You don't need a gemology degree to know a good diamond when you see one. In fact, there are simple, practical things you can look for — and watch out for — that will immediately tell you whether a diamond is worth the price tag.
Here's what the pros look for, explained in plain English.
Look at the Light Performance
The single most important indicator of diamond quality is how it handles light. A well-cut diamond will show three things: brightness (white light reflecting back), fire (flashes of rainbow color), and scintillation (sparkle as the diamond moves).
Hold the diamond face-up under a standard overhead light and tilt it gently. A quality diamond will flash brightly with every movement. A poorly cut diamond will look dark or glassy in certain angles. Trust your eyes on this one — you can see the difference immediately.
The "Tilt Test" for Cut Quality
Place the diamond on a flat surface with the table (top face) facing up. Tilt it slowly. A well-cut diamond will show a crisp, symmetrical pattern of light and dark. An excellent cut will show eight perfect arrows from the top. A poorly cut diamond will look lopsided, with light leaking out from the sides.
This test works for round brilliant cuts. For fancy shapes (oval, pear, emerald), look for even brightness across the entire surface without dark spots or shadowed areas.
Read the Certification
Never buy a diamond without an independent certification from GIA, IGI, or AGS. These reports tell you exactly what you're getting. Look for the cut grade first (Excellent or Ideal for maximum sparkle). Then check that the symmetry and polish grades are also Excellent or Very Good.
If a seller offers their own "in-house certification" instead of an independent one, proceed with extreme caution. It's not necessarily a red flag, but it means the grading standards may not be consistent with the rest of the industry.
Check for Inclusions You Can See
Look at the diamond with your naked eye from about 8 inches away. Can you see any dark spots, white flecks, or feather-like marks? If yes, that's an inclusion that affects the clarity grade. Most SI1 and SI2 diamonds are "eye-clean" — meaning you can't see inclusions without magnification. But some aren't. Always verify with your own eyes.
The best place to check is through the side of the diamond (the pavilion), looking up toward the table. Inclusions are often visible here first.
The "Breath Test" for Authenticity
This is a quick trick to differentiate diamond from moissanite or cubic zirconia. Breathe on the stone to fog it up. A real diamond disperses heat instantly — the fog will clear in 1-2 seconds. Moissanite takes 3-5 seconds. Cubic zirconia takes even longer.
This isn't a definitive test (some lab-grown synthetics behave similarly), but it's a useful first check. For absolute certainty, ask for a thermal conductivity test or diamond tester.
Check the Girdle
The girdle is the outer edge where the crown (top) meets the pavilion (bottom). Run your fingernail along it gently. An extremely thin girdle can chip during setting. An extremely thick girdle means the diamond was cut to preserve weight rather than beauty — and that weight doesn't contribute to visual size.
A well-proportioned diamond has a girdle rated "thin to slightly thick" on the certification. If it says "very thick" or "extremely thick," you're paying for hidden weight that doesn't add sparkle.
Trust the Seller, Not Just the Stone
Even the best diamond can be misrepresented. Buy from a seller with transparent policies, clear return windows, and a reputation for honesty. At Lara Jewels, every diamond is independently certified, and our team will walk you through every characteristic with complete transparency.
A quality diamond comes from a quality seller. When you find both, you've found something truly valuable.
