Etching

The Natural Stone Institute treats an etch and a stain as two different marks, even when one spill leaves both.

NSI's care page lists etch marks in its guide to stains, "caused by acids left on the surface of the stone", and keeps them apart from staining in two sentences: "Some materials will etch the finish but not leave a stain. Others will both etch and stain." An etch is a change to the finish itself, which is why wiping or rinsing does not bring the finish back. NSI's routing for it is direct: "Contact your stone dealer or call a professional stone restorer for refinishing or repolishing etched areas."

Acid is the headline cause of etching, and it is the reason a calcareous surface like travertine or marble carries its own cleaning rule.

NSI warns that "products containing lemon, vinegar or other acids may dull or etch calcareous stones", the class of calcareous stone built mainly of calcium carbonate. Whether an acid cleaner is ever permitted on outdoor travertine is answered at can travertine be cleaned with acid. Acid is not the only route to a dull finish. In its advice on removing paint, NSI says "Paint strippers can etch the surface of the stone; repolishing may be necessary", and in its advice on soap scum it warns that "Frequent or over-use of an ammonia solution may eventually dull the surface of some stone types." Rust removers carry a wider hazard: many contain trace hydrofluoric acid, which NSI says attacks all stones, granite and quartzite included, not only calcareous ones.

Once a stone has etched, NSI's route is refinishing or repolishing by a stone dealer or a professional stone restorer, not a cleaning. This page covers etching in stone only; how marble and travertine compare for cleaning is answered at marble versus travertine, and the cleaning limits the trade bodies publish for concrete pavers, travertine and marble, and clay brick sit side by side in the paver cleaning page's materials section.

Other words on a stone job describe how the pavers are bedded, sand-set or mortar-set, and where a deck meets the water, the pool coping; none of them changes what an etch is or how it forms.