Here’s a step by step guide to make a “poultice” for removing oily stains (any type of vegetable oil, mineral oil, butter, animal fat, etc):
1. Get acetone (from hardware store, not nail polish), and very absorbent, good quality paper towels.
2. Make a paper towel cushion (8-10 folds, or a 1/4 inch thick) which is a little wider than the stain.
3. Soak the paper towels with the acetone to a point that it is wet through, but not dripping.
4. Apply it on the stain and tap it with your gloved fingertips to insure full contact with the surface of the stone.
5. Cover your “poultice” with plastic wrap, then tape it down using masking tape.
6. Leave the poultice alone for at least 24 hours, and then remove the plastic wrap, but not the poultice yet.
7. Allow the poultice to dry thoroughly. It may take a few hours or a few days or more, depending. Resist the urge to lift it prematurely… let it completely dry. This is the phase during which the absorbing agent is reabsorbing the acetone that was forced into the stone, together with the oily stain.
8. Once the poultice is completely dry, scrape it off with a plastic spatula, clean the area with a spray cleaner rated for natural stone or water, and wipe clean.
If some of the stain is still there, repeat the procedure (with some oily stains, it may take up to 4 or 5 attempts). Remember, this procedure is for oily stains only.
For organic & inorganic stains (coffee, tea, sodas, gravy, mustard, color dies, etc) Hydrogen Peroxide 30/40 volumes (approx 11-14%) is used instead of acetone. Hydrogen Peroxide from the drug store is too weak; usually you can find this strength at a supply store but you should have a pro use these products.