Start with the stamp: 10K, 14K, 18K or 417, 585, 750 means solid gold; GP, GF, HGE or RGP means plated or filled. Then try simple home tests.
A karat number claims solid gold; it doesn’t prove it, and the rest of this guide shows how to check that claim. It covers jewelry and small personal pieces, not bullion bars or coins.
You’re likely to find two kinds of stamp: karat or fineness numbers, which claim gold all the way through, and letter codes such as GP, GF, HGE and RGP, which mean a gold layer over another metal. The definitions come from the Federal Trade Commission’s jewelry guides in 16 CFR 23.3 and the National Gold and Silver Stamping Act, and the UK fineness standards from the Assay Office Birmingham.
Home tests are ranked from harmless to destructive, using the GIA touchstone method and a GIA comparison of gold testing techniques. A stamp alone is a claim, not a lab result, and no home test measures karat precisely.
Where is the stamp on gold jewelry?
The stamp sits where it won’t show when the piece is worn: inside a ring shank, on the tongue or tab of a clasp, on an earring post, on the bail of a pendant or on the back of a brooch. Chains usually carry it on the clasp or on a small tag next to it.
Clean the area with warm soapy water and a soft brush first. Dirt fills shallow punches, and a worn 4 can read as a 1 on an old ring. A 10x loupe and a phone flashlight held low across the surface make shallow marks much easier to read.
Write down every character you see, in order, before you start interpreting. A gold ring often carries a karat or fineness number, a maker’s name or trademark and sometimes extra symbols. Our guide to identifying hallmarks explains the same reading routine for silver, and it works just as well on gold.
A missing stamp doesn’t mean a piece is fake. Old rings get resized and the mark can be cut away, and small pieces were often left unmarked. It simply means you’ll lean harder on testing later.
What do karat and fineness numbers mean?
A karat mark (10K, 14K, 18K) or a three digit fineness number (417, 585, 750) states how much pure gold is in the alloy. Karats count parts out of 24; fineness counts parts out of 1,000. Both describe the same thing in two systems.
The Assay Office Birmingham lists the UK gold standards as 375, 585, 750, 916, 990 and 999. You’ll also see 417, the fineness equivalent of 10 karat, which is common on American jewelry.
| Stamp | Fineness | Pure gold share |
|---|---|---|
| 9K or 9ct | 375 | 37.5% |
| 10K | 417 | about 41.7% |
| 14K | 585 | 58.5% |
| 18K | 750 | 75% |
| 22K | 916 | 91.6% |
| 24K | 990 or 999 | 99% or 99.9% |
Notice that 585 is slightly above the arithmetic 14/24 (58.3%). That margin matters because US law lets the real fineness fall short of the mark by only a few thousandths: under 15 U.S.C. 295, no more than three thousandths for the gold itself, and seven thousandths for most articles tested whole with their solder.
For the British town marks that appear beside these numbers, our hallmarks chart shows the anchor, leopard’s head, rose and castle.
What do GP, GF, HGE and RGP mean?
These letters mean the piece is base metal with a gold layer, not gold all the way through. The FTC jewelry guides, in 16 CFR 23.3 and the vermeil section that follows it, set the minimum for each term, and every layer must be at least 10 karat.
| Mark | What it means | Minimum gold layer |
|---|---|---|
| GP | Gold plate: either electroplate or a mechanically bonded layer | Electroplate: 0.175 microns of fine gold equivalent; bonded: at least 1/40 of the total metal weight |
| HGE | Heavy gold electroplate | 2.5 microns of fine gold equivalent |
| GF or 1/20 GF | Gold filled, layer bonded mechanically | 1/20 of the total metal weight |
| RGP | Rolled gold plate, thinner bonded layer | At least 1/40 of the total metal weight; the fraction appears in the mark (for example 1/40 12K RGP) |
| Vermeil | Gold over sterling silver | 2.5 microns over a sterling base |
GP is the one ambiguous code. Under the FTC guides, “gold plate” can describe either an electroplated layer or a mechanically bonded one, so the letters alone don’t tell you which; GEP is the unambiguous mark for gold electroplate.
The weight math shows the gap. A 4 gram ring stamped 14K holds 4 x 0.585 = 2.34 grams of pure gold. Stamped 1/20 14K GF, a 4 gram ring holds 4 x 0.05 x 0.585 = 0.117 grams. Both look the same on a finger; one has twenty times the gold of the other.
Watch the order of the characters. “14K GF” isn’t solid 14K; the GF changes the meaning of everything before it. Silver plate plays the same trick with marks that imitate sterling, as our article on plate marks that look like sterling explains.
To read the marks on your own piece, Antique Identifier – Antiqly identifies a hallmark from a photo, on iPhone and Android.
Why doesn’t a stamp settle it on its own?
A stamp is a claim, and who made the claim depends on the country. In the US, the maker strikes the karat mark itself; nobody independent tests it before sale. Under 15 U.S.C. 297, anyone who stamps a quality mark on gold must also apply their registered trademark or their name, so a karat number with no maker’s mark beside it deserves suspicion.
In the UK, gold items of 1 gram and over must be hallmarked by an independent assay office, according to the Assay Office Birmingham. A full UK hallmark has a sponsor’s mark, a fineness mark and an assay office mark. On a British gold ring, an anchor beside 375 or 750 means Birmingham tested it, and our Birmingham hallmarks guide shows how that anchor changed over time.
Even a correct looking stamp can mislead. Plated costume pieces can be stamped 14K or 18K with no trademark beside the number. Decorative marks on gilt pieces can also imitate official ones, the same trick explained in pseudo-hallmarks on silver.
So read the stamp first, then check it against the physical evidence. A plain 14K with no maker’s mark on a piece that’s worn through to grey metal at the edges is a strong warning sign.
How do you test gold at home, step by step?
Home tests can rule a piece out, but they can’t confirm its karat. Work from the gentlest test to the most invasive, and stop once you have a clear answer.
What you’ll need:
- a 10x jeweler’s loupe and a phone flashlight
- a strong magnet, such as a neodymium fridge magnet
- a kitchen scale that reads to 0.1 g
- a known stamped gold piece for comparison, if you have one
- an acid test kit, gloves and goggles, only for pieces you’re willing to mark
- Read the stamp with a loupe. Note any karat or fineness number, any GP, GF, HGE or RGP, and any maker’s name or trademark.
- Check wear points. Look at the edges of a ring, the links of a chain and the corners of a clasp. A different colored metal showing through the yellow surface points to plating.
- Hold a strong magnet next to it. Gold isn’t magnetic, so a strong pull means iron or steel is present. A steel spring inside a clasp can pull too, so test the body of the piece, not only the clasp. No pull doesn’t prove gold, since brass and many other metals don’t react either.
- Compare the color and weight with a known piece. If you own a stamped 14K item from a trusted jeweler, set the two side by side. This is a rough check, not a measurement.
- Use an acid test kit only if the piece isn’t valuable as an antique. The GIA touchstone method starts with a small notch in a hidden spot and a drop of 18K test acid; a strongly bubbling green reaction indicates base metal. Wear gloves and goggles.
- Get an XRF reading if the answer matters. X-ray fluorescence, one of the methods in the GIA study below, reads the alloy without cutting the piece; ask a jeweler whether they can arrange it.
Skip the unglazed ceramic streak test on old jewelry. It works by grinding metal off the piece, and it leaves a scratch you can’t undo.
Which home tests give false answers?
Density testing is the weakest of the common methods, according to a GIA comparison, and streak and color checks share its basic flaw. They test the surface or the overall weight, and gold plating, mixed metals and stones throw them off.
A GIA study of gold testing methods compared hydrostatic weighing, touchstone testing, an electronic tester and X-ray fluorescence. It found the weighing method the least suitable of the four, and none of them reliably measured gold content within the 3 parts per thousand tolerance in US law. If trained staff with lab gear can’t get that precision, a kitchen scale and a glass of water won’t either.
Surface tests have a different weakness. Heavy plating can survive a light acid touch or a streak, which is why the GIA method cuts a notch first to reach metal below the surface. Gold filled pieces are especially tricky, because their bonded layer is thick enough to pass casual checks.
The bite test tells you little, because teeth dent many soft metals, not only gold. Treat any single test as one clue, and give the stamp and the wear pattern equal weight.
What should you do with your piece now?
Start a simple record before anything else. Photograph the stamp through a loupe or with your phone’s macro mode, then photograph the whole piece and any worn spots. Write down the weight in grams if you have a kitchen scale that reads to 0.1 g.
Next, match each character in the stamp against the two tables above. If you find GP, GF, HGE or RGP, you have your answer: it’s plated or filled, and the fraction tells you roughly how much gold is in it. Treat a karat number with no trademark as unconfirmed.
Finally, if the piece seems to be solid gold and the value matters to you, ask a jeweler for a non destructive XRF reading before you sell, insure or alter it. Don’t let a buyer file or acid test an heirloom you plan to keep.
Method and limits. This guide draws on the US Code of Federal Regulations (16 CFR 23.3), 15 U.S.C. 295 and 297, the Assay Office Birmingham and two GIA publications, all consulted in October 2026. No piece was examined in hand. The tests described can rule items out but don’t replace a laboratory assay, and nothing here is a valuation.
Where does Antiqly fit?
Antique Identifier – Antiqly works from photos, so it helps with the first step: reading the marks. You can add up to four extra photos, such as a close shot of the stamp or the back of a clasp, plus a short note to steer the identification. If a maker’s mark is visible, Antiqly describes it and gives its interpretation with a confidence level. To read the marks on a ring or chain from your phone, try https://apps.apple.com/app/apple-store/id6751417557?ppid=ae13e448-0bac-4939-a6d7-e1bc60033c24&pt=128215051&ct=sot-152&mt=8, available on iOS and Android.
Antiqly can’t measure metal. It doesn’t run a magnet, acid or XRF test, and its reading of a mark is an AI estimate that can be wrong, especially when the stamp is worn. Treat it as a second pair of eyes on the stamp, then confirm anything important with a jeweler.
Frequently asked questions
Frequently asked questions
Does 585 mean 14K gold?
Yes. 585 is the fineness mark for 14 karat gold, meaning 58.5% pure gold. That is slightly above the arithmetic 14/24, which works out to 58.3%.
Is 9ct gold real gold?
Yes. 9ct, marked 375 in the UK, is a recognised gold standard containing 37.5% gold. The Assay Office Birmingham lists 375 among the UK gold standards, alongside 585, 750, 916, 990 and 999.
Can a magnet tell if gold is real?
Only partly. Gold isn’t magnetic, so a strong pull means iron or steel is present. No pull proves nothing, because brass, copper and many plated pieces don’t react either.
Is gold filled jewelry worth anything?
It has some gold in it, but far less than solid gold. A piece marked 1/20 14K GF has about one twentieth of its weight in 14K gold, so its gold content is small.