Gold purity and testing
Karat to fineness for gold, the legal fineness marks for silver, platinum and palladium, and how the common test methods work.
Gold karat and fineness
Karat counts gold in 24 parts. Fineness counts it in 1,000 parts, so 750 means 750 parts gold per 1,000.
| Karat | Gold content | Fineness mark |
|---|---|---|
| 9K | 37.5% | 375 |
| 10K | 41.7% | 417 |
| 14K | 58.3% | 585 (583) |
| 18K | 75.0% | 750 |
| 20K | 83.3% | 833 |
| 22K | 91.7% | 916 |
| 24K | 99.9%+ | 999 |
Other precious metal standards
- Silver
- 800, 925, 958, 999
- Platinum
- 850, 900, 950, 999
- Palladium
- 500, 950, 999
Fineness standards recognized in hallmarking law. Sterling silver is 925 and most platinum jewelry is 950.
Why 14K is stamped 585
Strictly, 14 of 24 parts is 58.3% (583). Most makers alloy 14K slightly over that and stamp it 585, following European practice. A stamp states the claimed fineness, not a test result.
Test methods
Test anything with no stamp, a doubtful stamp, or a value that matters, like scrap buying.
| Method | How it works |
|---|---|
| Touchstone and acid | Rub the piece on a black test stone to leave a streak, lay streaks of known karat needles beside it, and apply acid. Purer gold resists stronger acid. Measured nitric acid solutions test 14K and lower, and aqua regia tests higher karats. Compare which streaks remain. |
| Electronic tester | Measures the metal's electrical response at a probe and reads out a karat range. It's fast and leaves no streak, but it reads only the surface. |
| XRF analyzer | X-ray fluorescence reads the full alloy composition without marking the piece. It's the most precise bench method, but it still reads only near the surface. |
Watch for plating
Gold-plated and gold-filled items can pass a surface test. For acid testing, take the streak from an inconspicuous spot, or file a small notch to test below the surface. Handle acids with gloves and eye protection, and neutralize spills.
Scales and testers
All scales and testers-
3-Piece Gold Test Needle Set (10K, 14K, 18K)
$45.95 -
ASTRO Two-Way Colorstone Referential Meter
$379.00 -
AuRACLE ANALYZER
$375.00 -
Belize Pro and Astro Bundle
$1,599.00
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