Gold Purity Explained: 999.9, 22k, 18k and 14k — and What the Stamps Mean

Gold purity is expressed in two systems that say the same thing two ways: karats, which count parts of gold out of 24, and millesimal fineness, which counts parts per thousand. Pure gold is 24 karat, or 999 fine; 18 karat is 750 fine (75% gold); 14 karat is 585 fine. Neither higher nor lower is "better" in the abstract — purity trades richness of color and value density against hardness and durability, and the right choice depends entirely on what the piece has to survive. Here is the whole system, and how to read the stamps.

How do karats and fineness map to each other?

Karat	Fineness	Gold content	Typical use
24k	999–999.9	~99.9%	Investment bars and coins; too soft for daily-wear jewellery
22k	916	91.6%	High-purity jewellery traditions; rich color, softer wear
18k	750	75.0%	The fine-jewellery standard: deep color with workable strength
14k	585	58.5%	Durable daily-wear jewellery; paler, harder, more affordable
10k	417	41.7%	The US legal minimum to be sold as gold

The arithmetic is direct: karats ÷ 24 = gold fraction. Eighteen twenty-fourths is 0.750 — hence "750" inside an 18k ring. Once you hold that conversion, every stamp in the case reads itself.

Why isn't purer always better?

Because pure gold is soft. A 24k ring worn daily will scratch, dent and lose its shape — softness is why high-purity gold lives mostly in bars, coins, and jewellery traditions where pieces are worn occasionally and remade generationally. Alloying gold with other metals is not adulteration; it is engineering. The other metals contribute hardness, spring, and color control, which is why the fine-jewellery world settled on 18k as its center of gravity: enough gold for depth of color and value, enough alloy to hold a setting closed around a stone for decades.

This is also why an honest atelier asks how a piece will live before recommending purity — a daily ring and an occasion piece have different right answers. It is one of the first questions in a bespoke commission.

What do the color names — yellow, white, rose — mean for purity?

Nothing, and that surprises people. Color comes from the alloying metals, not the gold fraction: copper leans the mix rose, white metals lean it pale, and classic yellow keeps the balance. An 18k rose ring and an 18k yellow ring contain identical gold — 750 parts per thousand — wearing different partners. Two practical notes: white gold is routinely plated with rhodium for brightness, and that surface renews at service; and because alloy recipes vary, two "yellow gold" pieces can sit a shade apart. Neither is a purity question; both are normal.

How do you read the stamps on a real piece?

Look inside the band or on the clasp for the hallmarks — tiny stamps that carry the piece's claims:

1. The fineness or karat mark — "750" or "18k", "585" or "14k". This is the purity claim.
2. The maker's or sponsor's mark — who stands behind that claim.
3. Assay marks, where present — some countries' systems add marks showing the purity was independently tested; conventions differ by country and era.

Two honest cautions. First, a stamp is a claim, not a guarantee — stamps can be faked, which is why who sold you the piece matters more than what is punched into it. Second, absence of a stamp on an older or reworked piece does not condemn it; it means the purity should be established by testing rather than by reading.

What does assay actually mean?

Testing — determining what a metal actually is, rather than what it claims. Methods range from surface tests to instrumental analysis, and serious trade in precious metals runs on it: bars carry assay certification, and reputable dealers verify rather than assume. It is the metals-desk equivalent of the watch side's written condition report — the document that turns a claim into a checkable fact. The Time Vault trades only in certified, traceable metals for exactly this reason: every bar, ingot and stone certified and traceable before it enters the workshop or the case.

How is purity actually tested at a bench?

When a stamp is absent, worn, or doubted, purity is established rather than assumed, and the methods form a ladder of confidence. At the simple end sit surface tests — touchstone and acid work that a trained bench performs in minutes, reliable enough for screening but reading only the surface. Above them, electronic and X-ray fluorescence instruments read composition without harming the piece, and are the working standard of serious trade. At the top, fire assay — the ancient, destructive, definitive method — remains the reference against which everything else is calibrated, used for bullion rather than finished jewellery for the obvious reason that it consumes a sample.

Two things follow for an owner. First, non-destructive testing means there is no reason to accept uncertainty about a piece you own — an afternoon at a competent bench settles it. Second, surface readings can be fooled by heavy plating over base metal, which is precisely why who tests matters as much as what the test says: a bench that knows the failure modes tests accordingly.

Does higher purity need different care?

Yes — care should scale with softness. High-karat pieces (22k and up) pick up fine scratches and small deformations from ordinary life: worn beside harder jewellery, they lose; stored loose in a drawer, they remember every neighbour. The practical rules are short: store soft gold separately, ideally in cloth; take high-purity rings off for gym, garden and gloves; and let polishing be rare and professional, because every polish removes metal — the same logic that makes over-polished watch cases a condition-report line item. Lower-karat pieces forgive more, which is exactly why they exist. None of this is fragility to fear — gold does not tarnish or corrode in normal wear — it is simply the maintenance grammar of a metal prized partly because it is soft enough to work beautifully.

How does purity relate to price?

Directly but not simply. The gold content of a piece tracks purity and weight against the spot price — which moves constantly; the maison publishes live spot prices for gold, silver, platinum and palladium. But a finished piece of jewellery is not a bar: its price carries the work, the stones, and the making. Two rules of thumb keep buyers oriented: melt value is a floor, never the value of a crafted piece; and spot is an index, never the number on a dealing ticket — the difference is covered in why spot price is not the price you pay.

Frequently asked questions

Is 18k gold "real gold"?

Completely — 18k is 75% pure gold and is the standard of the fine-jewellery world. "Real" versus "fake" is about honesty of the stamp and the seller, not about the karat number.

Which purity is best for an engagement ring?

Most fine engagement rings are made in 18k gold or platinum: enough hardness to hold a stone securely for daily wear, with the color and substance the occasion deserves. 14k is a legitimate choice when durability and budget lead. The honest answer depends on the wearer's hands and habits — which is a design conversation, not a chart lookup.

Does higher karat gold look different?

Yes — richer and warmer as purity rises, because less alloy dilutes the color. The difference between 14k and 18k yellow is visible side by side; between 18k and 22k, unmistakable.

What's the difference between gold-plated and solid gold?

Everything. A karat stamp on solid gold describes the whole metal; plating is a micro-thin gold surface over another metal entirely, and must be marked as such. Plated pieces are jewellery, not gold — their gold content is negligible.

Is platinum purer than gold?

Differently measured: jewellery platinum is typically 950 fine — 95% pure — higher fineness than 18k gold's 750, in a metal that is also denser and naturally white. Whether it suits a piece better than gold is a design and wear question; the maison works in both, certified.

Can The Time Vault test gold I already own?

Assessment of client metals — inherited pieces, stones, gold for reworking — is part of the atelier's intake, by appointment at 37 W 47th St. Bring what documentation exists; certification and traceability are established before any piece enters a commission.

Why do some countries prefer different karats?

Tradition and climate of use, mostly: several jewellery cultures center on 22k for its color and ceremonial weight, much of Europe and America settled on 18k and 14k for durability in daily wear. None of these is a quality verdict — they are different answers to the same trade-off, which is why an atelier asks how a piece will live before choosing its metal.