Cubic zirconia (CZ) is a popular diamond substitute that closely resembles diamonds in appearance. However, there are several key differences between the two that can help you distinguish them. Whether you’re shopping for jewelry or trying to assess the authenticity of a stone you already own, knowing how to tell cubic zirconia from diamonds is crucial. In this article, we’ll explore various methods to make this distinction, from simple visual inspections to more technical tests.
Visual Inspection
Brilliance and Sparkle
One of the first things you can notice when comparing cubic zirconia and diamonds is their brilliance and sparkle. Diamonds have a unique sparkle that comes from their high refractive index and the way they interact with light. When light enters a diamond, it undergoes internal reflection and dispersion, creating a beautiful play of light known as “fire.” A diamond’s sparkle is often described as sharp, intense, and with flashes of different colors that change as the stone is moved.
Cubic zirconia, on the other hand, also has a good amount of sparkle but it tends to be more “glassy” or overly bright in comparison. The light dispersion in CZ is different from that of a diamond, and it may not have the same depth and complexity of color flashes. For example, when you hold both a diamond and a cubic zirconia under a light source and turn them slowly, the diamond will show a more lively and nuanced display of light, while the cubic zirconia might seem to have a more uniform and less captivating sparkle.
Cut and Faceting
Examine the cut and faceting of the stones. Diamonds are cut with extreme precision to optimize their light performance. The facets on a diamond are usually sharp, clean, and well-defined. A well-cut diamond will have proportions that allow light to enter through the top, bounce around inside the stone, and exit back out in a way that maximizes its brilliance.
Cubic zirconia can also have well-defined facets, but sometimes the cutting may not be as precise as that of a high-quality diamond. When looking closely with a magnifying glass or a jeweler’s loupe, you might notice that the edges of the facets in CZ are slightly less sharp or that the overall symmetry of the stone is not as perfect as in a diamond. This can affect how the light interacts with the stone and is a telltale sign when making a comparison.
Inclusions and Imperfections
Natural diamonds often have inclusions, which are tiny internal flaws that occurred during their formation. These inclusions can be visible under magnification and can range from small crystals to fractures or other irregularities. Using a jeweler’s loupe or a microscope, you can look for such inclusions within the stone.
Cubic zirconia, being a synthetic material, is typically created in a more controlled environment and is more likely to be free of inclusions or have fewer and different types of imperfections compared to natural diamonds. However, some lower-quality cubic zirconia may have small bubbles or other manufacturing artifacts that can be spotted under magnification, but these are usually different in nature from the inclusions found in diamonds.
The Fog Test
How to Perform the Test
The fog test is a simple and easy way to start distinguishing between a diamond and cubic zirconia. To conduct this test, simply breathe on the stone as if you were fogging up a mirror. The moisture from your breath will form a thin layer of condensation on the surface of the stone.
Immediately after fogging it up, observe how quickly the fog dissipates.
Rationale and Results
Diamonds have excellent thermal conductivity. This means that they quickly conduct heat away from the surface. So, when you breathe on a diamond, the fog formed by your breath will disappear almost instantly, usually within a second or two.
Cubic zirconia, on the other hand, has much lower thermal conductivity compared to diamonds. As a result, the fog will linger on the surface of the cubic zirconia for a longer period, typically several seconds before it finally dissipates. This difference in how quickly the fog clears is a clear indicator to help tell them apart.
The Scratch Test
Cautionary Note
The scratch test should be done with great care as it can potentially damage the stone if it’s a diamond or any other valuable gemstone. This test involves using a material of known hardness to try to scratch the surface of the suspected stone.
It’s advisable to use only materials that are softer than a diamond on the Mohs scale of hardness, such as a piece of quartz or a hardened steel file.
Performing the Test
Gently attempt to make a small scratch on an inconspicuous part of the stone, like on the underside if it’s in a setting. If the stone is able to scratch the softer material without getting scratched itself, it could be a diamond.
Diamonds are the hardest known natural material, rating a 10 on the Mohs scale of hardness. They can scratch almost any other common material. Cubic zirconia, on the other hand, has a hardness of around 8 to 8.5 on the Mohs scale. While it’s relatively hard, it can still be scratched by a diamond and won’t be able to scratch a diamond in return. However, keep in mind that there are other synthetic materials with similar hardness levels, so this test isn’t always definitive on its own but can be a useful part of the overall assessment.
The UV Light Test
How UV Light Affects Each Stone
Many diamonds exhibit fluorescence under ultraviolet (UV) light. When exposed to UV light, some diamonds will emit a visible glow. The fluorescence can vary in color, ranging from blue to yellow, green, or even white. However, not all diamonds fluoresce, and the intensity of the fluorescence also varies from stone to stone.
Cubic zirconia usually does not fluoresce in the same way as diamonds under UV light. While some cubic zirconia may show a very faint glow or no fluorescence at all, the appearance and behavior under UV light are generally different from that of diamonds.
Performing the Test
You can use a UV flashlight, which is easily accessible in many stores or online. Shine the UV light on the stone in a dark room and observe if it glows and what the nature of the glow is. If the stone shows a distinct fluorescence pattern that is typical of diamonds (such as a soft blue glow), it could be an indication that it’s a diamond. But if there’s no fluorescence or it has an unusual or very weak glow that doesn’t match the characteristics of diamond fluorescence, it’s more likely to be cubic zirconia.
Density Test
Measuring Density
The density test involves determining the density of the stone to see if it matches that of a diamond or cubic zirconia. To measure the density, you first need to know the weight and volume of the stone. Weigh the stone accurately using a precision scale that can measure small weights in grams or carats.
To find the volume, you can use the displacement method. Fill a graduated cylinder with a known amount of water and carefully drop the stone into it. Note the increase in the water level, which represents the volume of the stone. Calculate the density by dividing the weight by the volume (density = weight/volume).
Comparing Densities
The density of a diamond is approximately 3.52 grams per cubic centimeter. Cubic zirconia, on the other hand, has a higher density, typically around 5.6 to 6 grams per cubic centimeter. If the calculated density of the tested stone is close to 3.52 g/cm³, it’s more likely to be a diamond. If it’s closer to the density range of cubic zirconia, then it’s probably cubic zirconia. However, this test can be challenging to perform accurately at home as it requires precise measurements and specialized equipment like a good quality graduated cylinder and a sensitive scale.
Professional Gemological Testing
Gemological Laboratories
For a conclusive determination of whether a stone is a diamond or cubic zirconia, it’s best to send it to a professional gemological laboratory. Reputable labs such as the Gemological Institute of America (GIA), the International Gemological Institute (IGI), and the American Gem Society (AGS) have trained gemologists and advanced equipment to conduct thorough tests.
These labs use various techniques, including spectroscopy, which analyzes the light absorption and emission characteristics of the stone to determine its chemical composition and crystal structure. They also examine the stone’s physical properties in detail, such as its hardness, refractive index, and other aspects that are unique to diamonds or cubic zirconia.
What the Tests Reveal
Through spectroscopy, the lab can identify the specific elements present in the stone and their concentrations. Diamonds are composed mostly of carbon, while cubic zirconia is made of zirconium oxide. Any deviation from the expected elemental composition can clearly indicate whether the stone is a diamond or cubic zirconia.
Additionally, the labs measure the stone’s refractive index accurately. A diamond has a specific refractive index range, and cubic zirconia has its own distinct range. If the tested stone’s refractive index value falls within the range typical of cubic zirconia rather than that of diamonds, it’s conclusive evidence that it’s cubic zirconia. Professional testing provides the most accurate and reliable way to distinguish between the two.
Considering the Source and Documentation
Provenance and Origin
Knowing the source of the stone can give you some clues about whether it’s likely to be a diamond or cubic zirconia. If the stone was purchased from a reputable jeweler with proper documentation, such as a certificate from a recognized gemological laboratory, it’s more likely to be a diamond. Reputable jewelers follow strict ethical and quality standards and are less likely to sell cubic zirconia as diamonds.
On the other hand, if the stone was acquired from an unknown or untrustworthy source, like a street vendor or an online marketplace with no guarantees, there’s a higher risk that it might be cubic zirconia or some other diamond substitute.
Certificates and Appraisals
A diamond certificate issued by a professional lab contains detailed information about the stone’s characteristics, including its cut, clarity, color, and carat weight, as well as verifying its authenticity. When buying a diamond, always ask for a certificate if available.
An appraisal, which estimates the value of the stone but also assumes its authenticity, can also be helpful. However, an appraisal alone isn’t a foolproof way to confirm that a stone is a diamond, but it can be useful in conjunction with other methods of testing.
Conclusion
Telling the difference between cubic zirconia and diamonds requires a combination of different methods. While simple at-home tests like visual inspection, the fog test, the UV light test, and the scratch test can give you some initial indications, they are not always conclusive. More advanced techniques such as density testing and professional gemological testing are the most reliable ways to make a definitive determination. Additionally, considering the source of the stone and any available documentation is also important in the overall process of distinguishing between these two. By using these various approaches, you can be more confident in identifying whether a stone is a diamond or cubic zirconia and avoid any potential misunderstandings or misidentifications in the world of gemstones and jewelry.
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