Can a silver tester or acid test prove a piece is sterling, and what do stamps show?

ZKZ Editorial TeamMain answer · Product & gemmology desk

A simple tester can suggest whether metal is silver, but it cannot reliably prove that a piece meets the 925 standard throughout. A stamp is a claim by the maker, and a legal hallmark is applied by an independent assay office in some countries. For a firm answer, use laboratory assay.

What the sources say

Fact The FTC Jewelry Guides (16 CFR 23.5) say that "Sterling Silver" or "Sterling" should only be used for an item that is at least 925/1,000ths pure silver, and describe a coated item as misleading if called silver without qualification.

Fact UK Government guidance says it is very difficult to know what an item of jewellery is made of just by looking at it or touching it, and that hallmarking protects consumers by certifying the precious metal content.

What a quick test can and cannot show

Our advice A surface test checks only the surface. A plated piece may pass on the surface and not be silver beneath, and a test mark cannot tell 900 from 925.

Our advice A stamp shows what the maker says, so ask where the stamp was applied and by whom.

It depends Better methods, such as fire assay or laboratory analysis, give a number, and some retailers use XRF for screening. Each has limits.

Better ways to check a batch

Our advice Agree an inspection plan with the factory: sample a number of pieces from each batch, send them for assay, and compare the results with the stamp. Ask for a test report that names the method and the laboratory. If the supplier resists independent testing, that is itself information you should weigh when deciding whether to place a bigger order.

Our advice Write down what any test result means before you rely on it. A passed surface test is a reason to look further, not a certificate, and a failed test on a worn piece may only mean the surface has changed.

Uncertain We have not verified the accuracy of any particular tester or test kit, and we do not recommend one.

Practical advice

Our advice For a batch, sample pieces and send them to a laboratory. For a single piece, buy from a seller who can show a hallmark or test certificate.

Related reading: What does a 925 stamp plus a maker mark prove, and what does it not prove? · 925 Sterling Silver vs Sterling Silver: Is There a Difference?

Sources

• 16 CFR 23.5, FTC Jewelry Guides: misrepresentation as to silver content
• UK Government, hallmarking guidance notes

Fact = stated by the cited source. Our advice = editorial recommendation. Uncertain / it depends = limits of what can be said in general.