Stainless steel pan
Stainless is not stain-proof, and both of its common blemishes — rainbow tinting and white pitting — are chemistry rather than dirt.
Start here
What this is, what tends to go wrong with it, and what to do about it.
Made from
What tends to go wrong
Food heated until it carbonised and bonded to the surface. Time and softening do the work; scouring powder does the damage.
Why it is difficult: Contact time, Carbonisation, Adhesion and cohesion, Why old stains are harder
The rainbow or brown bloom on stainless steel that has been heated. Not a deposit and not dirt: the metal's own surface oxide, thickened by heat.
A hard, chalky calcium carbonate deposit left by hard water. Dissolved by acids, essentially untouched by detergents.
Why it is difficult: Water hardness, Crystallisation, Adhesion and cohesion
Hydrated iron oxide from corroding iron or steel. Distinguish a surface deposit, which cleans off, from active corrosion of the item itself, which does not.
Why it is difficult: Corrosion and passivation, Why old stains are harder, Adhesion and cohesion
- Fingerprintsvia its material
Skin oils transferred by touch. A greasy soil rather than a dirty one, which is why water alone does not shift them and why they return immediately.
Why it is difficult: Surfactancy
- Water marksvia its material
What hard water leaves behind when it evaporates instead of being wiped away. A mineral film, not dirt, and the fix is at the drying stage.
Why it is difficult: Water hardness, Evaporative deposition
- Greasevia its material
Fats and oils, which water alone cannot lift. Removed by surfactants, by heat, by solvents, or by alkalis that convert the fat into soap.
Why it is difficult: Why oil resists water, Emulsification
The science behind this: Corrosion and passivation, Water hardness, Chloride attack, Cleanability is designed in
In detail
Stainless steel resists corrosion because chromium in the alloy forms a thin, self-repairing passive oxide film on the surface. Cleaning it well means keeping that film intact, and the two marks people most often try to scrub off are not soil at all. Rainbow or straw-coloured tinting inside a pan is heat tint — interference colours from an oxide layer thickened by heating — and it is a cosmetic change rather than corrosion. White pitting or spotting is usually chloride attack, from salt added during cooking or from food residue left standing, and chlorides are the one thing that reliably breaks the passive layer. The steel trade's guidance follows from that: clean with a mild detergent or a proprietary stainless cleaner, work in the direction of the finish where the surface is brushed, rinse and dry, and use non-metallic pads where mild abrasion is needed. What it excludes matters more. Carbon-steel implements and steel wool leave iron particles that corrode and appear as rust staining on the surface, which is the usual explanation for a stainless sink that has apparently started rusting. Bleach and chloride-containing cleaners should not be left in contact.
Related
- Stainless steel pan is made from Stainless steel
- Stainless steel pan is commonly affected by Burnt-on food and carbon deposits
- Stainless steel pan is commonly affected by Heat tint
- Stainless steel pan is commonly affected by Limescale
- Stainless steel pan is commonly affected by Rust
Sources for this page
Sources
Care and Maintenance of Stainless Steel
British Stainless Steel Association, Stainless Steel Advisory Service, 2001 · Trade or professional body
Relied on for: That chromium forms a passive layer, that chlorides attack it and cause pitting, and that carbon-steel implements and steel wool leave iron particles which corrode and appear as rust staining. (states this directly)
Cleaning methods for stainless steel
British Stainless Steel Association · Trade or professional body
Relied on for: That cleaning follows the direction of the finish, that non-metallic pads are used where mild abrasion is needed, and that rinsing and drying are part of the method. (states this directly)