Etching: what it is, what causes it, and how it comes out.

Marble, limestone and travertine are calcium carbonate. When an acid meets them it dissolves a microscopic layer of the surface, and the polished face that used to reflect light now scatters it. That roughened patch is an etch. It feels smooth, it looks dull, and it is a change to the stone, not something sitting on it.

What causes it

In a kitchen: lemon and lime, vinegar and dressings, wine, tomato, soft drink, coffee, fruit. A wet glass of anything citrus leaves a ring by condensation alone. In a bathroom: most sprays, descalers, toilet cleaners, rust removers, some exfoliants and hair products, toothpaste. From the cleaning cupboard: nearly everything labelled for kitchens, bathrooms, limescale or grout, and most "natural" cleaners, because they are vinegar or citrus. Severity depends on the acid, how long it sat and how many times.

Why it is not a stain

A stain is colour that has gone into the pores: darker than the stone. An etch is lighter, duller, sometimes slightly rough, and it looks the same wet or dry. Red wine does both at once, pigment in the pores and acid on the face, and each half is treated separately. The distinction decides everything, because a poultice does nothing for an etch and honing does nothing for a stain.

Why sealing does not prevent it

A sealer lines the pores below the surface. The acid reacts with the surface. A bench sealed last week etches under lemon juice exactly as an unsealed one does. Sealing is for stains.

Where it shows most

On polished stone, because the contrast between reflection and dullness is greatest; on dark marble, where an etch reads as a chalky patch; near bar areas, buffets and bathrooms in commercial spaces where spills and aggressive cleaning meet. Honed stone hides light etching, which is one reason busy kitchens are honed, but it etches just the same.

What a home attempt can do

A very light etch on a small, non-critical area may respond to a polishing powder made for calcite stone, used exactly as directed on a clean dry surface and stopped after one measured go. The risk is control: too wide, too hard, or the wrong grit and you get a halo, a glossier patch on a honed top, or a dull one on a polished top, and it is more visible than the etch. Vinegar to "cut" it, baking soda paste, cream cleanser, a magic eraser and generic stone repair products all make it worse. On limestone the same applies with less margin, because the stone is softer and the honed finish is easy to accidentally gloss.

How it is removed

The surface is cleaned so the true extent shows, then honed with fine diamond abrasives to take the altered layer off evenly, then polished back to the finish it had, or left honed if that was its finish. On a benchtop that is usually a couple of hours on the bench with the kitchen protected. On a floor, scattered etches across a polished surface are not spot-treated; the room or a defined section is honed as one surface so the finish is even tile to tile. Deep etching that has left a visible dip takes more honing and blends less perfectly, and that is the case where a test patch is cut first and shown to you.

Prevention

Wipe acidic spills when they happen, blotting rather than scrubbing. Trays under bottles, oils, soaps and cosmetics. Coasters under drinks. Boards for cutting. A neutral stone cleaner and nothing else. In a building, the cleaning contract names the products, because a general bathroom spray used nightly is how a marble foyer goes dull in a season.