Pure in principle, measured in practice
Carat is a ratio: 24 parts gold in 24. Because refining cannot remove every trace element, marks state measured fineness instead — 999 for three nines, 999.9 for four nines. Treat 24ct as a description and the fineness mark as the specification.
What pure gold is like
- Deep, slightly orange yellow — noticeably richer than 18ct.
- Soft enough to mark with a fingernail on thin sections.
- Highly malleable, which is why it is used for leaf and wire.
- Does not tarnish, corrode or react with skin.
Where it is used
Investment bars, modern bullion coins such as one ounce Britannias, electronics, dentistry and gold leaf. In jewellery it appears mainly in markets where gold is bought as savings, usually as plain chain.
What does 999 mean on gold?
999 means fine gold: 999 parts gold per 1,000, or 99.9% pure. It appears on investment bars, on modern bullion coins and occasionally on high purity jewellery. Marks of 999.9 indicate four nines fine gold, refined to 99.99% purity.
999, 24 carat and fine gold
24 carat describes gold with no deliberate alloy content. In practice refining leaves trace impurities, so the mark states what was actually achieved: 999 or 999.9.
Bars and coins are marked, not hallmarked
Investment bars and bullion coins sit outside the UK hallmarking system. A refiner stamps weight, fineness, a serial number and its own name; a mint guarantees the content of the coins it strikes. The absence of an assay office mark on a bar is normal and expected — see UK gold hallmarks explained.
Why jewellery is rarely 999
Pure gold is too soft for most jewellery. It bends under everyday handling and will not hold a stone securely, which is why alloys from 9ct to 22ct exist. Where 999 jewellery does appear it is usually plain chain or a pendant intended as a store of value.
Care with high purity claims
A 999 stamp on an item that behaves nothing like fine gold — light, hard, sharply detailed — warrants scrutiny. A stamp on its own is the maker's claim rather than an independent guarantee: read UK gold hallmarks explained.
Gold Up has not yet confirmed whether it buys bars or bullion coins. Please ask first.
How purity translates into value
Fine gold content is effectively the whole weight, so 24ct carries the highest metal value per gram of any standard. Convert between standards with the gold purity conversion chart, and note that bars and coins are traded differently from scrap jewellery.
Gold Up does not buy bars or bullion coins.
