Diamond Cut – why it’s the most important of the 4Cs

When shopping for an engagement ring, one of the most critical aspects to consider is the diamond’s ‘cut’ quality.

A diamond’s cut is what determines how much light it reflects and therefore how much it sparkles. greatly influences its overall appearance, brilliance, fire, and scintillation.

Of the 4C’s that value a diamond – Cut, Colour, Clarity and Carat Weight, the Cut is probably the most under-estimated and yet has the biggest impact on the sparkle of a diamond.

In this guide, you’ll learn about diamond cut quality from a point of view of buying a diamond ring. We’ll mainly focus on the GIA grading scale for round brilliant diamonds, but will also look at the importance of proportions in other diamond shapes.

What is Diamond Cut Quality?

Diamond cut quality refers to the skill and precision with which a diamond has been shaped and faceted into its final form.

While there is a lot of technology involved, cutting and polishing a diamond from a rough stone to a brilliant gem is still a manual process and as a result there can be considerable variation in the final proportions of diamonds and the quality of the finish. Collectively, this is known as the diamond’s ‘make’.

The GIA Grading Scale for Round Brilliant Diamonds

As with the other 4Cs, to make it easy to understand the quality of a diamond, and compare diamonds to each other, a simple scale is used across the majority of the industry.

The scale was originally created by the Gemological Institute of America (GIA), and applies only to round brilliant diamonds. The GIA cut grading scale includes the following categories:

• Excellent
• Very Good
• Good
• Fair
• Poor

Each grade reflects the diamond’s overall cut quality and its ability to reflect light, with an “Excellent” cut providing the most brilliance and fire. It should be noted that ‘Excellent’ is sometimes called ‘Ideal’ by some retailers. However, the terms are interchangeable.

If you are choosing a round brilliant diamond for your engagement ring, choosing a diamond with an ‘excellent’ cut is generally recommended to maximise the sparkle of the stone.

Some retailers offer ‘Super Ideal’ diamonds that have been specially selected by their own gemologists and may offer super ‘light performance’ to regular excellent cut diamonds. These often have a higher price attached to them and may warrant more investigation e.g. evidence of light performance using an ASET tool or Idealscope.

Proportions, Symmetry and Polish in Diamond Cut Quality

In addition to the overall cut grade, a diamond proportions and symmetry play a significant role in a diamond’s cut quality.

Proportions refer to the various dimensions of the diamond, such as table size, crown angle, and pavilion depth. These proportions affect how well a diamond reflects and refracts light, which in turn influences its overall appearance and value.

If a diamond is cut just right, light will be transmitted through the top table (flat area on top of the diamond), be reflected from the bottom ‘pavilion’ facets, and transmitted back through the table and top ‘crown’ facets in the form of brilliant sparkle.

As more time is required for the most skilled diamond cutters, and more of the rough material must be sacrificed in order to produce ideal cut diamonds the final product is considered very valuable. The ideal cut diamonds hold more value in comparison to Deep or Shallow cut diamonds.

If the diamond is cut to be overly shallow, light will be able to travel all the way through the bottom facets and be lost, reducing the sparkle.

If the diamond is cut to be too deep, light will be reflected at the wrong angle and will be transmitted from the side of the diamond, reducing the sparkle. The diamond may appear darker in the centrDeeper diamonds also look smaller when viewed from above as well, which is undesirable.

Diamond Symmetry

Diamond symmetry refers to the arrangement and alignment of a diamond’s facets, as well as the overall balance and proportionality of its shape.

It is basically an evaluation of how precisely the facets of a diamond are aligned with one another, and is graded on the poor – excellent scale, just like diamond cut.

Symmetry is important because the better the symmetry of a diamond is, the more accurately the facets interact with light, which means less light is lost and more can be returned back to your eye as sparkle, brilliance and fire.

While ‘fancy’ shaped diamonds (such as pear, oval, marquise, cushion, etc.) aren’t given a grade for overall diamond cut quality, they are given a grade for symmetry. For these shapes, symmetry can be more subjective and less standardised, but is still important in determining the overall beauty and light performance. Misaligned or uneven facets can create dark areas, called “bow-tie” or “butterfly” effects, which may diminish the diamond’s overall appeal.

Diamond Polish

The final factor relating to cut that will appear on a diamond’s certification is a ‘polish’, which is a measure of the quality of the surface finish on a diamond. When a diamond is cut and shaped, the cutter polishes the facets (or faces) of the diamond to remove any surface imperfections, such as scratches or nicks, and to give the diamond a smooth, reflective surface.

As with the overall diamond cut grade, polish is graded from “Excellent” to “Poor.” While having a high polish grade can enhance the beauty and sparkle of a diamond, it is generally regarded as a more minor factor as differences in polish grades are not easily noticeable to the unaided eye, especially when the diamond is set in a piece of jewellery.

That being said, some people do place great importance on obtaining a Triple X diamond, as it represents the highest level of craftsmanship and attention to detail.

• Excellent cut
• Excellent symmetry
• Excellent polish

Diamond Cut Quality and Other Shapes

While the GIA cut grading scale is exclusive to round brilliant diamonds, cut quality and proportions are still crucial factors to consider for ‘fancy’ shaped diamonds ie. any other shape except round.

The ideal proportions for fancy shaped diamonds can vary, but they all have a significant impact on the diamond’s appearance and value. Here are some examples of fancy shaped diamonds and their ideal proportions:

• Princess cut diamond: Look for a Look for a depth percentage between 68% and 75% and a table percentage between 62% and 68% length-to-width ratio of around 1:1, with even facet alignment and sharp corners.
• Emerald: Aim for a length-to-width ratio of 1.3:1 to 1.5:1, with parallel step facets and even corners.
• Oval: Look for a length-to-width ratio of about 1.35:1 to 1.5:1, with an even outline and well-balanced facets.
• Cushion cut: Opt for a length-to-width ratio of 1:1 for a square cushion or 1.1:1 to 1.3:1 for a rectangular cushion, with a symmetrical outline and consistent facet arrangement.
• Pear: Look for a length-to-width ratio of around 1.5:1 to 1.75:1, with a well-rounded base and smooth, even curves.

The Impact of Cut Quality on Diamond Value

A diamond’s cut quality and grade can significantly affect a diamond’s value –  a well-cut diamond will generally be more desirable, and therefore more valuable than a poorly cut one.

When researching diamonds and comparing different stones’ value, it’s essential to consider what is important to you, and strike the right balance between cut quality and other factors, such as carat weight, clarity, and colour.

For example, a smaller diamond with an excellent cut is likely to appear more brilliant than a larger diamond with a poor cut. However, which of the two diamonds is right for you is a personal decision.

The Importance of Certification for Diamond Cut Quality

A diamond grading report or certification from a reputable entity verifies its cut quality, along with other quality factors, such as carat weight, clarity, and colour.

Some of the most reputable certification entities include:

• GIA – the Gemological Institute of America
• AGS – the American Gem Society
• EGL – European Gemological Laboratory
• HRD – Hoge Raad Voor Diamant, which means ‘Diamond High Council’ in Flemish

Obtaining a certification for both round brilliant and fancy shaped diamonds is crucial, as it provides an unbiased assessment of the diamond’s quality, ensuring you get what you pay for. Always verify the certification and double-check that it matches the diamond’s characteristics before making your purchase.

Common Diamond Cut Issues to Watch Out For

When shopping for a diamond, be aware of common cutting issues that can negatively affect a diamond’s appearance and value. These issues include:

• Too shallow or too deep cut: A diamond cut too shallow or too deep will not reflect light optimally, reducing the amount of light it reflects and resulting in a lack of brilliance and fire.
• Poor symmetry: A diamond with poor symmetry will have misaligned or uneven facets, reducing its overall light performance and beauty.
• Off-centre culet: An off-centre culet (the small point at the bottom of a diamond) can cause the diamond to appear unbalanced and negatively affect its light performance.

To avoid these issues, closely examine the diamond’s proportions, symmetry, and overall appearance. Consult with an expert and refer to the diamond’s certification to ensure its cut quality meets what you are looking for.

Choosing the Right Cut Quality for Your Engagement Ring

When selecting the diamond cut quality for your engagement ring, there are many factors to consider – personal preferences, budget, and desired diamond characteristics. Here are some general guidelines to help get a great looking diamond.

• Prioritise cut quality: Cut quality plays a significant role in determining a diamond’s overall beauty as it’s the main thing that determines how much the diamond will sparkle. It’s generally accepted to be the most important of the 4Cs.
• Consider your budget: While a higher cut grade may be more desirable, it’s essential to balance this preference with your budget. You may need to compromise on other factors, such as carat weight or clarity, to afford a diamond with a better cut quality.
• Understand the ideal proportions for fancy shapes: If you’re interested in a fancy shaped diamond, research the ideal proportions for that specific shape to ensure optimal light performance and beauty.
• Seek expert advice: Consult with a knowledgeable jeweller or gemologist who can guide you in selecting a diamond with the best cut quality for your budget and preferences.