How to Tell the Difference between a Diamond and a Cubic Zirconia

How to Tell the Difference between a Diamond and a Cubic Zirconia
In Diamonds, Jewelry, Travel
Diamond | Kruckemeyer & Cohn Jewelry Company

Today there are a number of man made stones that come close to matching the appearance and characteristics of diamonds. Cubic zirconium (CZs) are less expensive and look more like diamonds than any other man made jewel. In fact, when looking at a stone with the naked eye, many gemologists have trouble telling diamonds and CZs apart. However, CZs are not as heat resistant as diamonds and can crack and burn at high temperatures.  Also CZs scratch more easily, and with time they start to look worn. So how can a couple shopping for an engagement ring tell if the jewel they want to buy is a genuine diamond?

  1. To start with shop at a reputable jewelry store.

    Is this a real Diamond

    Is this a real Diamond

  2. Make sure that the stone you wish to purchase is graded by the Gemological Institute of America (rated for color, cut, carat, and clarity).
  3. Look at the stone’s setting. CZs are much cheaper than diamonds and usually affixed to an inexpensive setting. If the stone’s support appears loose, crooked, or unattractively placed, that maybe an indication it’s a CZ and not a diamond.
  4. Use the fog test. Diamonds are rapid conductors of heat, so if you breathe on one, the fog should dissipate immediately. Not so with CZs and other fake diamonds that may stay fogged for a couple of seconds.
  5. Now use a loupe (10x magnifier) to check for damage and imperfections in the stone. CZs, which are made by manufacturers, appear flawless, whereas most diamonds will have tiny imperfections. A diamond with no imperfections will sell for many thousands of dollars (ten to one hundred thousand dollars or more). So if the store is trying to sell you a flawless stone for two hundred dollars, for example, you can be sure it’s a CZ.
  6. While examining the stone under a loupe, look at the facet edges. If it’s a diamond, you will see that the facets have sharp edges. If it’s a CZ, on the other hand, the facets will have rounded edges.
  7. Next do the ultraviolet test. Most diamonds (except the most expensive) will glow a shade of blue under ultraviolet light. CZs, on the other hand, will glow no color or many colors.
  8. Now look at how the stone refracts light. Diamonds refract light into contrasting shades of grey, whereas CZs refract light into multi-colored rays. Many diamonds do display some colored reflections, due to inclusions (the diamond’s fire); however, if the stone you are examining has all the colors of the rainbow, it’s likely a CZ.
  9. Because of the many ways in which a diamond refracts and internally reflects light, it should not be transparent. If you turn a diamond upside down and hold it over print, you shouldn’t be able to read the letters. Not so with a CZ.

If you’re really stumped about a stone, get a second opinion from a jeweler whom you trust. *******************************************************************************     CZ comes closer than any other gem material to matching the characteristics of a diamond Most people, even trained gemologists, cannot tell the difference between diamond and CZ, with the naked eye. CZ appears to have slightly less brilliance (or sparkle) than a diamond, and more fire, or flashes of color. In addition, cubic zirconia is not as resistant to heat as diamonds and can easily crack and burn under high temperature. Since cubic zirconia scratches more easily, with time, it starts to look worn. You should also keep in mind that this stone is more brittle than diamond and i CZ and diamonds can both be colorless, or they can be tinted with yellow, pink, blue, or another tone f you take a close look at a diamond’s facets, you will notice that their edges are very sharp. In contrast, the facets of a cubic zirconia stone have smoother and rounder edges. Since cubic zirconia is cheap, it is also often set in cheap mountings. Jewelers usually have diamond testers, which are small electronic devices that can detect Zirconia, and if you ask to have your stone tested, you can find out the truth immediately, for a small fee.

  • Understand Diamond Quality: Couples who know how to judge stonequality by the four Cs — color, cut, carat, and clarity as defined by the Gemological Institute of America — are less likely to be fooled by false gems because they can immediately discern poor quality imitations.
  • Work with Reputable Jewelers: A well-respected jeweler who can answer detailed questions is less likely to be involved with fake diamonds and shady deals.
  • Check Setting Quality: Diamonds are expensive gems, and true diamonds are rarely set into inferior metals with poor security or placement. If an engagement ring’s setting is crooked, loose, or poorly crafted, the stone may be less valuable than advertised.
  • Fog Test: Diamonds disperse heat rapidly and a light huff of breath on the stone should fog it up but that fog will vanish almost instantly. Fake diamonds may stay fogged for 2 seconds or longer according to National Jeweler’s Supply.
  • Check for Damage: Diamonds are very durable gems, and while they are not impervious to surface damage, a stone that shows a lot of nicks, scuffs, scratches, or other damage is less likely to be a real diamond.
  • Reflection Color: Because of the refraction index of diamond, the reflection and sparkles within the stone should be in shades of gray. According to, stones that have rainbow reflections are likely not genuine diamonds.
  • Transparency Test: Diamonds should not be truly transparent. Stone Cutters International recommends turning loose diamonds upside down over a newspaper or other piece of paper with typed words printed on it. If you are looking at a real diamond, you will typically not be able to read the text through the stone. If you can read the text, the stone you are looking at does not have the proper light dispersion properties a real diamond possesses.
  • Ultraviolet Light: The majority of diamonds will glow blue under ultraviolet lights such as black light. Fake diamonds, on the other hand, will glow other colors or not at all. While an extremely high quality gem will also not glow under UV light, this can be a good test for questionable stones.
  • Perfection: Any natural stone will have some minute flaws and inclusions, and a gem that is perfectly flawless should be examined with great care to be sure it is real rather than being lab-created. While real flawless diamonds are available, if the stone in question is offered at an unforgettably affordable price, it may not be a real gem.
  • Loupe Examinations: Use a jeweler’s loupe to examine the diamond closely. A real stone should have sharply defined facets with precise geometry, while fake stones may be less well crafted. On a real diamond, the stone’s thin girdle will also be faceted, and some designer diamond shapes such as the Hearts on Fire diamond will have identification numbers inscribed along the girdle.
Cushion cut-Diamond1

Is this a real Diamond ?

Being that CZ has a refractive index of 2.176, compared to a diamond’s 2.417, diamonds are therefore said to be brighter than CZ. Contemporary production of CZ is virtually flawless, whereas diamond usually contains impurities and inclusions, or have some sort of defect, be it a feather, included crystal, or perhaps a remnant of an original crystal face (e.g. trigons). In regards to color-more precisely, the lack of color-only the rarest of diamonds are truly colorless, as most have a tinge of yellow or brown to some extent. By comparison, CZ in most cases can be made entirely colorless, equivalent to a perfect “D” on diamond’s color grading scale. With a dispersion power greater than diamond (0.060 vs. 0.044), the more prismatic fire of CZ can be seen by even an untrained eye. While one is obviously naturally formed and the other is a man-made impostor, telling the difference between the two can be difficult if you don’t know what you’re looking for. The most conclusive way to tell the difference is with an electronic device that reads the stone’s electrical and thermal conductivity, but you can also look at the surface of the stone for any tell-tale scratches (diamonds shouldn’t have any), the color of the stone’s refraction (the light of a diamond will refract gray), and for flaws that will suggest a naturally made stone. Other tests include breathing on the stone, putting it under a black light, and trying to scratch glass with it. One of the most time-honored tests used by gemologists is still one of the most effective. Place the stone on a newspaper. Because a real diamond refracts light—a lot—it’s impossible to read letters through it. Many cubic zirconia you’ll be able to make out letters through. Another easy test is to breathe on the stone. Diamonds don’t retain heat, so they’ll become almost instantly clear again. Cubic zirconia tends to retain heat longer than a diamond and will stay cloudy.   A cubic zirconia is about 50 percent heavier than a real diamond. a CZ will weigh approximately 1.75 times more than a diamond of equivalent size.

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