If Limestone stains it can be an absolute nightmare to remove, you can scrub for hours and it will not budge. The best thing you can do is avoid stains all together, this may seem obvious however here are a couple of things you may overlook:

- Do not keep flower vases containing water on limestone. Even if it does not spill the moisture on the base of the vase can react with the limestone causing permanent ring-like marks.

- Be extremely careful with any fireplace essentials such as wood or coal as the particles can embed themselves in the surface causing it to look dirty.
 
If the worst should happen and you get a stain for any reason then make sure you act fast. The quicker you react, the more likely you are to remove the stain. In fact it may be a wise idea to have a cupboard with emergency cleaning supplies nearby in case needed. Poultices are the best thing for fresh stains. A safe/inert poultice that does not react with limestone can absorb a large quantity of liquid or stains.

Mix a few pinches of baking powder with some distilled water and use this to wet the poultice. Place the wet poultice over the stain and leave overnight. This should remove most fresh stains.

If you have an old or stubborn stain then you can always try a tougher approach, in hopes of getting it out. Make sure you wear rubber gloves and safety glasses as you will be dealing with chemicals.

For organic and inorganic stains, use a strong hydrogen peroxide solution. This can normally be found at a beauty supplier store. Ask for a “clear developer” in either 30 or 40 volume. For oily stains substitute the hydrogen peroxide for a simple acetone.

Add talcum powder to a bowl and add a small amount of either the hydrogen peroxide or acetone whilst mixing with a metal spoon. Mix this until it forms a tooth paste like substance.

Apply the mixture to the stain so it overlaps the stain by about ½ inch and so that the paste is ¼ inch thick. Cover this with plastic wrap and tape down the wrap at the edges with masking tape.

Let this sit for roughly 24 hours before removing the plastic wrap. Let the mix dry completely without disturbing it. Depending on conditions this could take a few days.

Once dried, remove the mix from the limestone surface using a plastic spatula. Wipe the area down with a cloth and cleaner designed for limestone surfaces.

Your stain should have disappeared. Repeat the entire process for more stubborn stains.