How to Spot a Fake Diamond: Tests and Their Limits

The internet is full of tricks for testing diamonds at home. Some have a grain of truth, but none is dependable for a purchase. Knowing how imitations differ, and what a proper check involves, will protect you better than any trick.

What counts as fake?

• Simulants: materials that look like diamond but are not, such as cubic zirconia, glass or white sapphire.
• Moissanite: a different gemstone, very similar to diamond in appearance, which is sometimes sold as a diamond alternative.
• Treated or enhanced diamonds: real diamonds that have had their clarity or colour modified. These should be disclosed.
• Laboratory-grown diamonds: real diamonds, chemically the same as natural ones, made in a laboratory. They must be disclosed as such. See lab-grown diamond jewellery: questions to ask.

Home tests and their limits

• The fog test: breathe on the stone. Diamond disperses heat so quickly that fog clears fast. But some imitations and a clean stone can behave similarly, and a dirty stone holds fog.
• The newspaper test: place the stone over print and see if you can read through it. A well-cut diamond bends light so you cannot, but some imitations behave similarly.
• The water test: diamonds are dense and sink in water. Many imitations also sink.
• The scratch test: hardness is real, but scratching a stone risks damage and proves little.
• The UV test: many diamonds fluoresce, but many do not, and other stones do too.

None of these separates diamond from every alternative.

What a jeweller can do

• Examine under a loupe: natural diamonds have characteristic inclusions and sharp, crisp facet edges. Simulants often show rounded edges, bubbles or different internal features.
• Use a thermal tester: a pen-like device measures how quickly heat moves through a stone. It separates diamond from many imitations, though some testers are fooled by moissanite unless they are designed to detect it.
• Use an electrical conductivity test: helps to distinguish moissanite.

What a laboratory can do

A gemological laboratory uses spectroscopy and other equipment to identify a stone, tell natural from laboratory-grown and detect treatments. This is how a certificate is produced. See what diamond grading labs actually do.

The practical protection

1. Buy from a reputable seller who is transparent about what you are buying.
2. Ask for a certificate from an established laboratory for any significant stone.
3. Check the report number online and look for the laser inscription on the stone.
4. Look at the invoice: it should describe the stone as natural or laboratory-grown, with its grades.

Warning signs

• A price far below comparable stones.
• No report for a stone that is described as a high grade.
• Reluctance to let you inspect the stone under magnification.

What about diamonds in jewellery?

Small stones in jewellery are not certified one by one. The honesty of the seller and the description on the bill matter. See melee diamonds.

If you already own a stone you doubt

Do not test it with force or acid. Take it to a jeweller who can examine it under magnification and with a thermal tester, and, if the answer matters, to a gemological laboratory for identification. For inherited stones, an identification report is worth its modest cost, because it settles the question for good and gives you a document to keep.

See stones with documents

Our certified diamond jewellery comes with the details to match. Book an appointment to see stones under magnification, or look at the details on our diamond pendants.