The shape of the hallmark tells you the metal. The number tells you the purity in parts per thousand.

A gold hallmark of 585 means that 585 parts per thousand of the item’s weight, or 58.5 per cent, is pure gold. A silver hallmark of 925 means 92.5 per cent in the same way.

Karats say the same thing differently: 18 karat gold is 18 parts out of 24, which is 750 in parts per thousand.

On gold hallmarked in Finland the purity number sits inside an oval frame. A rectangle means silver, a diamond shape means platinum.

585 and 750 are the purities you will see most often. Gold bought abroad also turns up as 375, 417, 875 and 916.

The mark is usually inside the ring band or close to the clasp on a chain. It is small, and your phone camera’s zoom helps.

No mark anywhere? Choose 375. The estimate then stays on the cautious side, and if we measure a higher purity we pay for the higher one.

A kitchen scale is not as precise as the calibrated scales we use. A few tenths of a gram either way is normal and does no harm.

Weigh everything together if it is all the same purity. Weigh separately only where the purities differ.

No scale? Rough weights: a ring 2–5 g, a thin chain 1–3 g, a heavy chain 15–50 g, a pendant 0.5–3 g, a pair of earrings 0.5–3 g. A ring’s width in millimetres is often close to its weight in grams.

Stones, pearls and anything that is not gold do not count, so leave them out when you weigh. We remove stones and return them to you if you want them. Whether they come out cleanly depends on the setting and the condition of the piece, so we cannot promise it for every item.