Two scales, one meaning
Gold purity is written either in karats (parts of gold out of 24) or in fineness (parts of gold out of 1,000). The karat scale is the older jewellers' way; fineness is what refiners, mints and assay offices use. The table lines them up.
| Karat | Fineness | Gold content | Where you meet it |
|---|---|---|---|
| 24K | 999.9 | 99.99% | Investment bars and coins |
| 24K | 999 | 99.9% | Some coins, some Asian jewellery |
| 22K | 916 | 91.7% | Sovereigns, Krugerrands, South Asian and Middle Eastern jewellery |
| 18K | 750 | 75.0% | Fine jewellery in Europe and the US |
| 14K | 585 | 58.5% | Everyday jewellery in the US |
| 9K | 375 | 37.5% | Budget jewellery in the UK and Australia |
The decimal in 999.9 is not decoration. A refiner guarantees at least 99.99 percent gold in a "four nines" bar; 999 (three nines) guarantees 99.9 percent. The difference is tiny in metal value but it is the difference between two standards, and serious bars are stamped with the one they meet.
Why jewellery is rarely 24K
Pure gold is soft. A 24K ring bends under a firm grip and its surface scratches in weeks of daily wear. Mixing gold with copper, silver, zinc, nickel or palladium makes an alloy that holds a shape, keeps a polish and can hold a stone safely. That is why rings and chains are usually 14K or 18K: roughly 60 to 75 percent gold, the rest doing the structural work. 22K is still common where tradition values the colour and the metal content over hardness.
Bars and coins have the opposite brief. Nobody wears them; they sit in a capsule or a safe, so they can be as pure as refining allows, and their value is simple to compute from weight and fineness.
How to read a hallmark
Look inside the band of a ring, on the clasp of a chain, or on the back of a pendant. You will usually find one or more of these:
- A fineness or karat mark: 750, 585, 375, or 18K, 14K, 9K. On bars: 999.9 or 999, often with "FINE GOLD".
- A maker's or sponsor's mark: initials or a small symbol identifying who made or sold the piece.
- An assay office mark: in countries with compulsory hallmarking (the UK, Ireland, the Netherlands, Switzerland for watch cases) an independent office tests the metal and adds its own symbol, sometimes with a date letter. The United States has no assay offices; a piece stamped "14K" must legally be what it says, and the seller is responsible for it.
- A serial number on bars and on some coins, matched to an assay card.
Very small or very old pieces may carry only a fineness number, and a worn band may have lost its marks altogether. That does not make the gold fake; it just means the claim has to be checked another way.
When the stamp is not enough
A stamp can be applied to anything. If a price looks too good, or a piece came without paperwork, a jeweller can check it in minutes: an acid test scratches a tiny streak and reacts it with a known solution, and an XRF reader reads the alloy without touching the surface. Magnets are a weak test: gold is not magnetic, but neither are many base metals used in plated pieces.
At DiOro999.9 every listing states the purity and the weight, the gold is hallmarked, and bars and coins come sealed with their serial number. If you want a piece re-checked before you buy, ask; it is a fair question.