PURIX
What do karat and fineness mean?
Karat writes the share of pure gold in an alloy out of 24; fineness writes it out of 1,000. They are two ways of writing the same ratio: 18 karat means 18 of 24 parts are gold, which corresponds to 750 fineness.1
| Karat | Fineness | Gold content | Where you see it |
|---|---|---|---|
| 24 karat | 999 and above | Pure gold | Gram gold, bars |
| 22 karat | 916 | 91.6% | Bangles, Turkish quarter gold coins |
| 18 karat | 750 | 75% | Diamond and designer jewellery |
| 14 karat | 585 | 58.5% | Everyday jewellery |
Touchstone
The piece is rubbed on a black stone, acid is dropped on the streak it leaves, and the colour of the streak is compared with samples of known karat. The result is a judgement made by eye, and a scratch is left on the piece. One test takes 1–2 minutes.
Acid test
Acid is applied directly to the surface of the piece and the reaction is observed. The result is not an exact number but a karat range (for example 14–18). It etches the surface; on plated pieces the information it gives is limited. One test takes 2–5 minutes.
XRF analysis
XRF sends X-rays into the piece. Each element emits rays at its own energy: gold at 9.71 keV, silver at 22.16 keV. The detector counts these rays and the software turns them into ratios.2
The three methods side by side
| Criterion | Touchstone | Acid test | XRF |
|---|---|---|---|
| Effect on the piece | Leaves a scratch | Etches the surface | None |
| Result | Karat by eye | Karat range (e.g. 14–18) | Percentage of all 20 elements |
| Time | 1–2 minutes | 2–5 minutes | 30–60 seconds |
| Plating detection | None | Limited | Reveals thin plating |
FAQ
Does XRF measurement damage the piece?
No. There is no cutting, scraping or acid; the piece stays exactly as it was before the measurement.
What does a 916 stamp mean?
It shows that 916 of every thousand parts are pure gold; this corresponds to 22 karat.
How long does one measurement take?
With the PURIX X1, 30–60 seconds per piece.
All values are measured under the manufacturer’s test conditions and may vary with the shape and surface of the sample.
Karat isn’t guessed. It’s measured.
Try the live analysis to see how a measurement looks on screen, or request a quote for your business.