What Is an Assay Report and When Do You Need One?

Gold jewellery is sold on a number, 22 karat, 916, 750. Yet purity cannot be seen. Two bangles of identical colour and weight can differ meaningfully in gold content, and nothing about their appearance will tell you. Assaying is how the trade replaces assumption with measurement, and the assay report is the record of that measurement.

What Assaying Means

An assay is an analytical test that determines the precious-metal content of an alloy. For gold, the result is expressed as fineness, parts of gold per thousand parts of alloy, or converted into karat. Gold of 916 fineness is 91.6 per cent gold, the familiar 22 karat of South Asian jewellery; 750 corresponds to 18 karat; sterling silver is 925.

The essential point is the difference between a claim and a finding. A stamp reading 916 is a claim. An assay result of 916 is a finding.

How Metals Are Tested

Several methods coexist, chosen to balance accuracy against damage to the piece:

Method	Character
Touchstone	Traditional streak test; quick, approximate, near-non-destructive
X-ray fluorescence (XRF)	Modern instrument reading of surface composition; non-destructive
Fire assay	The long-standing high-accuracy method; destructive, so used for bullion and samples

XRF has become the everyday workhorse for finished jewellery because it is fast and leaves the piece untouched, though as a surface technique it has known limits, plated items can mislead it. The practical side of getting gold tested is covered in our guide to gold testing.

What an Assay Report States

A typical assay report identifies the item tested, the method used, the date, and the measured composition, chiefly the fineness of the precious metal. Like a gem report, it describes a specific object on a specific date, and it is silent on everything else: workmanship, gemstones and market value all sit outside its scope.

For a stone-set piece, that means three separate questions need three separate documents: the metal (assay), the stones (identification report) and the insured value (valuation).

Assay and Hallmarking

Formal hallmarking systems are built on assay: in jurisdictions that operate them, an independent office tests the metal and then strikes marks attesting to its fineness. A hallmark in such a system is therefore an assay made visible. Where no compulsory system operates, purity stamps are applied by makers and sellers themselves, and independent testing is the buyer's substitute. How the marks work, and how to read them, is the subject of our guides to hallmarking and gold hallmarks.

When to Seek an Assay

Independent testing earns its keep whenever much rests on purity: substantial gold purchases, second-hand or inherited pieces with unverified stamps, and any transaction where the price is calculated from metal weight and fineness. Ask the seller whether the piece has been independently tested, and where. A seller confident in their gold has no reason to resist a test, and verify current practice with the testing provider, since services and methods vary.