A stone-safe cleaner is one that sits near pH 7 — roughly 6 to 8 — because the calcium carbonate your basin is made of dissolves faster as pH drops, and not gradually. Work published by the U.S. Geological Survey puts a number on it: "Calculations from a rate equation for calcite dissolution predict an approximate 8-fold difference in the initial calcite dissolution rate over the pH range 5.0 to 4.0" (P. A. Baedecker and M. M. Reddy, Journal of Chemical Education, February 1993, 70(2), 104–108). One pH point is not a small step. That single fact decides almost everything about what belongs under a stone sink and what does not.
We carve marble and travertine basins to order every week, and the aftercare question we get most often is "can I just use what I already have?" Usually the honest answer is no — and the reason is chemistry, not brand loyalty.
What "pH neutral" means on a stone cleaner label
The pH scale is logarithmic: pH 4 carries ten times the hydrogen-ion concentration of pH 5, which is exactly why the dissolution rate jumps the way the USGS figures show.
Cleaners formulated for natural stone generally target pH 7 to 8: neutral enough not to attack the stone, slightly alkaline so surfactants can lift body oils and soap film. There is no legal definition of "pH neutral", so look for a stated pH on the technical data sheet rather than the marketing copy. If a product will not tell you its pH, treat that as an answer.
The Natural Stone Institute's guidance is deliberately plain on the daily routine: "Clean stone surfaces with a neutral cleaner, stone soap, or a mild liquid dishwashing detergent and warm water" (A Guide to the Care & Cleaning of Natural Stone, Natural Stone Institute, 2019).
Why acid damage on stone is etching, not staining
The two problems have opposite fixes. A stain is something absorbed into the stone. Etching is stone that is no longer there — calcium carbonate reacted with acid and left as carbon dioxide and dissolved calcium. Scrubbing does not bring it back; etching is corrected by re-honing.
Calcite, the mineral that makes up marble and travertine, sits at 3 on the Mohs hardness scale — it "can be scratched readily by a knife blade or geologic pick", as the University of Waterloo Earth Sciences Museum describes it. Marble is dense (ASTM C503/C503M-15 caps water absorption at 0.20% by weight) but density is not acid resistance. The same USGS research found that at an average rainfall pH of 4.2, hydrogen ion deposition alone accounted for 17% of the chemical erosion of marble test slabs. Rainwater does that outdoors over years. A lemon wedge left in a basin does a concentrated version of it in minutes.
The pH of what is already in your bathroom
Most etching we see photographed by customers was not caused by a cleaning product at all. It was caused by something ordinary sitting on the stone. Published pH figures, drawn from the FDA's Bacteriological Analytical Manual food pH tables and standard product data:
| Substance | Typical pH | Effect on calcareous stone |
|---|---|---|
| Lemon juice | 2.00 – 2.60 | Etches on contact |
| Lime juice | 2.00 – 2.35 | Etches on contact |
| Vinegar (distilled) | 2.40 – 3.40 | Etches on contact |
| Many limescale / bathroom descalers | 1 – 3 | Severe etching |
| Dedicated stone cleaner | 7 – 8 | Safe for daily use |
| Household ammonia solution | 11 – 12 | Dulls finish with repeated use |
| Sodium hypochlorite bleach | 11 – 13 | Attacks sealer, may discolour |
The safe band is narrow, and the common products sit well outside it in both directions.
The acidic end: the four to remove from the cabinet
The Natural Stone Institute is unambiguous about the household favourites: "Products containing lemon, vinegar or other acids may dull or etch calcareous stones." In practice, the four worth physically removing from a bathroom with a stone basin are:
- Vinegar sprays, including home-made "natural" ones. Acetic acid at pH 2.4 does the same thing whether it came from a supermarket or a recipe blog.
- Limescale and hard-water removers. These work precisely by dissolving carbonate deposits. Your basin is carbonate. The product cannot tell the difference.
- Toilet bowl cleaners — often strongly acidic, and frequently set down on stone mid-clean.
- Rust removers. NSI warns that many "contain trace levels of hydrofluoric acid (HF). This acid attacks silicates in addition to other minerals."
Beyond cleaners: citrus, wine, cola, and exfoliating products with glycolic or salicylic acid. In a powder room that exposure is occasional; in a primary bathroom basin it is daily.
The alkaline end nobody warns you about
Acid gets the attention, but strong alkalis cause a slower problem. Bleach and ammonia at pH 11–13 degrade impregnating sealers — typically silane or siloxane based — well before they visibly harm the stone. The basin then behaves as if it were never sealed, and the owner concludes the stone is "too porous" when the sealer was stripped.
NSI notes that "frequent or over-use of an ammonia solution may eventually dull the surface of some stone types", and adds a safety line worth repeating: "Do not mix ammonia and bleach. This combination creates a toxic and lethal gas."
The same institute is careful about what sealing does at all: "Sealing does not make the stone stain proof: rather, it makes the stone more stain resistant." A sealer buys you time to wipe a spill. It does not create an acid barrier — an impregnating sealer sits below the surface and does nothing to stop etching.
What we actually recommend
Our aftercare instruction fits on one card, and it is the same for a Carrara basin and a travertine one:
- Daily: rinse with warm water, dry with a soft cloth. Most bathroom marks are water spots and soap film, and drying prevents both.
- Weekly: pH-neutral stone cleaner, or a few drops of mild washing-up liquid in warm water. Rinse fully — residue creates the dull film people mistake for damage.
- Never: vinegar, citrus, descalers, bleach, scouring cream. NSI notes that "scouring powders or creams often contain abrasives that may scratch certain stones", and at Mohs 3 that is easy to do.
- Re-seal when water stops beading and starts darkening the surface — typically annually, depending on stone and sealer.
Choosing between the two stones changes aftercare less than people expect — both are calcium carbonate, so both want the same neutral pH. What differs is surface structure, covered in the marble sink guide and the stone sink guide. If you want the finish chosen around real-world use rather than a showroom photograph, send your dimensions through custom order for a fixed quote and a technical drawing before anything is cut.
Frequently asked questions
What pH should a stone cleaner be?
Between roughly 6 and 8, with 7 to 8 typical for products formulated for natural stone. The reason is that calcite dissolution accelerates sharply as pH falls — USGS research predicts an approximate 8-fold increase in the initial dissolution rate between pH 5.0 and pH 4.0. Above pH 10, strong alkalis degrade impregnating sealers instead.
Can I use vinegar to clean a marble sink?
No. Distilled vinegar measures pH 2.40 to 3.40, and the Natural Stone Institute states that "products containing lemon, vinegar or other acids may dull or etch calcareous stones." The damage is etching — dissolved stone — which cannot be wiped away and has to be re-honed out.
Is dish soap safe on a stone basin?
Yes, for a mild liquid washing-up detergent diluted in warm water. It is one of the three options the Natural Stone Institute lists for routine cleaning. Rinse thoroughly, because detergent residue builds a dull film that is often mistaken for damage to the stone.
Does sealing protect a stone sink from acid?
No. An impregnating sealer reduces absorption and buys time to wipe a spill, but it does not prevent etching, because the acid reacts with calcium carbonate at the surface. As the Natural Stone Institute puts it, "sealing does not make the stone stain proof: rather, it makes the stone more stain resistant."
