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I am a second generation custom jeweller. I listen to people's story and turn it into a piece of jewellery that exceeds their expectations.
By Nick Coutu
Welcome to my comprehensive guide on the diamond cut chart, a crucial resource for understanding why cut reigns supreme among the “4 Cs.” My name is Nick Coutu, and I’ve spent years studying and working with diamonds—both mined and lab-grown. In this post, I’ll reveal how legendary mathematician Marcel Tolkowsky revolutionized the modern ideal cut, why “cut” is the single most important factor for maximizing sparkle and brilliance, and how you can use a diamond cut chart to make a savvy purchase that truly amazes.
When it comes to overall sparkle, cut outranks the other Cs. You can have a high-carat diamond, but if the facets are misaligned or the angles aren’t precise, the diamond will lack presence and underperform. Meanwhile, a smaller diamond with an excellent cut grade will exhibit breathtaking flashes of light (brilliance) and rainbow colors (fire).
This phenomenon stems from a diamond’s ability to reflect and refract incoming light. If the pavilion and crown are too deep or too shallow, light leaks out the sides or bottom. A precise cut ensures light gets bounced straight back into your line of sight. The result? That wow factor we all crave.
Pro Tip: A well-cut diamond often appears larger than its carat weight, thanks to superior light performance.
A diamond cut chart is an indispensable tool for visualizing the angles, proportions, and facet arrangements that maximize scintillation. The best gemological institutes, like GIA and IGI, base their cut grading systems on the research of many contributors. In my opinion, none is more compelling than Marcel Tolkowsky’s ideal proportions—the dimensions determined by his research. Maximizing a diamond’s brilliance, fire, and scintillation all hinge on alignment with the following proportions.
Below is a simplified diamond cut chart showing the recommended crown and pavilion angles for a round brilliant diamond. These angles ensure the best possible light return:
Keeping these metrics in check guarantees your diamond has that hypnotic sparkle. While these exact proportions are difficult to find, the following range represent the next grade in the chart after ideal, "excellent cut": A diamond cut chart typically highlights:
In a perfect world, each of these factors aligns with Tolkowsky’s ideal so that maximum brilliance, fire, and scintillation come alive in every facet of the stone.
Even slight deviations in angles can drastically affect light performance. If the crown angle is too steep, for instance, the diamond can look darker at the center. If the pavilion is too shallow, you lose that powerful internal reflection. A diamond cut chart helps you see what’s happening under the hood, allowing you to confirm whether the proportions meet the “ideal” or “excellent” thresholds.
The precision of angles, symmetry, and facet alignment is what ultimately makes or breaks a diamond’s visual allure.
In 1919, Marcel Tolkowsky published his doctoral thesis, “Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond.” Through rigorous math and physics, he pinpointed the optimal proportions for a round brilliant cut. His research gave us the fundamentals of the modern diamond cut chart, and gemological laboratories have refined these guidelines over time—but the core principles remain unchanged.
Fun Fact: Despite advancements in laser cutting and 3D modeling, Tolkowsky’s calculations still hold remarkable accuracy in explaining how diamonds achieve maximum sparkle.
While cut is the primary driver of brilliance, the other Cs—carat, color, and clarity—still play their parts. However, prioritizing cut can help you save money by slightly lowering color or clarity grades while still achieving a mesmerizing stone. A top-tier cut can mask minor inclusions and faint body color because the intense sparkle commands attention.
Want more insights? Check out my other posts:
These links will help you understand how to juggle all four Cs without sacrificing a diamond’s overall fire and brilliance.
Reputable labs like GIA and IGI assign a cut grade that usually falls into these categories:
Cut grading also takes symmetry and polish into account. Even if a diamond meets certain angles, poor facet alignment or finishing can reduce overall sparkle.
Remember: Without an excellent cut, you’ll lose the potential for maximum brilliance—even if the diamond is otherwise high in clarity or color.
Bonus Resource: Check out my other blog post, Best Diamond Shapes for Engagement Rings, to see how fancy cuts stack up against the round brilliant.
If you’re ready to see how these principles apply in real life, check out our Diamond showroom at LCJewellery.com. This page allows you to see the vast number of options you have and ability to narrow down to find your perfect balance of cut, color, carat, and clarity. What do your 4 Cs of a diamond look like? Feel free to send us a message for guidance if you need!
Recommendation: Choosing a certified diamond helps protect your investment and gives you peace of mind about the gem’s specifications, authenticity, and origin.
Hello! I’m Nick Coutu, a passionate second generation jeweler with over 20 years of experience in the diamond industry. My journey began my parents founded Lessard Coutu Jewellery in the same year that I was born. I was raised among sparkling beauty and intricate craftsmanship and lucky for me, diamonds are in my blood. Over the years, I’ve dedicated myself to educating clients, ensuring they feel both informed and confident in their jewelry choices. Through my blog, I aim to simplify complex topics, making them accessible and enjoyable for everyone—from first-time buyers to seasoned collectors.
Q1: Why is the diamond cut chart so important?
Because it visually breaks down the key angles and proportions that enable a diamond to reflect the most light, ensuring top-tier sparkle.
Q2: Does the diamond cut chart apply to fancy shapes?
Yes, but fancy shapes cannot be graded as Ideal. Although the angles differ from round brilliants, the concept of optimizing light return through specific proportions holds true for all shapes.
Q3: Can I rely on lab reports alone, or should I verify the chart myself?
Lab reports from GIA or IGI provide consistent, reliable data. However, reviewing a diamond cut chart can give you extra clarity and confidence when making your final selection.
Q4: Does Tolkowsky’s formula still apply today?
Absolutely. Modern technology fine-tunes the process, but Tolkowsky’s fundamental angles remain the gold standard for achieving maximum brilliance.
Q5: What if my budget doesn’t allow for a perfect cut?
Aim for at least “Excellent” in engagement rings, super important and statement pieces. "Very Good" cut diamonds are more acceptable for earrings, pendants, tennis bracelets, pavé, etc. You can adjust color or clarity to maintain your budget while still preserving brilliance.
Cut is the single most critical factor in a diamond’s appearance. By focusing on the diamond cut chart, you gain insight into how angles, proportions, and facet precision shape a stone’s brilliance, fire, and scintillation. Marcel Tolkowsky’s century-old research still influences today’s best cutters, ensuring every facet maximizes light return.
By understanding how to read and apply a diamond cut chart, you set yourself up for a purchase that truly captures the brilliance you deserve.
Links to More Insights
Thank you for reading! Be sure to explore our products at lcjewellery.com for diamonds meticulously aligned with Tolkowsky’s proven proportions.
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