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Nov 9, 2022

Diamond Proportions Guide: Why it Matters More Than Weight

Diamond weight, which is measured in carats, does not tell the full story. When it comes to diamonds, many people think that the bigger (weightier) the diamond, the better. However, this is not always the case. In fact, diamond proportions are usually more important than diamond weight.

This means that a diamond smaller in weight can be just as beautiful, valuable, and optically big as a diamond of larger carat size. This is because quality and cut play a large role in the final diamond's appearance. In this blog post, we will discuss why diamond proportions matter more than carat weight.

Cut Is the Most Important of the 4Cs

When it comes to diamonds, cut is the most important factor to consider. Even though cut is often used interchangeably with 'shape’, they are different. This is because the cut determines how well the diamond reflects light and sparkles. A well-cut diamond will have more brilliance and fire than a poorly-cut diamond of the same weight and shape. For round brilliant diamonds — the only shape with an official cut grading from a lab (IGI/GIA) — the cut grades are: Ideal (for IGI only), Excellent, Very Good, Good, Fair, and Poor (for GIA only). Each grade will affect the light performance and appearance of the stone's brilliance.

In addition to the cut, other factors can affect a diamond's sparkle. These include clarity, colour, symmetry, and polish. However, the cut has the most significant impact on sparkle from all of these factors. This is why proportions matter more than weight; they directly affect how well the diamond will reflect light and its lustre.

Cut grade is determined mainly by the stone's proportions, which are essentially the specific measurements of the diamond that affect how it sparkles. It is important to note here that even two diamonds of the same carat weight can have different face dimensions, which affects light performance and optical size. For example, a diamond's table size (the large flat facet on the top of the stone) affects how light enters the diamond and is reflected back to the viewer's eye. A small table size will cause light to leak out of the side of the stone, while a large table size will make the diamond appear dark.

When a diamond is cut to proper proportions, light is able to enter the stone and reflect back out, creating the stunning sparkle that we all know and love. However, if a diamond is not cut to proper proportions, the light will enter the stone but will not reflect back out correctly. This results in a dull, lifeless diamond. This is often referred to as the difference between a diamond with moderate depth and one that is too shallow or too deep.

Besides being more beautiful, diamonds that are cut to proper proportions are also more valuable. This is because these diamonds are rarer than those not cut correctly. Thus, if you are looking for a high-quality, valuable lab-grown diamond, be sure to pay attention to the diamond's proportions.

How Diamonds Are Cut and Polished

To further understand why a diamond's proportions matter more than weight, it's helpful to have a basic understanding of how diamonds are cut and polished. After a lab-grown diamond is formed, it's cut into a variety of different shapes.

The cutting process is done with a rotating wheel that is covered in abrasive grit. The diamond is slowly shaped into its finished form, which can take anywhere from hours to days. The most popular shapes include round, marquise, pear, oval, emerald, princess, and Asscher. If the diamond is not cut with precision, its facets may not reflect light evenly, resulting in a duller overall appearance.

After the cutting process is complete, the diamond is ready to be polished. This is where a skilled diamond cutter uses precise instruments to create symmetry and polish the diamond's surface until it shines.

The polishing process can have a major impact on a diamond's appearance. For instance, if the diamond is not evenly polished, it may appear darker in some areas and lighter in others. Finally, the diamond is inspected for quality and then sent off to be made into fine jewellery.

Choosing the Ideal Diamond Proportions

Now let's discuss how to choose a diamond with ideal proportions. First, it is crucial to understand the different parts of a diamond. The four main parts of a diamond are the crown, pavilion, girdle, and culet.

The crown is the upper part of the diamond, while the pavilion is the lower part. The girdle is the narrow band that goes around the middle of the diamond, and the culet is the small point at the bottom of the pavilion.

When choosing a diamond's cut, you should look for one with a well-proportioned depth % and table % in your IGI/GIA grading report. For a round cut diamond, the total depth percentage is ideally 59 to 62% (the diamond depth divided by the diamond's diameter), and the table percentage is ideally 53 to 60% (the length of the table divided by the diamond's diameter).

The width of the girdle is also important – avoid anything with the extremely thin or extremely thick designation. As the ideal or excellent diamond proportion changes based on the particular diamond shape, check out a diamond proportion guide below. When looking at your certificate, ensure your diamond sits in the ideal to excellent range:

Ideal/Excellent Proportions Based on Diamond Shape

Lab-Grown Diamond Shape Depth Percentage Table Percentage
Asscher 61 to 67 61 to 69
Cushion 61 to 67 61 to 67
Emerald 61 to 67 61 to 69
Heart 58 to 62 53 to 63
Marquise 58 to 62 53 to 63
Oval 58 to 62 53 to 63
Pear 58 to 62 53 to 63
Princess 64 to 75 67 to 72
Radiant 61 to 67 61 to 69
Round 59 to 62.3 53 to 58

Click here for the full table of each diamond shape and the various cut grades based on different proportions.

As well as paying attention to the depth % and table % for diamond proportions, you should also ensure that the diamond has a small culet. A small culet ensures that light will enter and exit the diamond correctly, resulting in maximum brilliance and fire. The culet should be graded as "none" or "pointed" on your GIA/IGI grading report.

Now you know why diamond proportions matter more than carat weight and how to choose the ideal diamond proportions. This will assist you in finding the perfect lab-grown diamond for your needs. For ideas, get inspired by Cullen Jewellery’s latest lab-grown engagement ring collection today!


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