Etching vs Staining on Marble: How to Tell the Difference

The quick test

A stone restorer quoted by the Natural Stone Institute's Use Natural Stone site puts it simply: if a spot is lighter than the surrounding stone, it's most likely an etch mark, and if it's darker, it's probably a stain.

Why marble etches

Marble is made of calcite (calcium carbonate), and calcite is also the main ingredient in travertine and onyx. Calcite reacts with common acids: an etch is chemical corrosion of the stone's surface layer, which leaves a dull mark. That's why sealer can't help: a sealer slows liquids from soaking in, but the reaction happens on the surface. One restorer quoted by the Natural Stone Institute's Use Natural Stone site says sealer "does nothing to protect etching, no matter how much sealer you use."

Some spills do both. Wine, for example, can etch the surface and, if it's left, stain it too.

Etches show more on polished marble

On a polished finish, an etch mark is often invisible straight on but appears duller and less shiny at an angle. A honed finish often makes etch marks less visible than a polished one.

What to do about an etch

• Don't use a stain remover or add more sealer. Neither affects an etch.
• Light etching on polished stone is usually a job for a professional stone restorer, who can refinish or re-polish the area.
• To prevent it, wipe up acidic spills right away, use coasters and trays, and clean only with pH-neutral products made for stone.

What to do about a stain

Identify what caused it, then use the right poultice. See How to Remove Stains from Marble and Stone Floors.

Does this apply to other stones?

Acids can affect any stone that contains calcite or dolomite: marble, dolomitic marble, limestone, travertine and onyx. The Natural Stone Institute notes that siliceous stones, made mainly of silicate minerals like quartz, generally resist most household acids. If you're not sure what your stone is made of, treat it as acid-sensitive.