to remove as much of the surface stain as possible.
Soak a sponge and/or a soft bristled brush in hydrogen peroxide and use it to wipe off the stain. Rinse the sponge or brush in a bucket of hot water when it becomes soiled. It may take several attempts to completely remove the soot from the marble. If this method is not enough to give the cleaning results you want, consider using a cleaning poultice.
Use a commercial poultice product or hydrogen peroxide to soak the stains. If using a commercial product, follow the manufacturer's instructions for mixing and applying the product. Generally, a poultice is a thick paste that is applied to the stain and allowed to sit for a long period of time. To make a poultice from hydrogen peroxide, soak paper towels in hydrogen peroxide and lay them on the stained marble. Whatever product you use, a poultice should be covered in plastic which is taped in place to keep the poultice from drying out to quickly and allowed to set for 24 to 48 hours.
Remove the tape, plastic and poultice. Wipe with a clean cloth and hot water. For particularly bad soot stains the poultice may need to be reapplied several times.