This is the most common misunderstanding in the whole category, and it costs people money in exactly the wrong direction.

A stain is something in the stone

A stain is a substance that has migrated into the pores and is sitting there. Red wine in sandstone, oil in an unsealed limestone.

Because the substance is physically present, staining is in principle a removal problem — poultices exist, and prevention works: a sealer occupies the pores so there is nowhere for the wine to go.

An etch is stone that has gone

Etching is a chemical reaction. Acid meets calcium carbonate, the surface dissolves, and the polished finish becomes a matt patch. Nothing is sitting in the stone; some of the stone is missing.

There is nothing to draw out. The only fix is mechanical — repolishing the surface — which is not a thing you do to a coaster.

Why the sealer does not save you

A sealer is not an acid barrier and is not sold as one. It reduces absorption. Against a gin and tonic sitting on polished marble it does very little, because the acid attacks the surface rather than travelling into it.

Marble suppliers are not being dishonest when they recommend sealing. They are answering the staining question. It is just not the question most coaster buyers are asking.

What to do instead

Match the stone to the drink. Granite is unaffected by citrus. Slate is unaffected by citrus. Both engrave well and both are cheaper than marble.

Keep marble where it is admired rather than used hard — boardrooms, guest rooms, closing gifts, display. It is the best-looking stone in the range and it is fragile in a way that has nothing to do with dropping it.