How Gold Buyers Test Gold

What non-destructive testing means for your jewelry

Non-destructive testing (NDT) simply means finding out what something is made of without damaging it. For jewelry, that means no acid on the metal and no scratch or file mark for the XRF reading itself — your piece leaves the counter exactly as it arrived.

That matters most for the pieces you care about: heirlooms, engagement rings, designer jewelry and anything you might keep rather than sell. A quick, accurate XRF reading tells you what you have without leaving a mark, so you can make a decision with the facts in front of you.

Reading the hallmark first

The first step in almost any evaluation is a visual check for a hallmark — the small stamp inside a ring band, on a chain's clasp tag, or on the back of a pendant. Stamps like 10K, 14K, 18K, 585, 750 or 916 tell a buyer the manufacturer's claimed purity before any testing begins. A hallmark is a starting point, not proof, because stamps can wear smooth, be applied to gold-filled or gold-plated pieces, or occasionally be counterfeit.

Because a stamp alone is never treated as final, a careful buyer will also look at the piece under magnification for solder joints, plating wear at high-contact points like the inside of a ring, and any second stamp that might indicate a repair. All of this happens before the item ever touches a testing tool, and you should be able to watch it happen at the counter rather than in a back room.

The magnet test — a fast first filter

Pure gold and most karat gold alloys are not magnetic, so a simple rare-earth magnet test is a quick way to rule out base metals disguised as gold or heavily plated steel and iron cores. If a piece is pulled strongly toward the magnet, it is not solid gold, full stop.

The magnet test has limits: some gold-colored alloys and certain platinum-group blends are also non-magnetic, so passing this test only means an item deserves further testing — it does not confirm karat or purity on its own. Any buyer who stops at the magnet test and makes an offer is skipping steps.

Acid testing and the file test

Acid testing is one of the oldest methods still in everyday use. A small, usually unnoticeable scratch is made on an inconspicuous spot — often the inside of a ring shank — and a drop of nitric-acid-based solution calibrated to a specific karat (10K, 14K, 18K, and so on) is applied. If the gold in that scratch is at least that purity, the mark holds; if it is lower, the acid reacts and dissolves the metal, showing the buyer it does not meet that karat.

The file test is used alongside acid testing on questionable pieces, particularly plated jewelry. A fine jeweler's file removes a tiny amount of surface material so the acid tests the actual metal underneath rather than a plated layer that could give a false high reading. This two-step approach protects you as much as it protects the buyer, since it prevents a heavily plated item from being mistaken for solid gold.

Testing acids are corrosive and can injure skin and eyes or damage a piece if misused. Acid testing is a job for a trained buyer with proper equipment and ventilation, not a home experiment — if you want to know what a piece is before selling, bring it in and watch the test instead.

Electronic gold testers

Electronic gold testers take a reading from a small contact point on the item and translate it into a karat estimate, because different metals and karats respond differently. These devices are fast and generally non-destructive, making them useful for a first pass on jewelry a customer wants to keep intact, though they can be thrown off by mixed-metal alloys, unusual plating or a dirty surface.

XRF analysis: what it can and cannot tell you

XRF stands for X-ray fluorescence. An XRF analyzer directs X-rays at a small spot on the item; the atoms in that spot respond by emitting X-rays of their own at energies characteristic of each element, and the analyzer reads those signals to estimate the elemental composition — how much gold, silver, copper, zinc or other metal is present. Under ordinary jewelry-testing use it is non-destructive and needs no scratch or file mark, which is why many buyers like it for finished jewelry, coins and bars.

XRF has real limits that a careful buyer keeps in mind. The reading describes the area being measured, down to a limited depth — not necessarily the whole object. Plating, coatings, surface dirt, the shape of the piece and the particular alloy can all affect how a result should be interpreted, so a thick gold layer over another metal may read very differently from the core underneath. And a composition reading on its own does not establish that a piece is authentic, where it came from, or whether it has collectible value.

For the jewelry evaluations we do every day, XRF gives a faster and more accurate composition reading than traditional acid testing. When a piece looks plated, hollow or altered, an experienced tester knows to take a closer look before settling on a result. Gold King uses XRF testing and acid testing to help evaluate precious-metal content and identify potentially counterfeit materials. The appropriate testing method depends on the item being evaluated. When acid testing is proposed as an alternative to XRF testing, customer approval is required.

• Visual hallmark and magnification check
• Magnet test to rule out base metals
• Acid test on a small scratch, by karat
• File test to check under plating
• Electronic tester reading
• XRF analysis of the measured area's composition
• Specific gravity (density) test on bullion or coins

XRF vs. electronic vs. acid testing

Here is how the three most common jewelry testing methods compare. The table describes each method in general terms so you know what you are seeing at any buyer's counter. At Gold King, XRF is our go-to because it is faster and more accurate than acid testing.

Specific gravity testing for coins and bars

For bullion coins and bars, where scratching or filing is undesirable, buyers often use a specific gravity test. The item is weighed dry, then weighed again submerged in water to work out its density. Gold is about 19.3 g/cm³, which separates it from many common base-metal fakes. Tungsten, however, has a density very close to gold's, so a tungsten-cored bar can pass a density check — one more reason this test is used as a cross-check alongside other methods rather than on its own.

No single test is perfect in isolation, which is exactly why a legitimate buyer layers several of them and chooses the methods that fit the item: a quick electronic or XRF reading on finished jewelry, a file and acid check where plating is suspected, density and dimension checks on bullion. If you only see one quick check happen before an offer is made, that is a reasonable moment to ask what else they plan to verify.

What you should watch a buyer do

You are entitled to watch every step of testing. A legitimate buyer will weigh your items on a visible, calibrated scale, explain which test they are running and why, and show you the result — whether that is an acid color change, an XRF readout, or an electronic tester reading. None of this should happen out of sight.

At our Southwest Freeway store in Houston, every test is performed at the counter in front of the customer, and we're happy to explain each step as we go. Stop by during store hours (Monday–Thursday 9:30 AM–7:00 PM, Friday–Saturday 9:30 AM–8:00 PM, Sunday 12:00–7:00 PM), or call 713-997-0875 with questions before you come in — testing and a free gold appraisal take only a few minutes. If you decide to sell, cash for gold at our Houston counter is paid during the same visit — by cash or another payment method — and broken pieces are welcome — see how scrap gold is weighed and valued.