Value is not guessed. It is measured.

The carat scale: purity in twenty-fourths

Carat expresses how much of an alloy is gold, as a fraction of 24. Pure gold is 24 carat; a 9ct alloy is nine parts gold and fifteen parts other metals. The remainder — usually copper, silver or zinc — exists for hardness and colour, and it carries no precious-metal value. This single fact explains most of the surprises first-time sellers meet: a chunky 9ct chain can be outvalued by a delicate 22ct bangle, because carat multiplies weight before the market price ever enters the calculation.

One warning about the word itself: carat with a C measures gold purity, while karat is the American spelling of the same thing — but carat applied to gemstones is a unit of weight (0.2 grams), not purity. A “2-carat ring” in a jeweller's window is describing its diamond, not its gold.

Millesimal fineness: the same truth in thousandths

Modern marks usually state purity in parts per thousand. The mapping to carats is fixed and worth knowing by heart, because the number stamped inside your ring band is almost certainly one of these:

A ring stamped 750 and a ring sold as 18ct are making exactly the same claim. Continental jewellery leans on the millesimal numbers; older British pieces often carry the carat figure alongside. Silver uses the same system — sterling is 925, and continental grades such as 800 and 835 are common in inherited cutlery and tableware.

Hallmarks: the claim, witnessed

A hallmark is a set of marks struck into a piece recording its fineness — and, in full hallmarking systems, the assay office that tested it and the sponsor who submitted it. Look inside ring bands, on clasps and jump rings, on the reverse of pendants, and near the rims of cups and candlesticks.

Plenty of genuine gold carries no hallmark at all. Marks wear away with decades of skin contact; pieces made before marking requirements, or in countries where marking is not customary, never had them; and small items are often exempt below certain weights. An unmarked piece is therefore not a red flag — it simply means fineness must be established by examination rather than read off the metal. The reverse caution also applies: a stamp is a claim, and claims are tested. Worn marks misread, plated pieces imitate solid ones, and occasionally a stamp is simply wrong.

How purity is actually verified

The trade has a ladder of tests, ordered by how much they disturb the piece. Reading the hallmark under magnification is the first step. Density checks exploit gold's unusual heaviness. Touchstone and acid testing read how the alloy responds at the surface. Electronic and X-ray fluorescence instruments estimate composition without marking the piece at all. Serious assessment combines methods rather than trusting one, because each has blind spots — and plating is specifically designed to fool the quick look.

Troy weight: why your scales disagree

Precious metals are weighed in troy ounces. One troy ounce is 31.1035 grams — roughly ten per cent heavier than the 28.3495- gram avoirdupois ounce used for everyday goods. This is the single most common source of confusion at any counter: two people quote “an ounce”, mean different units, and believe they disagree about the metal when they only disagree about the dictionary. Kitchen scales also drift and round; trade scales are calibrated and read to fractions of a gram. When your reading at home differs slightly from the counter reading in front of you, the unit and the instrument are almost always the explanation.

The gram sidesteps the whole problem, which is why itemised assessments usually speak in grams: a stated weight in grams, times a fineness, times a per-gram reference, is arithmetic anyone can check on their phone.

What is deliberately excluded from the weight

Stones, clasps, springs, pins, solder and cores all add mass without adding precious metal. A proper valuation separates them: gemstones are allowed for rather than bought as gold, and steel mechanisms are excluded openly. This is why an itemised figure and a single lump-sum figure for the same pile can differ considerably — and why the itemised one deserves more of your trust. What that assessment looks like in practice, stage by stage, is covered in how it works; what each category of item is assessed for is in what we buy.

The fifth factor: the reference price

Weight and purity are properties of your metal. The reference price is a property of the day: precious metals trade continuously, and any figure you are offered relates to the market at the moment of assessment. The practical consequence is simple — a valuation is a measurement with a timestamp, not a permanent property of the piece. The measured facts (weight, fineness) stay true; the money they convert to moves with the market.