Natural Diamond Prices – January 2025
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Diamond symmetry plays a critical role in determining the overall uniqueness and value of a diamond. While many buyers focus on cut, color, and clarity, symmetry is an important factor influencing how a diamond interacts with light. In this guide, we’ll explore how symmetry is graded, why it matters, and how it impacts both appearance and price.
What Is Diamond Symmetry?
Diamond symmetry refers to the precise alignment and proportion of a diamond’s facets. When a diamond is cut with excellent symmetry, its facets work together to enhance light reflection, resulting in maximum brilliance, fire, and scintillation. Conversely, imperfections in symmetry can affect how light interacts with the diamond, potentially diminishing its visual appeal.
Bad Diamond Symmetry
Excellent Diamond Symmetry
Image Source: Whiteflash
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How Is Symmetry Graded?
Symmetry is evaluated using a non contact scanner that takes 400 black and white profile high resolution images while the diamond is rotated, with a step motor, on a turntable stage. The diamond is held in place with a vacuum suction. From this process extremely accurate 3D models are built and every facet’s angle and azimuth (the compass direction it faces) are measured.
Sarine Scan Device – Image Source: Whiteflash
Helium Scanner – Image Source: Lexus India
Typically conducted by reputable gemological labs like the Gemological Institute of America (GIA) and the American Gem Society (AGS). Both organizations assign symmetry grades based on specific criteria, such as:
- Facet Alignment: Ensuring that all facets are properly aligned and proportionate.
- Proportions: Evaluating the diamond’s overall proportions, including crown and pavilion angles.
- Girdle Thickness: Assessing the consistency and uniformity of the girdle.
- Table Centering: Checking if the table is centered and properly positioned.
- Culet Alignment: Confirming that the culet is centered and aligned with the diamond’s axis.
- Facet Shape: Ensuring all facets are symmetrical and identical in shape and size.
- Polish Quality: Reviewing the finish of the diamond for any marks or imperfections that impact symmetry.
Symmetry Grades
Most labs assign symmetry grades as follows:
- Excellent(or AGS Ideal): Facets align with near-perfect precision.
- Very Good: Minor symmetry flaws that are difficult to detect without magnification.
- Good: Visible symmetry flaws that slightly affect the diamond’s appearance.
- Fair: Noticeable symmetry issues that detract from the diamond’s brilliance.
- Poor: Significant symmetry flaws that severely impact light performance.
Image Source: Whiteflash
Interestingly, the GIA allows diamonds with one grade lower symmetry (and or polish) to still achieve a higher cut grade as long as the proportions meet those criteria. The AGS, however, requires Ideal Symmetry (one grade stricter than Excellent) for its highest cut grade, AGS 0.
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The Relationship Between Symmetry and Diamond Cutting
When polishing a rough diamond, cutters often prioritize maximizing carat weight over achieving perfect symmetry. This decision might involve avoiding inclusions or reaching a “magic weight” like 1.00 carat. These trade-offs can result in:
- Slightly off-round shapes
- Uneven girdle thickness
- Tilted or off-center tables and culets
Contrary to popular belief, minor symmetry imperfections are not always due to poor technique. Instead, they often reflect the cutter’s expertise in balancing weight retention and optical performance.
Optical Symmetry: A Key Consideration
Beyond lab-graded symmetry, optical symmetry, how a diamond’s symmetry impacts its light performance can be assessed using tools like the Ideal-Scope. High-optical-symmetry diamonds display balanced and symmetrical light patterns, with the most notable example being Hearts and Arrows diamonds. These diamonds are celebrated for their near-perfect optical symmetry, offering exceptional brilliance and precision.
Does Symmetry Impact Price?
Symmetry grades can significantly influence a diamond’s price. For example, a GIA-certified round diamond with Excellent symmetry often commands a premium over those with Very Good or Good grades. Here’s a general guideline based on a study of round diamonds (1-1.49 carats, F-H color, VS1-SI2 clarity, GIA or AGS certification):
Polish & Symmetry Grade | % Price Difference |
Ex/Ex or Id/Id | 0% |
Ex/VG or Id/VG | -6.5% |
VG/VG | -8.3% |
VG/G | -9.8% |
G/G | -11.6% |
Although symmetry impacts price, it is often secondary to cut proportions in determining a diamond’s beauty.
Symmetry vs. Cut: What Matters Most?
While symmetry is important, it’s just one element of a diamond’s overall cut quality. Critical factors like facet angles, table size, and depth ratios typically have a greater effect on brilliance and fire than minor symmetry flaws. For many buyers, a diamond with Very Good symmetry and excellent proportions can be a stunning and cost-effective choice.
Final Thoughts
Diamond symmetry is a crucial factor to consider when evaluating a diamond’s overall quality. However, it’s essential to balance symmetry with other factors like cut proportions and light performance. Tools like the Ideal-Scope and certifications from reputable labs can help you assess both symmetry and optical performance.
Get the best value for your money with high quality diamonds: Visit PriceScope’s Diamond Search or join our online community to learn more about selecting a diamond that meets your needs and budget.
