Gold Acid Test Colors Explained | Karat-by-Karat Guide
Share
You've applied the acid. Now what? Understanding gold acid test colors is what separates a confident result from a confusing smear on a testing stone. This guide explains exactly what happens when acid meets real gold versus fake gold, and walks you through every karat level so you know what you are looking at.
Skip the guesswork — test any karat in seconds.
Shop the TrueAssay Gold Testing Kit →Labeled solutions for 10K–22K • Trusted by jewelers & pawn shops • Ships in 24 hours
Safety first: Always use acid testing solutions with gloves, eye protection, and good ventilation. These are strong acids that can cause burns and irritation.
Ready to test your own pieces? Shop the TrueAssay gold testing kits — a labeled solution for every karat, delivered in one box.
What Happens When Acid Touches Gold
The chemistry behind acid testing is straightforward. Testing acids are nitric acid solutions calibrated to specific concentrations. Gold is one of the least reactive metals on earth — it resists acids that dissolve most other metals. The higher the karat (meaning the higher the percentage of pure gold), the more resistant the piece will be.
When you apply acid to a gold mark on a testing stone, one of three things happens:
- No reaction — The mark stays intact. The piece is genuine gold at or above the tested karat.
- Partial reaction — The mark fades slowly over 20–30 seconds but doesn't fully disappear. This means gold is present, but at a lower karat than the acid you used. A slow, gradual fade is normal for pieces that are slightly under-karat. Instant disappearance means the piece is well below the tested level or not gold.
- Full dissolution or discoloration — the mark disappears or turns a dark color quickly. The piece is below the tested karat, plated, or not gold at all.
Karat-by-Karat Color Guide
- 9K / 10K: Genuine 10K gold will hold up or show only a faint cream/tan reaction under 10K acid.
- 14K: Holds largely intact against 14K acid; shows mild fading under 18K acid.
- 18K: Holds firm against 18K acid; reacts and fades under 22K acid.
- 22K: Holds firmly against 22K acid.
Reading these reactions correctly is far easier when your acid is calibrated to each karat. The TrueAssay 9K–22K Acid Test Kit includes a separate, clearly labeled solution for every karat level above — so you're never guessing which acid to use or second-guessing a result. Shop the karat test kits →
Testing Tips for Accurate Results
- Lighting: Test in bright, natural light to distinguish color nuances.
- Reference: Scratch a known gold reference needle alongside the sample.
- Persistence: Wait the full 20–30 seconds — reactions can be gradual.
- Contamination: Clean the testing stone with water between tests.
- Plated items: Plating often reacts strongly (dark green/brown) once the acid penetrates the surface to hit the base metal.
Ready to Test With Confidence?
Get lab-grade acids and complete kits trusted by jewelers, refiners, and pawn shops worldwide. Every solution is calibrated for accurate, repeatable karat readings.
- 👉 Shop All Gold Testing Kits — everything you need in one box.
- 👉 Shop Individual Testing Solutions — restock a single karat.
New customer? Use code NITRIC10 at checkout for 10% off your first kit.
Keep learning: