You are holding a gold chain or ring, and a small question creeps in: is this actually gold? Maybe you inherited it. Maybe you are buying secondhand. Maybe you just want to double check something you already own. Either way, you do not need a jeweler's loupe or years of training to get started. You just need to know where to look and what the marks mean.
In this guide, we will walk through the three checks that matter most: the stamp, the hallmark, and the acid test. By the end, you will know how to read the tiny numbers on your jewelry, spot the difference between a real mark and a fake one, and understand how professionals use acid to confirm purity in seconds.
What a Gold Stamp Actually Tells You
A gold stamp is a small engraved mark that shows how much pure gold is in the piece. You will usually find it in one of a few spots: inside a ring band, near the clasp of a necklace, or on the back of a pendant. It is often tiny, so a magnifying glass or your phone camera zoomed in can help.
Most stamps use the karat system: 10K, 14K, 18K, or 24K. The higher the number, the more pure gold is in the metal. Some pieces, especially ones made outside the US, use the millesimal fineness system instead. That means a number like 417, 585, or 750 in place of the karat.
Here is how the two systems line up:
● 10K = 41.7% gold = stamped 417
● 14K = 58.5% gold = stamped 585
● 18K = 75% gold = stamped 750
● 24K = 99.9% gold = stamped 999
At Gold Custom, every piece is stamped for purity, and we only sell solid 10K and 14K gold. We do not carry plated or filled jewelry, so if you buy from us, the stamp reflects exactly what you are wearing.
Hallmarks: The Details Beyond the Karat Number
A stamp tells you the purity. A hallmark can tell you more. Depending on where a piece was made, you might also see a maker's mark, a country of origin code, or a small logo from the manufacturer or retailer. These extra marks help trace where the piece came from and who stands behind it.
You might also come across letters like GP or GF. These are worth slowing down for, because they change everything. GP means gold plated, and GF means gold filled. Neither one is solid gold. A gold plated piece has only a thin layer of gold over a base metal, while gold filled has a thicker layer bonded to a base metal underneath. Both can look convincing at first glance, but they are not the same purchase as solid gold, and they will not hold their value the same way.
Can a Stamp or Hallmark Be Faked?
Yes, and this is the part people are often surprised by. A stamp is a strong first clue, but it is not proof on its own. Some counterfeit jewelry carries a fake "14K" or "750" stamp even though the metal underneath is mostly brass or another alloy. This is more common with pieces bought from unfamiliar online sellers, pawn shops with no return policy, or marketplaces where you cannot verify the source.
That does not mean you should ignore the stamp. It just means you should treat it as your starting point, not your final answer, especially for anything expensive. If a stamp looks fresh, oddly placed, or inconsistent with the rest of the piece, that is worth a second look before you buy.
The Acid Test: How Jewelers Confirm Purity
When a stamp is not enough, jewelers turn to the acid test. It works because gold does not react to most acids, while the base metals used in fake or lower purity jewelry do.
Here is how the process generally works:
First, the jeweler makes a small, shallow scratch on the piece, usually in a spot that will not be visible when worn. Next, they apply a drop of testing acid to the scratch. Nitric acid is common for lower karats, and a stronger mix called aqua regia is sometimes used for higher purity pieces. Then they watch what happens. If the metal holds its color and shows no reaction, that supports a real gold reading. If the scratch turns green, milky, or dissolves, the metal underneath is not what the stamp claims.
Jewelers often pair this with a touchstone, which is a small black stone used to rub the metal and read the acid reaction more clearly. Combined, these two tools give a fast, low cost way to confirm karat that has been used in the trade for generations.
Should You Try the Acid Test at Home?
You can buy gold testing kits online, and some people do use them at home. But we would rather be straight with you: this test involves real acid, it can damage the piece if done incorrectly, and it is easy to misread the result if you do not do this regularly. For a valuable ring, a family heirloom, or anything you plan to keep for years, it is worth the short trip to a professional instead.
If you want a gentler starting point before involving acid at all, a simple magnet test is a good first filter. Real gold is not magnetic, so if a piece pulls strongly toward a magnet, that is a red flag worth investigating further.
When to Trust a Professional
Stamps and hallmarks are a fast way to narrow things down. The acid test adds a stronger layer of confirmation. But for anything high value, or anything you are not 100% sure about, a jeweler with an XRF machine can read the exact gold content in seconds without leaving a mark on the piece at all. This is especially worth doing before you sell a piece, insure it, or pay a price that assumes it is solid gold.
Buying With Confidence
The easiest way to skip all of this guesswork is to buy from a source that is upfront about purity from the start. At Gold Custom, every ring, chain, and pendant we sell is solid 10K or 14K gold, clearly stamped, with no plating and no filled pieces mixed into the collection. Whether you are drawn to a classic Miami Cuban chain, a detailed Byzantine chain, a gold pendant, or a ring for everyday wear, you can check the purity for yourself the moment it arrives.
If you already own gold and want to learn more testing methods beyond stamps and acid, our full guide on how to tell if gold is real walks through additional at home checks, including the water test and the skin test.
Real gold should never be a guessing game. Once you know how to read a stamp, spot a genuine hallmark, and understand what the acid test is really checking for, you can shop and sell with a lot more confidence.