A fake diamond can be spotted using simple at-home checks like the fog test, scratch resistance and refractivity, but the most reliable method is to have it examined by a professional jeweller or use an electronic diamond tester. Fake stones such as cubic zirconia or moissanite often have different weight and sparkle characteristics than real diamonds.
Quick at-home checks
- Fog test – Breathe on the stone; real diamonds disperse heat quickly so the fog clears almost instantly, while fake stones stay fogged for longer.
- Scratch resistance – Diamonds are the hardest natural material (Mohs 10); simulants like glass may show surface scratches and wear. Be cautious: do not damage the setting.
- Refractivity – Real diamonds sparkle sharply with white light and flashes of colour (fire); fakes may show more rainbow colours or lack brilliance.
- Loose newspaper test – Place the stone table-down on a newspaper; if you can read the print through it, it may not be a diamond because diamonds refract light strongly.
Professional testing tools
- Diamond testers – These handheld devices measure thermal or electrical conductivity; real diamonds have high conductivity compared with simulants.
- Microscope examination – Jewellers examine facet edges, inclusions and girdle to tell natural diamonds from simulants.
- UV fluorescence – Many diamonds fluoresce under UV light; pattern and intensity differences can help identify simulants.
Caveats
Lab-grown diamonds have the same physical properties as natural ones and will pass most tests, so only a gemmologist can verify origin. Some high-quality simulants may mimic a diamond's thermal properties.
Frequently asked questions
- Can I test diamonds with water? Water tests (like dropping the stone into water to see if it sinks) are unreliable; density differences among simulants are small.
- Are lab-grown diamonds “fake”? No. Lab-grown diamonds have the same physical and optical properties as mined diamonds; they are real diamonds, just created in a lab.
- Should I buy a diamond tester? A tester can offer peace of mind, but professional testing is more accurate and includes additional checks.
Last updated: March 2026