No single gold test is conclusive on its own. A hallmark can be forged, a magnet only rules out obviously magnetic fakes, and acid only tests the surface. Shops that buy gold every day layer tests: inspect the hallmark, weigh the piece, run a magnet pass, then confirm purity with acid, an electronic tester, or an XRF analyzer before quoting a price based on weight and karat.
With gold prices at levels that pull a steady stream of sellers through the door, more counter staff than ever are being asked to judge a piece in front of a waiting customer. This guide covers the tests professionals actually use, in the order they use them, and how the scrap value math works once you know weight and purity.
Step 1: Read the Hallmark, but Never Trust It Alone
Most gold jewelry carries a purity stamp, usually inside a ring band or on the clasp of a chain. You will see either karat marks or millesimal fineness numbers:
- 10K or 417: 41.7 percent gold, the legal minimum to be sold as gold in the United States
- 14K or 585: 58.5 percent gold, the most common purity in American jewelry
- 18K or 750: 75 percent gold
- 22K or 916: 91.6 percent gold, common in jewelry from South Asia and the Middle East
- 24K or 999: essentially pure gold, mostly bullion and some imported jewelry
Also watch for marks that mean the piece is not solid gold at all: GP (gold plated), GF (gold filled), HGE (heavy gold electroplate), and RGP (rolled gold plate). A hallmark is a claim, not proof. Counterfeit stamps are common, which is why the hallmark only tells you what to verify next.
Step 2: Weigh It and Run the Magnet Pass
Weigh the piece on a calibrated gram scale. You need the weight for pricing anyway, and weight is itself a signal: gold is dense, and a piece that feels light for its size deserves extra scrutiny.
Then pass a strong neodymium magnet over it. Gold is not magnetic. If the piece jumps to the magnet, it has significant ferrous content and is not solid gold. Be careful with the reverse conclusion: plenty of fakes use non-magnetic metals like brass and copper, so passing the magnet test proves nothing by itself. It is a thirty second screen that catches the crudest fakes, nothing more.
Step 3: Confirm Purity With a Real Test
Acid testing
The classic pawn counter method. Rub the piece on a testing stone to leave a streak of metal, then apply the acid matched to the karat you are testing for. If the streak survives 14K acid but dissolves under 18K acid, you are looking at 14K gold. Acid kits are inexpensive and accurate for surface testing, but they only test the surface. On a thick plated piece, the streak can test as gold while the core is base metal, which is why many shops file a small notch in an inconspicuous spot before testing a suspect piece.
Electronic testers
Electronic gold testers measure electrical conductivity through a probe and read out an estimated karat in seconds without marking the piece. They are fast, easy to train staff on, and good for high volume screening. Their weakness is the same as acid: heavy plating can fool the reading, and results near karat boundaries deserve a second test.
XRF analyzers
X-ray fluorescence analyzers are the standard for serious gold buying operations. Point the device at the piece and it reports the full elemental breakdown, gold percentage included, in seconds, without damaging anything. XRF still reads primarily the surface layer, so a deliberately thick-plated bar can require a deeper check, but for jewelry it is the fastest, most defensible reading you can get at the counter. The tradeoff is cost: an XRF unit is a four to five figure investment that typically makes sense once your gold volume is steady.
Specific gravity
The oldest test in the book: weigh the piece dry, weigh it suspended in water, and calculate density. Pure gold has a density around 19.3 grams per cubic centimeter, and each karat range has a predictable band. It is slow and awkward with stone-set jewelry, but it tests the whole piece rather than the surface, which makes it a useful tiebreaker on suspect bars and heavy pieces.
How to Calculate What the Gold Is Worth
Once you trust the weight and the karat, melt value is arithmetic:
- Convert purity. Karat divided by 24 gives you gold content: 14K is 58.3 percent, 18K is 75 percent.
- Get the spot price per gram. Spot gold is quoted per troy ounce; divide by 31.1 to get the per gram price.
- Multiply. Weight in grams, times purity, times spot per gram, equals melt value.
A worked example: a 20 gram 14K chain is 20 x 0.583 = 11.66 grams of pure gold. At any given spot price, that number times the per gram price is the melt value, and your buy offer is a percentage of it that covers your margin and refining costs. Shops that track every buy against spot, by karat, know exactly what their gold margin is; shops that quote from memory usually do not. With prices moving the way they have, repricing your offers against live spot matters more than it used to, something we covered in depth in our guide to repricing your pawn loan book when gold hits record highs.
Red Flags at the Gold Counter
- Hallmark and test disagree. A piece stamped 18K that tests 14K or lower is either counterfeit-stamped or plated. Price it by the test, never the stamp.
- Seams, flaking, or color change at wear points. Plating wears thin on edges and clasps first, showing base metal underneath.
- Tungsten-weight bars. Tungsten has nearly the same density as gold, which defeats the specific gravity test on bars. Buying bullion deserves XRF plus a reputable brand and intact assay packaging.
- Seller pushes back on testing. A legitimate seller expects a shop to test. Resistance to a standard acid or electronic test is information.
- Volume sellers with no story. Many states and cities require gold buyers to log purchases and report them to law enforcement; your license paperwork and local ordinances spell out exactly what applies to you. Consistent record keeping protects your license when a piece later turns out to be stolen.