The tiny letters and numbers stamped inside a ring or on a clasp are often the most useful clue a piece of jewelry gives you. They can tell you the metal, its purity, who made it and sometimes where and when it was tested. This guide decodes the common ones and explains the different kinds of marks, so you can read what you have and know how far to trust it.
Three kinds of marks
People use "hallmark" loosely for any stamp, but there are really three different things:
- Purity (fineness) marks state what the metal is and how pure it is, such as 925 or 14K.
- Maker's marks (also called sponsor's marks or trademarks) identify the company or craftsperson responsible for the piece. They might be initials, a logo or a brand name.
- Assay office marks show that an independent office tested the metal and confirmed the purity. Strictly speaking, only these make a stamp a hallmark in the traditional sense.
In the United States there is no government assay system. Manufacturers stamp purity themselves, and federal law requires a registered trademark to appear alongside a gold or silver quality mark so the responsible company can be identified. Many other countries, including the UK, Ireland, France, the Netherlands and several others, run independent assay offices.
Common stamps decoded
Purity numbers are parts per thousand, so 750 means 750 parts in 1,000, or 75%.
| Stamp | Meaning | Metal content |
|---|---|---|
| 999 | Fine silver or 24K gold (check the color) | 99.9% |
| 925, STER, STERLING | Sterling silver | 92.5% silver |
| 900, COIN | Coin silver, common in older American pieces | 90% silver |
| 800 | 800 silver, common in continental Europe | 80% silver |
| 916 / 22K | 22 karat gold | 91.6% gold |
| 750 / 18K | 18 karat gold | 75% gold |
| 585 / 14K | 14 karat gold | 58.5% gold |
| 417 / 10K | 10 karat gold, the lowest legal karat for "gold" in the US | 41.7% gold |
| 375 / 9K | 9 karat gold, common in the UK and Commonwealth | 37.5% gold |
| 14KP, 18KP | Karat "plumb": at least the stated karat | As above |
| GF | Gold-filled: a bonded gold layer over base metal | Fraction of weight |
| 1/20 12K GF | Gold-filled with a 12K layer that is 1/20 of total weight | At least 2.5% gold |
| RGP | Rolled gold plate: like gold-filled, but a thinner layer is allowed | Small |
| GP, GEP | Gold plated or gold electroplate: a thin surface layer | Very small |
| HGE | Heavy gold electroplate: a thicker plated layer | Very small |
| PT950, PLAT, 950 PLAT | Platinum | 95% platinum |
| PT900, 900 PLAT | Platinum | 90% platinum |
| PD, PD950, 950 PALL | Palladium | Usually 95% palladium |
| 950 on its own | Could be platinum, palladium or 95% silver | Needs testing |
| EP, EPNS | Electroplated (nickel silver) | Silver plating only |
| NICKEL SILVER, GERMAN SILVER, ALPACA | A copper-nickel-zinc alloy | No silver |
A few notes on reading these:
- A karat number followed by GP, GEP, HGE, RGP or GF describes the plating or layer, not the item. "18K HGE" is plated.
- Gold-filled content is the karat of the layer times its fraction of the weight: 12K is half gold, and half of 1/20 is 1/40, or 2.5% of the item's weight.
- 999 on a yellow piece usually means 24K gold; on a white piece, fine silver. A stamp alone sometimes needs the color to make sense.
- CZ or C.Z. stamped near a stone means cubic zirconia.
Maker's marks
A maker's mark can be as useful as the purity mark, especially for value. A recognized brand mark, such as a well-known jewelry house or a collectible designer, can raise a piece's value well above its metal. Collectors' reference books and online databases of makers' marks can help you identify initials and logos.
Italian gold usually carries a registration mark: a five-pointed star, a number, and a province abbreviation (for example AR for Arezzo or VI for Vicenza). It identifies the registered manufacturer and is a good sign the piece came through a regulated maker.
The UK hallmarking system, briefly
The UK has one of the oldest hallmarking systems in the world, and it is still compulsory for most precious-metal items sold there above small minimum weights. A full modern UK hallmark has:
- A sponsor's mark: the initials of the maker or importer, inside a shield.
- A fineness mark: the millesimal number, such as 925 or 750, inside a shaped shield that also indicates the metal.
- An assay office mark: the office that tested it. London uses a leopard's head, Birmingham an anchor, Sheffield a rose, and Edinburgh a castle.
Optional marks include traditional symbols such as the lion passant for sterling silver struck in England and a crown for gold, and a date letter for the year of assay. The date letter was compulsory until 1999, which is why older British pieces can often be dated precisely using published date-letter charts.
Other countries have their own systems and symbols. France, for example, has long used an eagle's head for 18K gold. If you see an unfamiliar symbol inside a shaped outline, it is often an assay or import mark worth looking up.
Why stamps can be faked
A purity stamp is a small steel punch struck into metal. It costs almost nothing, and anyone can buy one. That means:
- Counterfeit and plated pieces are often stamped 14K, 18K or 925 to look convincing.
- Genuine marks can be cut out of a scrap piece and soldered into another.
- Some legitimate pieces are mismarked, especially older or imported ones.
- Many genuine pieces have no mark at all, or the mark has worn away or been removed during resizing.
Assay office hallmarks are harder to fake convincingly and are better evidence, but even they are occasionally forged. Treat any stamp as a strong clue that still needs confirming. A jeweler's acid or XRF test settles the metal question; see how to tell if gold is real for what those involve.
Tip: photograph each stamp up close before taking a piece anywhere. Marks are easy to misread with the naked eye, and a sharp, magnified photo is easier to compare against reference charts. If you scan a piece with AI Jewelry, include a clear shot of the stamp so it can factor the mark into its description of the metal.
What a stamp does not tell you
Even a genuine purity mark leaves out a lot:
- Stones. A 14K mark says nothing about whether the diamond in the setting is natural, lab-grown or a simulant. See how to tell if a diamond is real.
- Weight. Value depends on how much metal there is, which you need a scale for.
- Age. Except for date letters, most marks do not date a piece. Style, construction and maker's marks help more.
- Value. A plain 9K ring and a signed designer piece in 9K can differ enormously in price.
When you are ready to put a number on a piece, the guide to how much your jewelry is worth explains melt value, resale and appraisals.