Can mineral deposits be polished off glass?

Read against NGA's cleaning paper and the PGT, CGI and WinDoor care guide, the finding is empty: neither says mineral deposits can be polished off a pane.

NGA does name mechanical polishing, alongside razor blades and chemical cleaning, in one sentence set out in full below, and that sentence carries a construction condition. NGA's list of conditions that may call for aggressive techniques names construction soils such as paint overspray and mortar, not mineral deposits, and because NGA says the list is not limited, that absence proves nothing in either direction.

The sentence reads differently in full than in half.

NGA's section, headed Non-Routine Post-Construction Cleaning & Restoration, says glass "that is improperly stored or left unprotected during construction may result in glass that cannot be successfully cleaned using routine cleaning procedures," and that in such situations more aggressive cleaning and restoration techniques, razor blades, chemical cleaning or mechanical polishing among them, may become necessary. That condition, glass mishandled during construction, is doing real work in the sentence: it is the situation NGA is describing, not a general rule for any pane with a stubborn spot. NGA attaches a warning to every non-routine technique, that irreparable damage to the glass is possible, and where routine cleaning stops, with that condition kept, is set out on how exterior glass gets cleaned.

A separate document, the window makers' care guide, lists what may not be used on their products.

Among the items the PGT, CGI and WinDoor precautions list says not to use on their windows, screens, doors or hardware are razor blades and abrasive pads, abrasive or caustic cleaners, and hydrochloric or phosphoric acid. NGA's own list keeps acids, especially muriatic or hydrochloric and hydrofluoric, out of glass cleaning solutions entirely and says razor blades should never touch a coated glass surface. Neither document recommends a product or a technique for a mineral deposit.

It is worth naming what routine cleaning actually is, since polishing is not it.

NGA's published method soaks the glass with clean water and a mild, non-abrasive cleaning solution, then removes all of it with a squeegee immediately after application, and its glass cleaning solutions exclude acids outright. That is the routine NGA publishes for the soil routine cleaning is written to handle. Polishing sits instead under NGA's heading for non-routine cleaning and restoration, a distinction can windows be too dirty to clean covers from the other direction.

The words behind the term come from water heaters, dishwashers and plumbing, not from windows.

USGS calls the spots or film on glasses taken out of a dishwasher hard-water residue, and says solid deposits of calcium carbonate can form when hard water is heated, such as in a home water heater. EPA's secondary standards describe scale as a mineral deposit that builds up on the insides of hot water pipes, boilers and heat exchangers. Neither says when a deposit on window glass becomes permanent, or whether it does, and no source read for this page does either; the term itself is defined at mineral deposit.

Nothing above settles the question for one specific pane, and that gap is the honest answer rather than a missing one.

Because of that risk of irreparable damage, NGA wants the responsible parties to talk it through before anyone reaches for an aggressive technique. Whether a spot on a given window is a deposit that will respond to anything at all, and what a glass restoration professional or the glass maker would try, is a judgment made on that pane, not from a description of it. A related question with its own answer is why spots survive regular window cleaning in the first place, and whether a razor blade is ever appropriate is answered separately as well.