An oil-stained area will darken the stone. Oil stains are caused by butter, milk, cream, salad oils, cosmetics or mustard for example. The oil or petroleum which has penetrated the surface needs to be dissolved or “broken-down”. Water soluble additives are not strong enough to dissolve oil and a stronger poultice additive is necessary.
In order to remove this type of stain, an acetone or solvent poultice must be used. Make sure the solvent is pH balanced so that it does not affect the finish of the stone. Additionally, the area should be properly ventilated when using an acetone or solvent poultice.
If you are uncertain about this application, let a professional apply the solvent based poultice. Apply an acetone or solvent poultice mixture using similar procedures as described under the General Poultice Method.