925 sterling silver: everything you should know

Silver is the most misunderstood metal in jewellery, mostly because the honest answers are slightly inconvenient for people selling it. Here are the honest answers.

What 925 means

92.5 per cent pure silver, 7.5 per cent other metals, almost always copper. That is the whole definition. The number is a millesimal fineness standard, not a brand or a grade of quality.

Pure silver, at 99.9 per cent, is too soft for jewellery. It bends under ordinary handling and it will not hold a stone: a prong made of fine silver would open on its own. The 7.5 per cent copper is what gives sterling the stiffness a setting needs.

So when a site says "925 sterling silver" it is telling you the alloy is correct. It is not telling you the piece is well made. Those are separate questions.

Why it tarnishes, and why that is not a fault

Tarnish is a chemical reaction. The copper in the alloy reacts with sulphur compounds in the air and forms silver sulphide on the surface, which is the dark film you see. It is not rust, it is not dirt, and it is not corrosion eating the metal. It is a surface layer a few molecules thick.

Things that speed it up:

Humidity, which is why silver tarnishes faster during a monsoon
Sulphur in the air, including from pollution
Perfume, hairspray, sunscreen and chlorinated water
Some cosmetics, and the natural chemistry of your own skin, which varies

Things that slow it down:

Wearing it. Skin contact keeps silver bright. Jewellery kept in a drawer tarnishes faster than jewellery worn daily. This surprises people.
Storing it dry, in a closed pouch, away from air
Rhodium plating, which is the next section

What rhodium plating does

Rhodium is a platinum-group metal. Plated in a very thin layer over sterling silver, it does three things: it is harder, so the surface resists scratching; it does not react with sulphur, so tarnish slows dramatically; and it is slightly whiter and cooler than raw silver, which suits pale blue and grey stones better.

The honest limitation: rhodium plating wears. On a ring worn every day, expect the high points to begin showing warmer silver underneath after somewhere between one and three years, depending entirely on how you use your hands. Earrings and pendants can go a decade. Replating is a routine, inexpensive job at any competent jeweller.

Anybody who tells you a plated finish is permanent is either not paying attention or hoping you are not.

How to clean it, in about a minute

For light tarnish, which is the overwhelming majority of cases:

Warm water, a drop of mild washing-up liquid
Soft toothbrush around the setting, gently
Rinse, then dry completely with a soft cloth
Finish with a silver polishing cloth, the impregnated kind

That is it. What you should not do:

No ultrasonic cleaner. Fine for a plain band. Potentially destructive for moonstone, labradorite, lapis or any stone with internal fractures.
No steam cleaner, for the same reason.
No dip-style chemical tarnish removers on anything with a stone or a plated finish. They strip rhodium and can attack porous stones.
No toothpaste. It is an abrasive, and it will scratch a polished surface and dull a rhodium finish. This piece of internet advice will not go away and it remains wrong.

For lapis specifically, at 5 to 6 on the Mohs scale and porous: do not soak it at all. A barely damp cloth, and dry it immediately.

How to tell real sterling from plated

Four checks, in order of reliability:

The stamp. Genuine sterling is stamped 925, sometimes "STER" or "STG", usually inside a band or on the back of a setting. Absence of a stamp is not proof of anything, because very small pieces are hard to stamp, but its presence is meaningful.

Hallmarking. In India, BIS hallmarking for silver is a voluntary certification scheme that confirms fineness independently. Where a piece is hallmarked, that is a genuinely verifiable signal rather than a claim.

The magnet test. Silver is not magnetic. If a piece is attracted to a magnet, the core is a ferrous metal and it is plated. This test only catches the worst offenders.

Tarnish pattern. Sterling tarnishes evenly across the whole surface. Plated base metal tends to wear through at edges and high points and expose a different colour underneath. If you see two colours, it is plated.

What to realistically expect

If you buy sterling silver jewellery intending to wear it for years, here is the truthful version:

It will be bright for a long time if you wear it often
It will darken if you leave it in a box for six months, and a cloth will fix that in a minute
The plating on a daily-wear ring will eventually wear at the high points, and replating is straightforward
It will scratch. So does platinum. So does gold. A piece of jewellery worn for a decade should look like it has been worn for a decade.

That last point is the one worth sitting with. A stone can be kept perfect. A metal that touches your skin every day cannot, and should not have to be.

Read the full care guide for storage and per-stone specifics, or the stone guide for how each material behaves.