Cleaning metals
Five metals that fail in five different ways: passive layers, amphoteric attack, plating thinner than a hair, and tarnish that is the metal itself.
What this area turns on
Sprint 23 added the metal whose normal maintenance CONSUMES it, and it reframes the whole guide. Tarnish is silver sulphide - a compound containing silver - so every clean removes a little of the object, and both conservation bodies read for this catalogue say so plainly. That makes the professional answer restraint rather than technique: keep tarnish removal to a minimum and use the mildest non-abrasive method. Polishing creams, wadding and rouge sticks are the damage rather than the treatment, carrying corrosive acids as well as abrasives. On PLATE the arithmetic changes completely: the silver is microns thick, and over-polishing removes it entirely, exposing dull base metal that CAN BE MISTAKEN FOR TARNISH - which invites more polishing of the one spot with nothing left. And the foil-and-bicarbonate hack, whose chemistry genuinely works, belongs to the electrochemical class both bodies rule out. Almost every metal problem in a house is a surface that is a few microns thick behaving differently from the metal beneath it. Stainless steel depends on a passive oxide film that chloride breaks down; aluminium is amphoteric and dissolved by strong alkali, releasing flammable hydrogen as it goes; a modern tap is a coating measured in microns, so a polish that removes material removes finish; and on copper the tarnish is not a deposit at all but the metal in a reacted state, so every polish is subtractive.
Where the obvious answer is wrong
Cases where the treatment that removes the problem is the treatment that ruins the surface it is on.
Can I use oven cleaner or a strong degreaser on aluminium?
Aluminium is amphoteric — attacked by strong bases as well as by strong acids. The alkali dissolves the protective oxide film and then the metal beneath, leaving a dull grey or blackened surface that is not a deposit and cannot be cleaned off. There is a second consequence that is a safety matter rather than a cosmetic one: a US state hazardous substance fact sheet records that sodium hydroxide reacts with metals including aluminium to form flammable and explosive hydrogen gas, which is not what anybody expects from cleaning an oven tray in a confined space.
How do I get rid of rust that keeps coming back on a chrome fitting?
Where the plating has been breached, the rust is not sitting on the surface — it is the steel underneath corroding and showing through. Removing what is visible does nothing to the corrosion producing it, and the treatments make the situation worse in two ways: an acid or chelant reaching bare substrate through a breach attacks it directly, and abrasion widens the breach that let moisture in. The mark returns, faster each time.
Can I use a limescale remover on my bathroom taps?
The visible part of a modern tap is a plated, physical-vapour-deposited or powder-coated finish a few microns thick, not solid metal. The manufacturer's care sheet states that PVD finishes must not meet cleaners containing ammonia, bleach or acid, which excludes most limescale removers and a good share of bathroom sprays. Because the finish is microns thick there is no margin: material lost is coating lost, the dulling is progressive, and it cannot be polished back because there is nothing underneath to polish.
Can I leave a cast iron pan to soak to get the burnt-on food off?
Cast iron is bare iron protected by a layer of polymerised oil, and that protection is defeated by water rather than by scrubbing. The manufacturer's wording is blunt: SOAKING CAST IRON IN WATER IS A RECIPE FOR RUST. It extends the same warning to cookware left in the sink to soak, put in the dishwasher, allowed to air dry, or left in a moisture-prone environment — and states that a dishwasher will remove the seasoning and likely cause rust. The failure is not the burnt food coming off. It is that the pan is left in prolonged contact with the one thing its finish exists to keep off it.
How do I get tarnish off silver-plated cutlery without wearing the plating through?
That sentence is also the problem. Tarnish CONTAINS silver, so removing it always removes a little metal, and abrasive polishes carry corrosive acids as well as abrasive compounds. On solid silver that is a slow recurring cost. On plate the silver is only microns thick, so the same treatment is a countdown - and the museum sheet records how it ends: over-polishing plated silver removes the plating and exposes dull base metal that CAN BE MISTAKEN FOR TARNISH. The reader then polishes harder, on the one area with nothing left.
Assessed and found wanting
Widely repeated techniques in this area that the evidence does not support, or supports only in part.
Steel wool for stubborn marks on stainless steel
Does not workIt works in the moment and creates the next problem. The embedded carbon steel particles it leaves behind are what later look like the stainless steel rusting.
Leaving bleach in the sink overnight
Does not workNamed and advised against by the stainless steel trade association, and it is also how two of the documented chlorine gas exposures began.
Never use soap on cast iron
Does not workAmong the most confidently held rules in domestic cooking, and the manufacturer contradicts it outright. The prohibition outlived the soap it was formed around.
Oven cleaner for a stubborn worktop mark
Does not workReaching for the strongest thing in the cupboard when a mark will not shift. On engineered quartz the manufacturer prohibits it outright.
Right about the bath, the taps and the mirror. Wrong about the toilet and basin, where the manufacturer permits a soft abrasive outright.
Toothpaste as a metal polish
Does not workA mild abrasive in a tube, and the tap manufacturer names it specifically among the things that must not be left on the finish.
Tarnish is the metal, not dirt on it. The conservation procedure's position is that copper alloys should usually not be polished at all.
Using oven cleaner in a self-cleaning oven
Does not workThe manufacturer prohibits it outright, and gives a mechanism nobody expects: the residue is what damages the oven, and it does so on the next self-clean cycle.
Decanting bleach into another container
Does not workThe regulator's sheet is about containment rather than surfaces, and it is specific: bleach should not be handled in equipment containing common metals, because the reaction can rupture the container.
Its health rating is 1 and its flammability rating is 3. The hazard people underrate is the one the regulator rates highest.
Lining hob drip pans with foil
Does not workSaves cleaning, and the manufacturer forbids it with three consequences named: shock, fire or damage to the range.
Orange sunscreen marks are rust
Does not workThey contain iron and they are the colour of rust, and they are not rust. The iron comes from your water and the sunscreen grabs it — which changes what removes them.
The chemistry is real and it is the reason to be careful. Both conservation bodies read here rule out electrochemical cleaners, and on silver PLATE the stakes are highest.
The records
Sterling silver
Material or surface92.5% silver, and the only material here where the standard domestic treatment permanently removes some of the object. Tarnish contains silver, so cleaning it off costs silver.
Silver plate
Material or surfaceA microns-thin layer of silver over a base metal. Everything that cleans sterling also thins the plating, and once it is through there is nothing underneath to polish.
Polishing removes metal
ScienceEvery polish takes a little of the object away. On solid metal that is a slow cost; on a plated one it is a countdown, and the end of it looks like more tarnish.
Tarnish
Stain or problemThe only contaminant in this catalogue that is made of the surface it is on. Removing it always removes metal.
Stainless steel
Material or surfaceSteel protected by a self-repairing chromium oxide layer. Resistant to most household cleaning, and specifically vulnerable to chlorides and to abrasion across the grain.
Aluminium
Material or surfaceProtected by its own oxide layer, but amphoteric: attacked by strong alkalis as well as strong acids, which rules out many oven and dishwasher products.
Chrome plating
Material or surfaceA thin decorative chromium layer over another metal. Hard and bright, but once the plating is breached the metal underneath corrodes and no cleaning reverses it.
Copper and brass
Material or surfaceTarnish is the metal reacting with its surroundings, not dirt on top of it. Every polish that removes it removes metal too.
Plated and coated tap finishes
Material or surfaceModern taps are a coating on a metal, microns thick. The finish decides the rules, and the rules genuinely differ between finishes on the same basin.
Seasoned cast iron
Material or surfaceBare iron protected by a baked-on oil layer. Water is the enemy, not detergent — and the manufacturer says so more plainly than the folklore does.
Rust
Stain or problemHydrated iron oxide from corroding iron or steel. Distinguish a surface deposit, which cleans off, from active corrosion of the item itself, which does not.
Corrosion and passivation
ScienceMost corrosion-resistant metals are protected by an invisible oxide film. Cleaning either preserves that film or breaks it, and breaking it is how stainless steel rusts.
Cleaning along the grain
MethodOn a brushed or directional finish, the direction you wipe decides whether marks disappear into the pattern or cut across it permanently.