Inside the goldsmith’s workshop
From sketch and wax model to casting, setting and polish: how a piece of fine jewellery is made, and what the numbers stamped on gold really mean.
Tool
Gold Content Calculator
Enter the weight and the karat or hallmark number of a piece and see how much fine gold it contains.
Karats and fineness
Gold jewellery is almost always an alloy. The karat system divides the whole into 24 parts: 18 karat gold is 18 parts gold and 6 parts other metals, which is 75 per cent. Hallmarks express the same idea in parts per thousand, so 18 karat is stamped 750, 14 karat 585 and 9 karat 375. The calculator multiplies the weight by that share to give the fine gold content.
Troy ounces and pennyweights
Precious metals are weighed in troy units. One troy ounce is 31.1035 grams, a little heavier than the ordinary ounce of 28.35 grams, and one pennyweight is a twentieth of a troy ounce, about 1.555 grams. Prices for gold bullion are usually quoted per troy ounce.
What the value means
If you enter a price, the calculator shows the value of the fine gold only. A finished jewel is worth far more or sometimes less than its metal: design, craftsmanship, stones, maker, condition and provenance all count, and a buyer of scrap gold deducts costs for refining. We show no live prices and store nothing you enter.
Questions
Why is 14 karat stamped 585 and not 583?
Fourteen twenty-fourths is 58.33 per cent, but the hallmark sets a minimum standard, and 585 gives a small safety margin for the alloy. The calculator uses the stamped fineness, which is what a piece must at least contain.
Does white gold contain less gold?
No. An 18 karat white gold ring contains 75 per cent gold like a yellow one; only the other 25 per cent changes. White gold uses white metals such as palladium or silver in the alloy and is often plated with rhodium for a bright finish.
Read more
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