A diamond is often at the centre of the jewellery that means most: an engagement ring, an anniversary gift, a ring handed down through the family. When a piece like that has no paperwork, or you have simply never been sure what you were given, it is natural to want to know what the stone really is.
You can’t reliably tell by eye, and most of the tests people try at home can mislead. A trained jeweller uses a loupe and an electronic tester, and a grading report or a valuation settles it. If you are choosing a diamond rather than checking one, start with our guide to how to choose a diamond.
A lab-grown diamond is a real diamond, with the same chemical composition and crystal structure as a natural one, so it passes every test below. These tests tell you whether a stone is diamond, not where it came from; we explain that difference in lab-grown or natural diamonds.
At Anupam, our engagement rings are set with natural or lab-grown diamonds, and the centre stones are certified by IGI or GIA. This article covers the home tests you may have read about, what to check on the ring itself, and what a jeweller actually does.
Can you look at a diamond and tell if it’s real?
Not reliably. The stones most often mistaken for diamond are cubic zirconia, moissanite, white sapphire, white topaz and glass, and a good look-alike can fool the eye.
The give-aways are subtle:
- more rainbow colour in the sparkle than you would expect;
- a stone that looks too perfect;
- a setting that doesn’t match the quality of the stone it holds.
Which home tests are worth trying, and which mislead?
Most of the advice online is half right, which is the problem. Here is what each test claims, and why it can’t settle the question.
| Test | What people say | Why it can’t be trusted |
|---|---|---|
| Fog test | Breathe on the stone. A diamond clears almost at once. | Moissanite clears quickly too, and a diamond with oil or dirt on it stays fogged. |
| Water test | A diamond sinks in a glass of water. | So do cubic zirconia, glass and most other stones. It proves nothing. |
| Newspaper test | Put the stone face down on print. If you can read through it, it isn’t a diamond. | It needs a loose, well-cut stone, and several look-alikes pass it too. |
| Sparkle test | A diamond flashes white and grey, while look-alikes flash rainbow colours. | Look-alikes often do show more colour, but a dirty diamond looks dull and lighting changes everything. |
| UV light test | A diamond glows blue under ultraviolet light. | Many diamonds don’t glow at all, and some look-alikes do. |
| Scratch test | A diamond scratches glass. | Sapphire and moissanite do too, and you risk marking the ring or chipping the stone. |
Our advice: the fog, water, newspaper, sparkle and UV tests are safe to try if you only want a rough idea. Don’t try the scratch test, and never hit a stone with a hammer. Diamond is the hardest naturally occurring mineral, but hard isn’t the same as tough, and a sharp knock can chip it.
What can you check on the ring itself?
The hallmark
Look at the metal first. A ring sold in the UK as 9ct, 14ct or 18ct gold, or as platinum 950, must be hallmarked unless it falls under the exemption weight: 1g for gold and 0.5g for platinum. The hallmark has three compulsory parts: the sponsor’s mark, showing who submitted the piece for hallmarking; a number for the fineness; and the assay office mark.
- 375 means 9ct gold.
- 585 means 14ct gold.
- 750 means 18ct gold.
- 950 means platinum 950.
A hallmark tells you about the metal, not the stone, so it doesn’t prove the diamond is real. A stamp such as “CZ” inside the band, however, tells you the stone is cubic zirconia. UK hallmarks explained shows how to read the marks.
The paperwork
A diamond bought with a grading report describes itself, and many have the report number laser-inscribed on the edge of the stone, which a jeweller can match to the paper under magnification. A report from a laboratory such as GIA or IGI also states whether the diamond is natural or lab-grown.
If you have a certificate, a receipt or an earlier valuation, keep it with the ring.
What does a jeweller actually check?
- A loupe, at ten times magnification. Most diamonds have tiny marks inside and sharp, straight edges where the facets meet. Cubic zirconia is softer, so its facet edges often look rounded and worn. Moissanite shows a doubling of the back facets when you look through the stone at an angle, because it splits light in two.
- An electronic tester. It measures how quickly a stone conducts heat and, in better testers, electricity. Diamond and moissanite both conduct heat well, so a heat-only tester can mistake moissanite for diamond. A tester that also checks electrical conductivity can tell them apart.
- Weight against size. Cubic zirconia is much denser than diamond, so a loose cubic zirconia stone weighs considerably more than a diamond of the same size.
Here is how a diamond compares with the two look-alikes most often confused with it.
| Check | Diamond, natural or lab-grown | Moissanite | Cubic zirconia |
|---|---|---|---|
| What it is | Carbon, with diamond’s crystal structure | A separate gemstone made from silicon carbide | Another diamond alternative, popular in fashion jewellery |
| Hardness (Mohs scale) | 10 | About 9.25 | About 8–8.5 |
| Under a loupe | Sharp, straight facet edges | Back facets look doubled at an angle | Facet edges often look rounded and worn |
| Heat-only tester | Reads as diamond | Can also read as diamond | Doesn’t read as diamond |
Should you get the stone valued?
If your ring came with a grading report from a jeweller you trust, you already have your answer. If not, a valuation is the clearest way to find out.
An insurance valuation records in writing what the stone is and what the ring is made of, and puts a figure on it: the cost of replacing it with a comparable piece, which is what engagement ring insurance asks for.
At Anupam, we arrange independent insurance valuations with Shirley Mitchell FGA DGA FJVA, and jewellery valuations explained sets out the fees.
If the ring is an inheritance, what to do with inherited jewellery may help with what comes next.
Have a stone looked at in Ashford
If you would like a stone looked at, or want to talk through a valuation, book a time with us in Ashford, and bring any certificates, receipts or earlier valuations you have. We’re always happy to have a conversation about a stone, but testing it isn’t a free service, because it takes time and the use of our equipment.
If you are looking for a diamond of your own, you can browse our engagement rings.
Frequently asked questions
What is a “poor man’s diamond”?
It is an informal name given to diamond look-alikes such as cubic zirconia, moissanite or white sapphire. Each is a different gemstone with its own hardness and sparkle, rather than a lesser kind of diamond. We use cubic zirconia, for example, for the coloured birthstone-style stones in our sterling silver birthstone pendants, and describe them as cubic zirconia.
Do real diamonds sparkle with rainbow colours?
Yes, to a degree. A diamond shows bright white light with flashes of colour, often called fire, and how much depends on its cut. Moissanite tends to show more pronounced rainbow flashes, which is why the difference can be easier to see in strong sunlight.
How are diamonds graded?
By the 4Cs: cut, colour, clarity and carat. Colour is commonly graded on a D–Z scale, and a report from a laboratory such as GIA or IGI records each grade. How to choose a diamond explains what each one means for how a stone looks.
How much is a 1 carat diamond worth?
There is no single figure. It depends on the cut, colour and clarity, and on whether the diamond is natural or lab-grown, with lab-grown diamonds generally less expensive than a comparable natural one.
Can a real diamond chip or scratch?
It can chip. Very little will scratch a diamond, but diamonds can scratch one another. That is why diamond jewellery is best stored apart, and our guide to looking after your jewellery explains how.
