How to Read Gold Acid Test Results: What the Dissolving Line Actually Means (2026 Guide)
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You scratched your gold on the stone, dripped on the acid, and watched something happen—but what does it actually mean? This is the single most common point of confusion for new testers, and getting it backwards can cost you real money on a buy. Here's exactly how to read your gold acid test results the way pros do.
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Shop the 9K–22K Gold & Platinum Kit →Quick Answer (TL;DR)
- Line stays put = the gold is that karat or higher. That's a pass.
- Line dissolves or fizzes away = the gold is below that karat (or not real gold). That's a fail.
- Start with your lowest acid and work up. The last acid the line survives is your karat.
- Always file through plating first, and clean the stone between every test.
The One Rule That Confuses Everyone
Gold acid testing works by elimination, not confirmation. Each bottle is calibrated to a karat value (10K, 14K, 18K, 22K). When you apply an acid to your scratch line, you are asking one question: "Is this gold at least as pure as the number on the bottle?"
Remember it this way: a dissolving line is a failed test, not a passing one. If your 18K acid erases the line, the piece is not 18K.
Gold Acid Test Results at a Glance
| What You See | What It Means |
|---|---|
| No reaction — line stays | Gold is at or above that acid's karat |
| Slow brown fade | Real gold, but slightly below that karat |
| Line dissolves quickly | Below that karat |
| Green, bubbling / effervescent | Base metal or gold-plated |
| Milky / cream / white | Gold-plated sterling silver |
Step-by-Step: How to Read the Reaction
- File through any plating first. Testing a plated surface gives a false "pass." Expose fresh metal before you scratch.
- Make a solid, visible line on your testing stone.
- Start low, work up. Begin with 10K acid. If the line survives, move to 14K, then 18K, then 22K.
- Watch for 20–40 seconds. When the line finally dissolves, the previous karat is the piece's value.
- Neutralize and clean the stone with baking soda and water before the next test.
New to the process? Start with our complete guide to testing gold at home, or see the full karat-by-karat color chart.
"Why Won't My Acid React on 22K or 24K Gold?"
This trips up a lot of resellers. The purer the gold, the stronger the acid needed to dissolve it. Standard testing acids do very little to gold above roughly 22K, and 24K resists nearly everything short of aqua regia. So if your highest acid leaves the line untouched, that's not a broken kit—it's a strong signal you're holding very high-purity gold. Confirm with a scale/density check or an electronic tester for the final word.
Common Reasons Your Results Look Wrong
- You tested over plating. Always file down to bare metal.
- Cross-contaminated stone. Old acid residue skews new tests—clean between every reading.
- Expired acid. Write the open date on each bottle; potency drops over time.
- Tested a solder joint or clasp. These are often a different alloy than the body of the piece. On chains, test several links.
- Too little metal on the stone. A faint line disappears fast and reads as a false fail.
Seeing results that don't add up? Our guide on why your acid test results look wrong covers the sneakiest culprits.
Safety First
Testing acids are corrosive. Wear gloves and eye protection, work in a ventilated area, keep bottles tightly capped, and keep a baking-soda-and-water neutralizer within reach. Never test collectible coins, and always dilute heavily when disposing of neutralized residue.
Frequently Asked Questions
Does the line staying mean the test passed?
Yes. If the scratch line survives the acid, the gold is that karat or purer. A line that dissolves means it falls short.
Which acid should I start with?
Always start with your lowest karat acid (usually 10K) and work upward. This avoids destroying the line before you find the true value.
Why is there no reaction at all?
Either the gold is at or above that acid's karat, or you're testing very high-purity gold (22K–24K) that standard acids can't dissolve. Move up a karat or confirm with density/electronic testing.
Can acid testing damage my jewelry?
The scratch and acid are applied to a tiny, discreet spot. Choose an inconspicuous area, and neutralize promptly to minimize any mark.
The Bottom Line
Reading a gold acid test comes down to one habit: watch whether the line survives. A surviving line means the gold meets or beats that karat; a dissolving line means it falls short. Start low, climb up, and let the last surviving acid tell you the answer.
Get Accurate Results Every Time
Stop second-guessing your buys. The TrueAssay Gold & Silver Testing Kit comes with clearly labeled 10K, 14K, 18K, and 22K acids, a professional testing stone, and neutralizer—everything you need to read results with confidence.
→ Shop TrueAssay testing kits | Questions? Talk to our team