Diamond Cut Grade: 6 Things You Need to Know

When it comes to choosing the perfect diamond, sparkle factor should be top of your list. Diamond cut grade is how well a diamond’s proportions are cut to emit maximum brilliance and fire. 

To make an informed decision, it’s important you understand the ins and outs of diamond cut grade to find the quality that fits your needs and your price range. 

We put together the top 6 things you need to know about diamond cut grade when shopping for a diamond engagement ring and answered the top frequently asked questions. 

1. What Is Diamond Cut Grade?

Diamond cut grade is the measurement of how a diamond’s facets interact with light and how well-proportioned the dimensions of a diamond are. This includes how the facets, surfaces and proportions are positioned and interact with light to create sparkle and brilliance. 

Three things are measured: scintillation—the amount of sparkle a diamond emits; fire—the scattering of white light; and brilliance—how the light is reflected from the diamond.

Since diamond cut refers to how well a diamond sparkles it’s the most important of all the 4Cs of quality—even more so than carat weight. Beyond the sparkle factor, the way a diamond is cut also affects the dispersion of light depending on the crown angle which can result in dark areas if not cut well. This is why it’s also important to be informed about your jeweler’s diamond cutters and ensure they follow a stringent cut grading system. 

2. What Is the Diamond Cut Grading Scale?

Understanding how a diamond’s proportions and dimensions interact with light also has to do with where a diamond falls on the cut scale. The Gemological Institute of America (GIA) cut scale ranges from poorly cut to ideally cut. Each grade differs in the amount of light return a diamond gives off which results in brilliance. 

Read the comprehensive guide to the diamond cut scale below to get a better understanding of the right diamond cut quality for you and your significant other. 

  • Super Ideal: Includes those with perfect dimensions and proportions. This impacts brilliance to dispersion and even scintillation. A Super Ideal diamond is the most sparkly of all the diamond cuts. 
  • Ideal: Comparable to the untrained eye to a Super Ideal diamond when it comes to brilliance and fire. The difference is related to minor light leakage. With an Ideal diamond, you can get the look of perfection at a slightly lower cost.
  • Very Good: Slightly less brilliant than Ideal but features good light return. A Very Good grade has less than ideal cut proportions that impact how light is returned. This is usually unnoticeable to the untrained eye and is one of the most popular cut grades.
  • Good: Feature proportions that are imperfect and may result in a slightly duller appearance, though the majority of light is returned. While not as brilliant as Very Good or Ideal diamonds, they look just as stunning to the untrained eye.
  • Fair: Have a visible reduction in brilliance and scintillation as their proportions are not perfectly symmetrical. Fair diamonds have light leakage, making them less sparkly to the untrained eye. Given the visible reduction in brilliance, we don’t sell any diamonds lower than Good at 12FIFTEEN. 
  • Poor: A Poor cut diamond allows significant light leakage. This makes it less brilliant than all other diamond cuts. These do not make good center stones and because of this, 12FIFTEEN does not sell Poor grades. 

3. What Is Diamond Scintillation?

There are a few diamond characteristics that affect brilliance and fire, one of which is scintillation. A diamond’s scintillation refers to how the light disperses when viewed in motion. This requires movement of the diamond, the light source, and the observer in order to see it in action. This is why jewelers often move diamonds back and forth in order to observe the scintillation. 

When it comes to observing scintillation, there are two types to look for: flash and fire. Flash scintillation is the dynamic pattern of white light observed across a diamond’s crown, whereas fire scintillation is the pattern of colored light observed across a diamond’s crown. One measures the dispersion of white light and the other color. Both of which are important when grading the brilliance of a diamond as a whole. 

A well-cut diamond will have ideal or almost ideal cut diamond facet proportions and depth in order to disperse the most amount of light. A poor-cut diamond will look dull to the eye due to the dark areas of poor light return. 

4. What Is Diamond Depth?

The depth of a diamond refers to its measurement from top to bottom. This includes the table of the diamond to the culet at the base. This is then calculated by dividing the total height by the width in order to get a percentage.  The deeper the diamond’s depth, the higher the diamond’s depth percentage.

A diamond’s depth has a huge impact on its appearance. While a shallow depth will allow most of the light to pass through, a deep depth can negatively impact light performance. 

A high-quality diamond will feature proportionate depth and facets—though the ideal range depends on the shape you choose. For example, round brilliant diamonds feature a perfect facet pattern and will have a different depth percentage than an emerald cut which is a step cut shape.

Here is a breakdown of the ideal depth percentage for the most popular diamond shapes. 

Diamond Shape Depth Percentages
Diamond Shape Ideal Depth Percentage
Round Brilliant Cut 59 to 62.6%
Princess Cut 68 to 75%
Cushion Cut 61 to 68%
Emerald Cut 61 to 68%
Asscher Cut 61 to 68%
Oval Cut < 68%
Pear Shape < 68%
Radiant Cut < 67%
Heart Shape 56 to 66%
Marquise Cut 58 to 62%

View the diamond shape and cut chart

5. Why Are Diamond Proportions Important?

Just how diamond depth affects the way facets interact with light reflection, a diamond’s proportions also impact visual appearance. Proportions influence everything from brilliance to fire and scintillation—all of the characteristics that inform how sparkly a diamond is.

A high-quality diamond will feature proportionate culet size, depth, table and facets. While a lower quality diamond will differ from stone to stone on proportions, anything lower than an Ideal cut will have less than perfect proportions. Many times this will perform similar to the untrained eye. But, keep in mind that Fair and Poor cut grades will be significantly less sparkly visually. 

This makes diamond proportions an important part of the diamond cut grade decision. Depth, scintillation and proportions are all essential characteristics to weigh when shopping for a diamond ring. 

6. What Is the Best Cut of Diamond?

When it comes to what is the best diamond cut grade, there is grading variation from jeweler to jeweler. This is because there is no consistent diamond grading scale which makes it difficult to get a true sense of quality. Jewelers use a variety of diamond certification agencies to grade their diamonds, including IGI, GIA, AGS and GCAL. 

While one jeweler may offer Super Ideal cut as their best diamond cut, another may offer Excellent. This affects the clear-cut answer of what is the best cut of diamond and can make reading the diamond cut chart challenging. 

At 12FIFTEEN, the best cut of diamond is Super Ideal. We developed our own stringent standard for accurately evaluating diamond cut. This includes closely reviewing all elements in a more comprehensive manner compared to other retailers—guaranteeing a truly accurate cut grade for every single diamond.

A Cut Above the Rest

Choosing the right diamond cut requires an evaluation of the quality and price point you’re looking for. A better cut grade will cost more but provide a better appearance. 

Then again, many consumers choose a slightly lower cut grade that looks almost perfect to the untrained eye. This is why Very Good and even Good cut grades are still an excellent diamond grade for the price. With lab grown diamonds vs. mined, you can get a better cut grade for the same, if not lower, price of mined diamonds. And, without the ethical or environmental implications, lab just makes sense.

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