Guides
Silver alloys guide: fineness, composition, properties, marks, and testing
Silver alloys guide covering fineness, sterling and fine silver, alloy additions, gold plating, hallmarks, supplier records and testing limits.
What to take away
- Fineness states precious metal by mass, not the full alloy recipe or how the metal behaves at the bench.
- A 925 stamp means 925 parts per thousand silver under the applicable standard; the other 75 parts are not named by the number.
- A stamp, a supplier label, a bench test and a full assay are four different kinds of evidence, and none substitutes for another.
- Plate, filled construction, solder and mixed components make a surface reading unrepresentative of the whole piece.
- Keep unknown metal segregated and unheated until you have decided the operation and assessed the hazards.
What fineness actually tells you
High-purity silver is soft and ductile. Alloying changes hardness, castability, tarnish behavior and color. Two batches stamped 925 can still saw, anneal and solder differently, because the remaining elements, the temper and any prior repair differ.
Silver fineness compared
999 fine
- Purity
- 999/1000
- Hardness
- softest
- Ductility
- highest
- Tarnish
- slowest
- UK mark
- 999
958 Britannia
- Purity
- 958/1000
- Hardness
- mid
- Ductility
- high
- Tarnish
- slow
- UK mark
- 958
925 sterling
- Purity
- 925/1000
- Hardness
- hardest
- Ductility
- moderate
- Tarnish
- faster
- UK mark
- 925
Millesimal fineness expresses precious metal in parts per thousand by mass. The trade uses 999 fine silver, 958 Britannia in the UK system, and 925 sterling silver. Which descriptions are permitted depends on jurisdiction.
The UK hallmarking guidance sets out the compulsory sponsor, fineness and assay office elements of a UK hallmark, and lists recognized silver fineness marks including 800, 925, 958 and 999. That framework does not identify an unhallmarked object, and it does not govern another country.
The 75 parts the number hides
Call a supplier and ask for the exact product name. Also ask for the claimed fineness and the composition range. Request the stock form and dimensions too. Ask for the temper and the batch or lot reference. Ask for the technical sheet and the safety data sheet where they exist.
Copper is the usual addition in sterling. Proprietary alloys use other elements, and those elements decide how the metal casts and how it tarnishes.
Do not read nickel-free, lead-free, cadmium-free, recycled, hypoallergenic or food-contact suitability out of a 925 mark. The mark does not carry that information.
Solid alloy against surface coating
Silver plate is a silver surface over another material. Filled, clad, laminated and electroformed goods are built differently again. A white surface can also be nickel silver, a base-metal alloy with no silver in it at all.
Construction decides how you cut, heat, polish and repair the piece, and how you segregate the scrap. Removing a surface layer exposes a different metal. Heating can bring in old solder, coatings, fillers or adhesive.
The evidence ladder
| Evidence | What it can support | Main limit |
|---|---|---|
| Appearance | Color and visible surface condition | Many metals and coatings look alike |
| Magnet response | Presence of some strongly magnetic material | Nonmagnetic does not prove silver |
| Mark | A stamped or laser-applied claim or official mark | Can be incomplete, misread or false |
| Supplier document | What was sold and represented | Does not follow substituted stock automatically |
| Density check | Whether bulk behavior fits a range | Voids, stones and shape affect the result |
| Surface XRF | Elements near the analyzed surface | Coatings and geometry bias the reading |
| Representative assay | Composition of the tested sample | Sampling may damage the object and still needs correct selection |
No single quick check answers every question. Each rung tells you something narrower than the rung above it.
Reading a batch at the bench
Keep a bench record of how a known batch behaves. Note how it saws and files, how it work hardens, how it takes an anneal, and how the solder and flux sequence runs. Note casting porosity, how it finishes under abrasive, and how it patinates and cleans.
Those notes steer process control. They are not composition evidence. A piece that solders and tarnishes like sterling is not thereby proven sterling.
Unknown and inherited metal
Start with the paperwork and with nondestructive observation. Photograph the whole object and the marks. Photograph the joints, the wear, the exposed layers, the damage. Photograph the repairs. Record dimensions and mass before you clean anything away.
Do not scratch, acid-test, grind or heat an object until you have decided whether alteration is acceptable and whether the method is safe. Historic or high-value pieces belong with a qualified appraiser, conservator, assay office or testing laboratory suited to the question.
Labelling workshop stock
Give each alloy and batch its own labelled container, and carry that identity through the offcuts, the work in progress and the clean scrap. Keep soldered scrap, sweeps, plated material, unknown metal and contaminated waste in separate bins.
A useful label states the source, the date, the product, and the claimed fineness. It also gives the dimensions, the batch, and any known treatments. When identity is lost, downgrade the material to unknown. Do not rebuild a claim from memory.
Common questions
Does 925 always mean sterling silver?
It is the common sterling fineness claim, and it is the number most buyers recognize. Whether a particular mark is legally sufficient depends on the jurisdiction and on the full context of the piece. Confirm the requirement with the assay office or authority that governs where you sell.
Can a magnet prove an object is silver?
No. A magnet can reveal the presence of some strongly magnetic material, which is a useful negative check. Many non-silver metals are also not strongly magnetic, so passing the magnet tells you almost nothing.
Does tarnish prove silver content?
No. Tarnish is a surface reaction, and alloy, coatings, environment, cleaning and contact with other metals all change how fast it appears. Treat tarnish as a handling observation, not as a fineness test.
Should unknown scrap be melted with known sterling?
No. Keep it segregated until the composition and any contamination are resolved for the intended use. Melting unknown metal into a known batch destroys the identity of the whole batch, and no label can restore it.
In this guide
- How to identify and document an unknown silver-colored metalDocument an unknown silver-colored metal through provenance, hallmarks, construction and assay routing before any cleaning, heating or destructive testing.
- Fine silver, sterling silver, Argentium-type alloys, and silver plate comparedFine silver, sterling, Argentium-type alloys, and silver plate compared by fineness, construction, workability, heat response, repair, finish, and disclosure.
- Silver stock, hallmark, supplier, and batch-record checklistA silver stock record ties an invoice to a finished piece, so every alloy claim, hallmark and offcut stays traceable from intake to release.
- Firestain, porosity, contamination, mixed alloys, and misleading marksSilver problems guide for diagnosing firestain, porosity, contaminated stock, mixed alloys, plated surfaces, and misleading marks before repair or remelting.
- Tracing an inherited silver object from mark to material caseReading a worn hallmark on an inherited silver object starts with photographs, not polish, and separates what a mark shows from what an assay proves.
