Stainless steel was an accidental invention. In 1913, an English metallurgist named Harry Brearley was testing various alloys for use in gun barrels. He wanted an alloy that was hard, so he tested different combinations — nickel one day, chromium the next, aluminium after that.

About a month later, while walking through his lab, he noticed a gleaming bit of metal in the pile of rusted bits. He referred to his notes and realised that it was likely a new form of steel. For the bit in question, he’d taken the two elements that make up steel (iron and carbon) and added chromium.

Brearley was intrigued. Why would this piece alone not rust? It turned out that this was because the chromium acted like a force field, reacting with oxygen to form chromium oxide. The chromium oxide created a hard, transparent coating on the metal, a barrier against future oxidisation. If the surface was scratched, the chromium just re-formed the barrier, preventing rust in perpetuity.

Brearley called his new alloy “rustless steel”. As it happened, his hometown of Sheffield was a hub of cutlery-making at the time. A former schoolmate named Ernest Stuart was among the local cutlery makers. Brearley showed him the rustless steel, and it was Stuart that suggested the better-sounding name “stainless steel”.

Soon Brearley’s invention was in everything. In the kitchen, stainless steel knives meant one no longer needed a tetanus shot after an accidental cut. Over time, spoons became stainless steel by default; only people above a certain age will remember the metallic tang of the mixed-metal spoons that came before.

Razor blades, surgical blades, teeth braces all switched too; no rust meant the user was safe even if they got knicked or scratched. Sinks, kitchen appliances, pipes, even space rockets have taken to this metal, and new uses continue to be found.

In order to remain stainless, steel must be at least 10.5% chromium. Most high-quality food-grade stainless steel pans are specified as 18/8 or 18/10. These numbers reflect the levels of chromium and nickel respectively, in the alloy; higher numbers indicating improved corrosion resistance.

Low-cost stainless steel may skip the nickel, but the resultant alloy is more likely to corrode over time, especially if it comes in frequent contact with corrosive acids or salts.

Some people prefer nickel-free stainless steel for kitchen implements, because there have been concerns in recent years that the nickel could leach into the food. Manufacturers have responded by offering stainless steel with the specification 21/0, commercially called Japanese stainless steel. But the truth is that people get a lot more nickel from foods such as peanuts, peas and milk chocolate than from cooking in a stainless steel pan, and all of these foods are of course safe to consume. On average, in fact, a person ingests about 150 to 200 microgrammes of nickel a day, through food.

Read: How to pick a good stainless steel pan: Tips from Swetha Sivakumar

If you have been diagnosed with a nickel allergy, however, it is best to avoid regular stainless steel. For the rest, perhaps the best thing about stainless steel is that it needs little to no care. It has none of the high levels of acidic leaching of aluminium pots; requires none of the conditioning of cast iron; none of the delicacy needed with Teflon.

You may sometimes see a rainbow stain on a stainless steel pan. This is harmless and the result of too much chromium oxide deposited over time. It can be erased by rinsing the pan with a light acid such as lemon juice or diluted vinegar. If using hard water, look out for a powdery deposit from the calcium in it. Like the rainbow stain, it may be resistant to soap but will dissolve in the presence of acid. A simple rinse and it can go back on the shelf or in the drawer, with a little thank-you to the deity of happy accidents.

(To reach Swetha Sivakumar with questions or feedback, email [email protected])

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