What are the most common fake diamonds?
The usual diamond look-alikes are cubic zirconia, moissanite, white sapphire, glass and, in older jewellery, synthetic spinel, YAG and GGG. Cubic zirconia is the most common. None is diamond: each differs in hardness, weight, fire and how it reacts to a tester, so a jeweller can tell them apart quickly.
How to Tell if Your Diamond is Real
Professional methods to identify authentic diamonds and avoid costly mistakes when buying or selling diamond jewellery
Faustas Svencionis
Managing Director, Mozeris Fine Antiques
Diamonds represent significant financial investments and emotional value, particularly in engagement rings and heirloom jewellery. With the increasing prevalence of synthetic diamonds and diamond simulants in the market, understanding how to verify diamond authenticity has become essential for both buyers and sellers.
Multiple diamonds set in gold require individual verification for authenticity
Professional Diamond Authentication Methods
- Certificate of Authenticity: Reputable jewellers provide certificates from recognised gemological laboratories such as GIA (Gemological Institute of America), SSEF, or Gübelin. These certificates verify natural origin and provide detailed specifications including carat weight, cut grade, clarity, and colour grading.
- Hallmark Verification: Authentic diamond jewellery typically features hallmarks engraved on the metal setting. Look for stamps indicating gold purity (9ct, 14ct, 18ct) or platinum marks (PLAT, PT950). GIA-certified diamonds may have laser inscriptions on the girdle.
- Fog Test Analysis: This simple test exploits diamonds' superior thermal conductivity. Breathe directly onto the stone's surface - genuine diamonds dissipate heat rapidly and remain clear, while simulants retain fog for several seconds.
- Inclusion Examination: Natural diamonds contain unique internal characteristics called inclusions - tiny crystals, feathers, or clouds formed during the diamond's creation process. These inclusions serve as fingerprints for authentication.
- Professional Loupe Inspection: A 10x magnification loupe reveals crucial details about cut quality, facet alignment, and surface characteristics. Examine the girdle for laser inscriptions and assess the overall craftsmanship.
Professional diamond cutting creates precise facets that reflect light distinctively
Understanding Diamond Simulants and Synthetics
Diamond simulants include cubic zirconia, moissanite, and white sapphire - materials that resemble diamonds but possess different chemical compositions. Laboratory-grown diamonds, however, share identical chemical properties with natural diamonds, making identification significantly more challenging without professional equipment.
Fancy coloured diamonds require specialised authentication due to their rarity
Advanced Testing Methods
Professional gemologists employ sophisticated instruments including diamond testers, which measure thermal conductivity, and spectroscopy equipment that analyses light absorption patterns. These tools can distinguish between natural diamonds, synthetics, and simulants with high accuracy.
Antique Victorian jewellery requires expert evaluation due to historical cutting techniques
Red Flags to Avoid
Be cautious of sellers who cannot provide certification, offer prices significantly below market value, or refuse professional inspection. Genuine diamond dealers welcome third-party verification and provide comprehensive documentation.
Mixed gemstone pieces require individual stone verification
Latest, 8 October 2026: the ring that was not glass
A clip from the BBC's Antiques Roadshow, filmed at Cardiff Castle in 2017, was in the news again this week. A visitor brought a ring her grandmother had given her as a teenager, believing its large pink centre stone was glass. The programme's jewellery specialist, John Benjamin, identified it as a pink tourmaline of about 12 to 13 carats in a diamond surround, with sapphires and diamonds on the shoulders, made in the Art Deco style around 1925 to 1930.
The checks in this guide work for coloured stones too. Start with the setting and the metal marks, then look at the stone under a 10x loupe. Glass is softer than most gemstones, so its facet edges often look rounded or chipped, and it can show round gas bubbles inside. Not sure about a family ring? Send us a few photos and we will tell you what it is, free and with no obligation.
Sources: Express via AOL, 7 October 2026; GIA Gems & Gemology lab notes
Frequently Asked Questions
What is the most reliable way to verify if a diamond is real?
The most reliable method is obtaining a certificate of authenticity from a reputable gemological laboratory such as GIA, which provides detailed analysis of the diamond's characteristics and confirms its natural origin.
Does the fog test work for identifying real diamonds?
Yes, the fog test can be helpful. Real diamonds dissipate heat quickly and won't fog up when you breathe on them, while fake diamonds will remain fogged for several seconds due to slower heat dissipation.
Can synthetic diamonds be distinguished from natural diamonds?
High-quality synthetic diamonds can be very difficult to distinguish from natural diamonds without professional equipment. This is why certification from reputable laboratories is essential for verification.
What is cubic zirconia?
Cubic zirconia, or CZ, is a man-made crystal of zirconium dioxide, mass-produced for jewellery since the late 1970s. It is about 8 to 8.5 on the Mohs scale, much heavier than diamond and more fiery, and its edges wear and its surface dulls with years of wear. It is the most common diamond simulant.
Is moissanite better than cubic zirconia?
They are different stones. Moissanite is harder, about 9.25 on the Mohs scale against 8 to 8.5 for cubic zirconia, so it keeps its polish and sharp edges longer, and it stays bright with wear. Cubic zirconia is heavier and scratches and clouds more over time. Neither is diamond.
Is moissanite a real diamond?
No. Moissanite is silicon carbide, a different material from diamond, which is carbon. It is a real gemstone and is sold honestly as moissanite, but it is not diamond. It is doubly refractive, so its back facet edges look doubled through a loupe, and it shows stronger rainbow fire than diamond.
How does a diamond tester work?
A standard diamond tester measures how fast the stone conducts heat. Diamond carries heat away very quickly, so it reads as diamond while glass and cubic zirconia do not. A multi tester also measures electrical conductivity, which separates moissanite. Neither type separates lab-grown from natural diamond.
Does moissanite pass a diamond tester?
Moissanite passes a basic thermal diamond tester, because it conducts heat almost as well as diamond; GIA reported this when moissanite first appeared in 1997. A multi tester that also checks electrical conductivity identifies it, and a loupe shows its doubled facet edges. Any moissanite can fool a thermal tester.
Are lab-grown diamonds real diamonds?
Yes. A lab-grown diamond is made of carbon with the same crystal structure as a mined diamond, so it is chemically, physically and optically diamond. It is not a simulant. It must be sold as laboratory-grown, and a gem laboratory report states whether a diamond is natural or laboratory-grown.
Are lab-grown diamonds the same as cubic zirconia?
No. A lab-grown diamond is real diamond, 10 on the Mohs scale, with diamond's weight and brilliance. Cubic zirconia is a different material, softer at about 8 to 8.5, heavier, and more fiery. A diamond tester reads a lab-grown diamond as diamond and cubic zirconia as not diamond.
Can a diamond tester detect a lab-grown diamond?
No. A lab-grown diamond conducts heat like any diamond, so a standard tester reads it as diamond. Separating lab-grown from natural needs laboratory instruments that look at growth patterns, fluorescence and trace elements. GIA and other laboratories issue reports that state natural or laboratory-grown.
Do lab-grown diamonds sparkle like natural diamonds?
Yes. Lab-grown and natural diamonds have the same refractive index and dispersion, so two stones of the same cut, colour and clarity sparkle the same way and cannot be told apart by eye. How much a diamond sparkles depends on its cut, not on whether it was mined or grown.
What is a trillion cut diamond?
A trillion cut is a triangular diamond with three equal sides, often with slightly curved edges, cut as a brilliant to give strong sparkle. It is used as a solitaire and, more often, as a pair of side stones beside a centre diamond. Its thin corners need protective claws or a bezel setting.
Can an Art Deco style ring have cubic zirconia?
Only if it is a modern ring or a stone has been replaced. Cubic zirconia was not made for jewellery until the late 1970s, so a ring made in the 1920s or 1930s was set with diamonds, synthetic spinel, paste or other stones of its time. Many modern rings copy the Art Deco style with cubic zirconia.
Vintage diamond pieces showcase historical cutting and setting techniques
Professional Evaluation Services
When purchasing significant diamond jewellery or inheriting family pieces, professional evaluation provides peace of mind and accurate valuation. Qualified gemologists can identify treatments, assess quality grades, and provide insurance documentation.
For Art Deco jewellery and Edwardian pieces, understanding period-specific diamond cutting techniques becomes crucial for accurate authentication and valuation.
Need Professional Diamond Authentication?
Our certified gemologists provide comprehensive diamond evaluation services with detailed reports and insurance valuations.
Related Diamond Services
Whether you're examining diamond necklaces, diamond earrings, or diamond bracelets, these authentication methods apply universally across all diamond jewellery categories.
Conclusion: Authenticating diamonds requires combining multiple verification methods. While simple tests like the fog test provide initial indicators, professional certification remains the gold standard for diamond authentication. When in doubt, consult qualified gemologists who possess the expertise and equipment necessary for accurate identification.
For valuable pieces or significant purchases, the cost of professional evaluation represents a small investment compared to the potential financial loss from purchasing treated, synthetic, or simulated diamonds unknowingly. Whether dealing with Georgian jewellery or contemporary pieces, proper authentication protects your investment.
Moissanite fools a basic thermal tester, so see moissanite vs diamond for the checks that separate them. A standard tester reads lab-grown stones as diamond too: read lab-grown vs natural diamonds.
Thinking of selling? Find out how to sell a diamond ring with a free valuation from photographs.
