Understanding gold karats and hallmarks

Karat = purity

Karat (written "k" in the US and "ct" in the UK) measures how much of an item is pure gold, out of 24 parts. The rest is other metals that add strength and colour.

• 24k — about 99.9% gold (stamped 999)
• 22k — about 91.6% gold (stamped 916)
• 18k — 75% gold (stamped 750)
• 14k — about 58.3% gold (often stamped 585)
• 10k — about 41.7% gold (stamped 417); the US legal minimum to be called gold
• 9ct — 37.5% gold (stamped 375); common in the UK

Reading the stamps

Look inside ring bands, on clasps, and near jump rings for small stamps. In the UK, gold over 1 gram must carry an official hallmark from an assay office, which includes the fineness number above. In the US, stamps are applied by manufacturers and are not independently assayed, so a buyer may test the metal to confirm it.

Stamps that do not mean solid gold

Some stamps mean an item is only coated or layered with gold. These contain very little gold, so most buyers offer little or nothing for them as scrap:

• GF — gold-filled (a thick layer of gold bonded to another metal)
• GP or GEP — gold-plated or gold electroplated
• HGE or HGP — heavy gold electroplate / heavy gold plate
• RGP — rolled gold plate
• Vermeil — gold-plated sterling silver

How karat changes the price

A buyer calculates value from the pure gold content: weight × purity × gold price, minus their margin. That is why 18k pieces fetch noticeably more per gram than 10k pieces of the same weight.