"I've looked at hundreds of diamonds a day for more than twenty years, and I can usually tell in a few seconds whether a stone is real."
That's Hemant, who leads The New York Tour of Diamonds on West 47th Street. Most people assume you need a lab to tell a diamond from glass or a clever imitation. Often you just need to know where to look. Here are five things an expert notices first. If you're planning a Midtown visit this fall, you can try every one of them yourself on the tour.
1. How it plays with light
A well-cut diamond returns bright white light, flashes of color and crisp dark-and-light contrast as it moves. Glass looks glassy: pretty, but flat and a little sleepy. Cubic zirconia often goes the other way, with an almost "too rainbow" sparkle that looks like a disco ball.
Expert tip: Look at the stone under ordinary room light, not only under a jeweler's spotlight. Spotlights make almost anything sparkle.
2. The edges of the facets
Diamond is the hardest natural material on earth, so its facet edges stay sharp and crisp for generations. Glass and many imitations are softer. Under a loupe, their edges often look rounded, chipped or scuffed, especially on older pieces.
This is one of the first things Hemant teaches guests to check with a 10x loupe. Once you've seen a crisp diamond edge, you don't forget it.
3. What you see through it
With a loose, round diamond placed face-down on printed text, you usually can't read the words. A diamond bends light so strongly that the text breaks up. Glass and some imitations let you read the print more easily.
It's a fun trick, but not a final verdict. It only works on loose stones, and cut and shape change the result.
4. Doubled lines inside the stone
Moissanite is a popular diamond alternative, and it's beautiful in its own right. Under a loupe, you can often see a telltale "doubling": the facet lines at the back of the stone look slightly doubled, as if you're seeing double. Diamonds don't do this.
5. How it feels in the hand
Size for size, cubic zirconia is noticeably heavier than diamond. A dealer who has held thousands of stones can sometimes sense that difference. It isn't something a first-timer can rely on, but it's fascinating to see how much the trade still runs on trained eyes and hands.
The honest truth: some things need a lab
Lab-grown diamonds are real diamonds, with the same hardness and sparkle as mined ones. You can't tell them apart by eye or with a loupe. Professionals use specialized equipment and grading reports for that. So these five checks help you spot imitations, but they're no substitute for a trusted expert when you're buying.
Try it yourself on 47th Street
On The New York Tour of Diamonds, you don't just read about this. You'll learn how to hold a diamond with tweezers, look through a loupe the way a dealer does, and see a real stone up close on the most valuable block in Manhattan. The tour lasts 90 minutes and meets in the Diamond District, a short walk from Rockefeller Center, Radio City and Times Square.
- Great for: friends traveling together, women's clubs, corporate teams and anyone curious about the ring on their finger.
- No experience needed: Hemant explains everything in plain English.
- Easy to fit in: it slots neatly between lunch and a Broadway matinee.
Quick answers
Will I really hold a diamond? Yes. Learning to handle and inspect a stone is part of the experience.
Can I bring my own jewelry? You're welcome to wear it. It often leads to great questions.
Is this a sales pitch? No. The tour is about learning and enjoying the street.
Planning a fall trip to New York?
Tours run three times a day, Monday to Friday, and groups are kept small. Book your spot on The New York Tour of Diamonds before you travel, and learn to see diamonds the way the experts do.