That small "18K" stamp inside your ring or on the back of your pendant isn't decoration. It's a legal verification that the piece is 18-karat gold, meaning 75% pure gold by weight.
Here's how to read every gold hallmark, where to find it, and what it means if there's no stamp at all.
The 18K stamp, explained
The "K" stands for karat, a measure of gold purity. Pure gold is 24K. So:
18K = 18 parts gold out of 24 = 75% pure gold.
The other 25% of the piece is alloy, usually copper, silver, palladium, or zinc, added to make the metal hard enough to wear daily. (Pure 24K gold is too soft to hold a setting or survive normal handling.)
So if you see "18K" stamped on a piece, the seller is making a legal claim that 75% of the metal in your hand is pure gold. In most countries, falsifying this stamp is a regulated offense.
Every gold hallmark you'll see, decoded
Beyond "18K," you might see any of these stamps on jewelry. Here's what each one means:
| Stamp | Meaning | Pure gold % |
|---|---|---|
| 24K / 999 | Pure gold (rare in jewelry, too soft) | 100% |
| 22K / 916 | 22-karat gold (common in South Asian / Middle Eastern jewelry) | 91.6% |
| 18K / 18KT / 750 | 18-karat gold (global benchmark for fine jewelry) | 75% |
| 14K / 14KT / 585 | 14-karat gold (US market default) | 58.5% |
| 10K / 417 | 10-karat gold (US legal minimum for "gold") | 41.7% |
| 9K / 375 | 9-karat gold (UK budget category) | 37.5% |
| GF / Gold Filled | Base metal with bonded gold layer (~5% gold by weight) | Not solid gold |
| GP / RGP / HGP | Gold plated / rolled gold plated / heavy gold plated | Trace gold |
| GE / EP | Gold electroplated | Trace gold |
| Vermeil | Sterling silver with gold plating (must be at least 2.5 microns thick in the US) | Not solid gold |
| 925 | Sterling silver (not gold) | 0% gold |
The three you'll see most on actual fine jewelry: 18K, 14K, and the international fineness marks (750, 585).
Why both "18K" and "750" exist
They're the same thing in two different number systems.
- "18K" is the American/British convention, based on parts out of 24
- "750" is the international fineness mark, based on parts per 1,000
18 / 24 = 0.75 = 75% = 750 / 1000.
European, Middle Eastern, Asian, and South American jewelers almost always use the 750 stamp. American jewelers often use both 18K and 750 (or just 18K). British jewelers historically used "18ct" (an older spelling of karat, "ct" for carat). All four mean the same thing.
For more on this specifically, read what 750 gold means.
Where to find the hallmark on different pieces
Hallmarks are stamped where they don't interfere with the design but can still be verified. Common locations:
- Rings: inside the band (you may need to look closely, the stamp is tiny)
- Necklace chains: on the clasp or on a small tag attached near the clasp
- Pendants: on the back of the pendant, or on the bail (the loop that connects it to the chain)
- Earrings: on the post (for studs) or on the inside of the hoop (for hoops)
- Bracelets: on the clasp or on a small tag near the clasp
- Cuffs and bangles: on the inside of the band, usually toward one end
If you can't find a stamp, try a jeweler's loupe (10x magnification) or a strong magnifying glass in good light. Italian pieces also usually carry a small diamond-shaped maker's mark alongside the 750 stamp, a registered identifier of the goldsmith who made it.
What if there's no hallmark at all?
A missing hallmark on a piece sold as 18K is a red flag, but not always a deal-breaker.
Legitimate reasons a piece might lack a hallmark:
- Very old or vintage pieces made before modern hallmarking laws existed
- Custom pieces from small artisans who haven't registered a maker's mark
- Worn-down stamps on heavily used heirloom pieces
Not-legitimate reasons:
- The piece isn't really 18K. The most common explanation.
- The seller has no way to prove the karat.
If you're buying new from any seller and there's no hallmark, ask why. A trustworthy seller will explain, or refuse to sell it as 18K. An untrustworthy one will hedge.
You can also get any piece tested at a jeweler, they'll use an electronic gold tester (about 30 seconds) or acid test (slightly more invasive but very accurate) to confirm the actual karat.
What "18K" doesn't tell you
The 18K stamp confirms the gold purity. It doesn't tell you:
- Whether the piece is solid or plated. "18K Plated" or "18K GP" means the piece has a layer of 18K over a base metal. Look for "solid" wording in addition to the karat stamp.
- What's in the 25% alloy. Whether the alloy includes nickel (an allergy risk) varies by maker. Reputable brands disclose their alloy composition.
- The piece's weight. Two 18K rings can have wildly different gold content depending on size and thickness.
These are the questions to ask alongside the stamp. We cover the full buying checklist in the complete guide to 18K solid gold jewelry.
The bottom line
"18K" on jewelry means 18-karat gold, 75% pure gold by weight. It's a legal verification stamp, equivalent to "750" in international convention. Always verify the stamp is present, look for "solid" alongside it (not plated or filled), and ask the seller for gram weight and alloy composition.
Every Ange Hadid piece carries the 750 hallmark plus the maker's mark of the Mediterranean atelier that produced it. You can see the stamp in the close-up photos on every product page.
FAQ
Is 18K the highest gold purity in jewelry?
No, 22K and 24K are higher purity. But 18K is the highest practical purity for daily-wear jewelry. 22K is softer and harder to set stones in; 24K is too soft for most jewelry applications.
Does "18K" stamped on jewelry mean it's real gold?
The stamp is a legal claim that the piece is 18-karat gold. Reputable brands honor that claim; fraudulent sellers don't.
What's the difference between 18K and 18KT?
None. "18KT" is just an alternative spelling, "KT" instead of "K" for karat. Both mean the same thing: 75% pure gold.
What does "18K Italy" stamped on jewelry mean?
It means the piece is 18-karat gold (75% pure) and was made in Italy. Italian-made 18K is typically considered top-tier because of Italy's strict hallmarking laws and centuries of goldsmithing tradition. Look for the 750 stamp plus a maker's mark in a diamond-shaped cartouche alongside the "Italy" stamp.
What does "18K HGE" mean?
HGE stands for Heavy Gold Electroplate. It's a plating method, not solid gold. Avoid if you're buying for daily wear, the plating wears off.
