Remove Iron Staining from White Marble using a Poultice:
By Frederick M. Hueston, Stoneforensics.com
Purchase or make a poultice: You can make a poultice by mixing a commercial poultice powder with water, or you can use a homemade poultice made of ¾ cup Flour,1/4 cup Iron Out and water. Mix the poultice to a consistency similar to that of pancake batter. Iron Out can be found in the plumbing department in most home centers.
Clean the stained area: Before applying the poultice, clean the stained area of the marble with a soft cloth and a mild detergent. Rinse the area thoroughly with water and let it dry completely.
Apply the poultice: Once the marble is completely dry, apply the poultice to the stained area with a putty knife. Spread the poultice over the stain, making sure to cover it completely and extending the poultice beyond the stain by about an inch.
Cover the poultice: Once the poultice is applied, cover it with plastic wrap or a sheet of wax paper. This will help prevent the poultice from drying out too quickly and also prevent it from getting on any other surfaces.
Let the poultice dry: Leave the poultice on the stained area for at least 24 hours. The poultice will dry and draw the iron stain out of the marble.
Remove the poultice: After 24 hours, carefully remove the plastic wrap or wax paper and use a plastic scraper or putty knife to remove the dried poultice. Be careful not to scratch the surface of the marble.
Rinse the area: Once the poultice is removed, rinse the area thoroughly with water and dry it with a soft cloth.
Repeat the process: If the stain is still visible, you can repeat the poulticing process as needed until the stain is completely removed.
Note: When working with marble, be sure to test any cleaning products or methods on an inconspicuous area first to ensure that they do not damage or discolor the marble. Additionally, if you are unsure about using a poultice or do not feel comfortable doing it yourself, it is best to consult a professional stone restorer.