925 sterling silver — composition, hallmarks, and how it differs from other silver standards

By Dmitry Strugovshchikov, founder of STRUGA

The number 925 stamped on silver says one thing: of every thousand parts of the alloy, at least 925 are pure silver, and the other 75 are alloy metal — almost always copper. That alloy is sterling silver. A stamp describes the metal; it says nothing about who made the piece, or how.

925 sterling silver is at least 92.5% silver, the rest usually copper; «925», «.925», «S925», «Ag 925» and «sterling» all mark one standard.

In the US, an article stamped «sterling» may fall short of 925 by no more than 4 parts per thousand (15 U.S.C. § 296).

Sterling tarnishes faster than fine silver because of the copper: the dark film is silver sulphide, a property of the metal, not a defect.

A UK hallmark has three compulsory marks — sponsor, fineness and assay office; silver under 7.78 g is exempt.

STRUGA silver is uncoated 925; a size-17 Brutalism V.1 ring carries 10.6 g of pure silver.

Updated September 29, 2026

The number is easiest to read on a real object: a size-17 Brutalism V.1 Ring weighs 11.5 g, and 10.6 g of that is pure silver. The table for other pieces is in the STRUGA section below.

What does 925 sterling silver mean?

925 means the alloy contains at least 925 parts of silver per thousand by weight — 92.5%. The number is a floor, not an average: fineness is expressed in parts per thousand, and a sterling piece must reach it. The remaining 75 parts are alloy metal added for strength, traditionally copper.

In the United States the word «sterling» is regulated. Under the FTC Jewelry Guides (16 CFR 23.5), «sterling», «sterling silver» and «solid silver» may only describe metal of at least 925 fineness, and «coin silver» at least 900. The federal stamping law allows an article marked sterling to fall short by no more than 4 parts per thousand, or 10 when the whole article, solder included, is assayed.

925 is also one of only three silver fineness standards recognised by the 1972 Vienna Convention on hallmarks, alongside 999 and 800. The alloy is the same everywhere: 925 in Italy, in the UK and in Indonesia is the same metal.

Is 925 real silver or a different metal?

It is silver. Not a separate metal, not white gold and not a silver-coloured substitute. Silver sets the colour of the alloy — a cool silvery white — and 7.5% of copper does not visibly shift it, so to the eye sterling reads as fine silver.

Nickel silver and German silver are a different story. They are copper-nickel-zinc alloys with no silver in them at all; the name describes the colour, not the content. Pieces sold as «925» that turn out to be these alloys are the reason a check starts with the marks and the magnet and ends with a jeweller.

Sterling should not look yellow. A light piece stamped 925 that leans towards yellow is most likely gold-plated. Dark grey and graphite tones are something else: tarnish, a sulphide film on the surface.

What do S925, Ag 925 and «925 platinum» mean?

S925 and Ag 925 are the same 925 standard written differently. «S925» stands for silver 925 and is common on pieces from Asian factories and marketplace sellers; «Ag 925» uses the chemical symbol for silver. «.925», «925/1000», «STER» and «Sterling» are the English forms. The letters change nothing about the metal.

«925 platinum» is not platinum. It describes sterling silver with a thin surface layer, and under the FTC Guides calling a surface-coated product «platinum» without qualification is deceptive; a rhodium layer on a precious-metal product must be disclosed. The same caution applies to every stamp above: it is the seller's statement about the metal, not a test. How official marks work country by country is covered in our guide to 925, 950 and 999 hallmarks.

What is in the 7.5% of a 925 alloy?

Traditionally, copper. Russia's jewellery alloy standard GOST 30649-99, for example, defines its 925 grade as 92.5–93.0% silver with the rest copper and caps lead, iron, antimony and bismuth at thousandths of a percent. Copper is there for strength: it makes the alloy one and a half to two times harder than fine silver while barely touching the colour.

Copper also has a cost — it is why sterling darkens faster than fine silver. Some alloys replace part of it. The most widely used of them is Argentium, developed by silversmith Peter Johns at Middlesex University in London: germanium takes the place of some copper, and the alloy resists tarnish noticeably longer. It is made in 940 and 960 fineness, so it is a different alloy from classic sterling rather than a variant of it.

How skin reacts to jewelry, and why, is covered in our hypoallergenic silver jewelry guide.

What are the density and melting point of 925 silver?

Sterling has a density of about 10.36 g/cm³, slightly lower than fine silver because copper is lighter. It does not melt at a single point but across a range — 779 to 896 °C according to GOST 30649-99 — while fine silver melts at 961.8 °C. The main properties side by side:

Property	925 sterling	999 fine silver
Silver content	92.5–93.0%	at least 99.9%
The rest	copper	trace impurities
Density	10.36 g/cm³	10.49 g/cm³
Hardness	77 HV soft, 170 HV work-hardened	50 HV soft, 80 HV work-hardened
Melting	779–896 °C	961.8 °C
Magnet	no attraction	no attraction

Density doubles as a check at home: a solid piece weighed in air and then in water gives about 10.4 for sterling and about 8.7 for nickel silver.

What does a 925 hallmark look like?

A full UK hallmark has three compulsory marks: the sponsor's mark (who stands behind the piece), the fineness mark — the number 925, often with the traditional lion passant — and the mark of the assay office that tested it, such as London's leopard's head. Silver articles under 7.78 g are exempt, so a light chain or a pair of studs can legally carry no hallmark at all, according to UK government guidance.

Outside the UK the picture varies. In the US, «925» or «sterling» is the maker's claim with no state assay behind it, backed by the federal law above; other countries run assay offices of their own. The mark sits on a hidden part of the piece: inside a ring shank, on a chain clasp, on an earring post.

The reading order is the same everywhere: fineness first, then the maker's or sponsor's mark, then an assay mark where the country uses one. A bare number with no maker's mark next to it is a reason to ask the seller a question.

How is 925 different from 800, 900, 958 and 999 silver?

The difference is how much copper is in the alloy, and that sets hardness, tone and the pace of tarnish. Which grade goes where is trade tradition rather than law.

Grade	Silver	Where you meet it	What the alloy gives
800	80.0%	older German and Italian tableware	hard, tarnishes fastest
900	90.0%	«coin silver» in the US	more copper, tarnishes faster than sterling
925	92.5%	rings, chains, bracelets, earrings	balance of hardness and colour
958	95.8%	UK Britannia standard	softer, used for plate
999	99.9%	bullion, coins, electronics	soft, will not hold shape in wear

999 is the bullion grade: under the rules of the London Bullion Market Association, a silver bar must be at least 999 parts per thousand. Britannia, 958, is an older English standard introduced in 1697 and still legal alongside sterling. A closer comparison of the three grades most buyers weigh up is in «875, 925 or 999 silver — which is best».

Why did 925 become the jewelry standard?

Because fine silver is too soft for a ring. GOST 30649-99 lists pure silver at 50 HV annealed and 80 HV work-hardened; the 925 alloy at 77 and 170. That gap is the difference between a thin band that bends out of round and one that holds its shape for decades. Rings, chains and bracelets are made in 925; bars are made in 999.

The price of that strength is tarnish. Copper speeds up the reaction with sulphur, so sterling darkens faster than fine silver. Anyone who wants metal that never changes should not choose uncoated silver. Anyone who likes darkening as a record of wear should choose exactly that.

The weight is where the alloy shows. The Thorn Ring weighs 5.5 g in size 17; the Brutalism V.1 Ring, among the heaviest rings STRUGA makes, 11.5 g. The alloy carries that mass without going out of shape; only the surface keeps moving — dark in the recesses, bright where the hand rubs it.

Why does 925 silver tarnish?

Because silver reacts with sulphur: the dark film is silver sulphide. The sulphur comes from air, skin, cosmetics, rubber and some papers. On 925 the film builds faster than on 999 because of the copper. It passes from pinkish and brown to dark grey and black.

Silver darkens fastest with creams and perfume, in humid salty air and next to rubber bands; slowest in a closed box. What that darkening actually is — and how deliberate oxidation differs from blackening — is covered in Living Metal, our patina guide; silver left to darken without a coating is on the Living Silver page.

The takeaway is simple: tarnish does not point to a fake. If anything, «silver» that stays mirror-bright for years with no care is worth checking — it may be rhodium-plated, or not silver at all.

How can you tell if silver is really 925?

At home you can rule out a crude fake, but you cannot confirm fineness. A magnet catches a steel core under plating: sterling does not stick, although nickel silver does not either. Scales and a glass of water give density — but only for a solid piece without stones or hollows, and they will not tell 925 from 900.

The marks read as described above: fineness, maker, assay mark where one exists. All seven home and lab checks, with what each misses, are in our complete 925 sterling silver guide.

When does the check need a jeweller?

When you need an answer about fineness, not just «silver or not». The classic test is a small file cut in a hidden spot and a drop of nitric acid: on sterling or better it turns a cloudy cream, on plated metal it turns green. It leaves a mark, so it belongs on a jeweller's bench. Assay offices test without damage, by X-ray fluorescence.

How much silver is in a STRUGA piece?

STRUGA silver is uncoated 925, so nearly all of a piece's weight is silver. The route of an object is simple: a wax model, a silicone mould, 925 silver, hand finishing. For the international market, STRUGA objects are made in Bali, each one to order.

Below — catalogue weight and the pure silver in it, weight × 0.925. Handmade weight varies slightly from piece to piece.

Piece	Size	Weight	Pure silver	Price
BLADE ear cuff L	L	3.8 g	3.5 g	$160
Signature Links V.1 Ring	17	3.2 g	3.0 g	$144
Thorn Ring	17	5.5 g	5.1 g	$212
Brutalism V.1 Ring	17	11.5 g	10.6 g	$458
THORN chain	50 cm	13 g	12.0 g	$275
BLADE Big Links Bracelet	23 cm	85 g	78.6 g	$1,500

All six pieces come from the CODEX world, the brand's everyday architectural form: the THORN, BLADE, BRUTALISM and SIGNATURE ASYMMETRIC families, plain uncoated silver with no stones or inserts.

Most of the silver line arrives bright and darkens with wear; part of it is darkened in advance, at the bench. CARBON is a different material: the base is carbon, and the light insert in it is a silver-plated jewellery alloy, not silver. Those pieces carry no fineness and are not in the table.

How do you care for 925 silver?

Three rules cover almost everything. Take pieces off before the pool and before cleaning with household chemicals: chlorine darkens and attacks silver. Store them in a closed box, away from rubber bands and out of the bathroom. Clean with a soft polishing cloth and no pressure; for heavy tarnish use a silver dip, not an abrasive paste that removes metal.

The full cleaning routine, including oxidised pieces where the dark tone is part of the form, is in our guide on how to clean a sterling silver bracelet.

Where does the 925 standard come from?

From English coinage. A pound of sterling silver was struck into 240 pennies — hence «pound sterling», a measure of silver before it was the name of money. For wrought silver, a statute of Edward I in 1300 required pieces to be of sterling standard and struck with the leopard's head before they left the maker. English hallmarking starts there; the maker's mark was added in 1363 and the date letter in 1478. The origin of the word «sterling» itself is disputed: Old English steorling, «coin with a little star», is one account among several.

From there the coin and the jewelry parted ways. In 1920 British coins dropped from 925 to 500 silver, and under the Coinage Act 1946 they moved to cupro-nickel, with all such coins dated 1947. The sterling standard for wrought silver never moved: 925 then, 925 now.

Where can you see STRUGA 925 silver?

STRUGA silver pieces are 925 throughout: rings, bracelets, chains and necklaces, ear cuffs. The men's line is gathered in the men's collection. A hallmark is easiest to read on a flat plate — the one a signet ring in 925 silver carries. Every piece is made to order and ships worldwide.