What to clean it with, and what will damage it.
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Sweep grit off daily, mop with a pH-neutral stone cleaner, and never use vinegar, lemon or an abrasive powder. Grit under a shoe is what scratches a marble floor; acid is what etches it. Those are two different problems and two different habits.
First work out what kind of stain it is, because the treatments are opposites. An organic stain is drawn out with a poultice, a metal stain is a poultice as well, and an etch is not a stain at all and no poultice will touch it.
At 0.3 to 0.4 per cent absorption it stains slowly rather than instantly, and most spills can be blotted off if they are caught. What it does do is etch, and an etch is not a stain — it is a layer of the surface that has to be polished back.
A shallow scratch can usually be buffed out with a polishing compound and a soft cloth, and a deeper one needs diamond abrasives. What cannot be polished out is an etch, because that is the surface gone rather than the surface marked.
With a poultice: a powdered absorbent and 12 per cent hydrogen peroxide, left on for 24 to 48 hours under plastic. Coffee and wine are organic stains, which means they went in and can be drawn out — unlike an etch, which is the surface gone.
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