Is that jewelry real gold? Here's how to actually find out.

You found some old jewelry in a box and you have no idea if it's real. Maybe it came from an estate, maybe you bought it at a flea market years ago, maybe you just never thought to check. Either way, you want to know before you bring it somewhere.

Here's how to figure it out.

Start with the stamps

This is step one. Most gold jewelry made in the US has a purity stamp somewhere on it. Look for it on the clasp of a necklace, the inside of a ring band, or the back of a pendant.

Common marks you'll see:

• 10K, 14K, 18K, 24K — the K stands for karat, which measures how much of the metal is actually gold
• 417, 585, 750, 999 — these are European hallmarks for the same karats (417 = 10K, 585 = 14K, 750 = 18K, 999 = 24K)
• GF — gold-filled. Not solid gold. Much less value.
• GP — gold-plated. Also not solid gold. Even less value.
• No stamp at all — doesn't mean it's fake. Older pieces, especially antiques from before the 1900s, often weren't stamped.

If you see GF or GP, set that piece aside. Gold-filled and gold-plated jewelry have a thin layer of gold over a base metal. You're not going to get meaningful money for them, because there's almost no actual gold there.

A 14K stamp, on the other hand, means 58.5% of that piece is solid gold. At today's prices (gold is around $5,092 an ounce right now), even a small 14K ring can be worth $100-$400 depending on weight.

The magnet test

Gold is not magnetic. Grab a strong magnet (a rare earth magnet works much better than a fridge magnet for this) and hold it close to the piece.

If the piece gets pulled toward the magnet, you've got a problem. It's either not gold, or it has a base metal core with a gold coating.

If nothing happens, that's a good sign. It doesn't prove the piece is gold, but it rules out the most common cheap fakes, which are usually iron or nickel underneath.

The acid test

This is what professional buyers use, and it's the most reliable method short of electronic testing.

You can buy a gold acid test kit for about $20 at most jewelry supply stores or on Amazon. The process is straightforward: scratch the piece lightly against a black testing stone, then apply a drop of acid to the scratch. Real gold resists the acid. Fake metals or base metals under a gold coating will discolor or dissolve pretty quickly.

Different acid concentrations test for different karats. The kit will tell you which acid to use for 10K vs 14K vs 18K testing.

One honest caveat: this test is fussy. If you do it wrong, you can get a misleading result or damage the piece. For anything you think might be valuable, skip the kit and just bring it to a buyer who tests for free. No reason to risk it.

The ceramic streak test

Drag the piece across the back of an unglazed ceramic tile, like the rough unfinished bottom of a coffee mug. Real gold leaves a gold-colored streak. Pyrite (fool's gold) leaves a black or dark streak.

This test is reliable for coins and nuggets but less practical for jewelry, since the scratching can leave a visible mark. Use it as a quick check, not a primary test.

What about the skin test?

You've probably heard this one: if your skin turns green where the jewelry touches it, the piece is fake. It's not quite that simple.

Real gold doesn't react with skin. If a piece is turning your skin green, it either has copper or nickel mixed in, which is common in lower-karat gold (10K has more copper than 14K), or it isn't gold at all.

The problem is that sweat, lotions, and humidity can all affect whether you get a reaction. It's too unreliable to use as a deciding factor. Take it as a warning sign, not a verdict.

Two tests worth skipping

The float test: some sites claim real gold sinks in water and fake gold floats. Gold is dense and does sink. But so do plenty of other metals. And hollow gold pieces can float. This test tells you almost nothing.

The bite test: pure gold is soft enough to show teeth marks, which is why Olympic medals are often bitten for photos. But lead is also soft. You're not testing for lead. And you might leave visible damage on something worth a few hundred dollars. Just skip it.

When home tests aren't enough

If you've got a piece with karat stamps and it passed the magnet test, you probably have real gold. But home tests can't tell you how much it's worth, and they can't give you an accurate karat reading.

For that, you need a buyer with a proper testing setup.

At Cash 4 Gold Trading Post, we use both acid testing and an electronic analyzer. The electronic tester is non-destructive and gives a precise karat reading in about 30 seconds. We weigh everything on a calibrated scale. The whole process takes maybe 10-15 minutes for a typical collection. No charge, no commitment to sell anything.

If you have a drawer full of old jewelry and you're not sure what's real, bring it all. We'll sort through it, tell you what's gold, what's silver, what's plated, and what's costume. You get to watch the testing. You decide what to do with the information.

Quick reference: what the stamps mean

Come in any time

Cash 4 Gold Trading Post has 6 locations across Central New Jersey. Walk in Monday through Saturday, no appointment needed.

• East Brunswick: (732) 898-6565
• New Brunswick: (732) 543-1313
• Middlesex: (732) 629-7600
• Millstone: (732) 444-2022
• Brick: (732) 444-2094
• Manalapan: (732) 444-2022

Bring whatever you have, tested or untested. We'll tell you exactly what it's worth.