Diamond Culet: What is it & How Does it Impact a Diamond’s Cut Grade?

Diamond culet: Often unseen, but always important...

While searching for a diamond, many shoppers don’t pay much attention to a stone’s culet. After all, once a diamond is in its setting, no one will even see it, right? But, a diamond’s culet—or lack thereof—plays an important role in the gem’s overall appeal and brilliance.✨ So how does a diamond’s culet impact its sparkle, and is it important to have one at all?

Let’s look at:

  • Diamond culet basics
  • Grading a diamond culet
  • How culets present in antique and modern diamond cuts
  • The impacts of a diamond’s culet on appearance and value
  • Why do noticeable culets still exist today?
  • How to spot a diamond culet
  • Which culet grade you should choose
Diamond Culet Education
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Basics: What is a diamond culet?

A culet (pronounced kyoo-lit) is the small point at the very tip of your diamond where all the pavilion facets meet, and it comes in a few different forms. The most common style of culet today is the “pointed culet” which is when all of the facets come together to form a perfect point. However, some diamond styles have an “open culet” or “polished culet”, which is an additional, flat facet—instead of a pointed tip—that runs parallel to the diamond’s table.

Because diamonds with polished culets have an extra facet at the bottom of the stone, a round brilliant diamond with an open culet has 58 facets instead of the typical 57. Other diamond shapes with polished culets also have an extra facet in their total facet count which can be found in their diamond grading reports.

However, some fancy shapes, such as emerald-cut diamonds, do not have a culet at all! Instead, they have a “keel” which acts like the keel at the bottom of a boat. This long ridge spans the length of the diamond and runs parallel to the stone’s longest edge, acting as a meeting point for the two longest sides.

Understanding diamond culet sizes and grading

The GIA and other labs grade diamond culets based on their size, and they have some standardized ways of measuring the culet to provide accurate data. First, gemologists inspect the diamond—positioned table up—under 10x magnification to gain a general sense of culet size.

Then, if a culet is present, gemologists can use a non-contact optical measuring device or a GIA Multi-Purpose Gemological Reticule and a standard microscope to measure the culet. The GIA notes that culet size is defined as the width of the culet—if present—relative to the average girdle diameter of a round diamond.

The size of the culet is expressed by a simple equation:

Culet Size % = [Culet Size (mm) / Average Diameter] × 100

Once the culet is measured, a proper grade can be awarded. The GIA has an International Diamond Grading System that allows gemologists to assign the following grades according to a culet’s size:

GIA Culet GradeDescription
NoneNo culet facet is present; the diamond has a “pointed” culet
Very SmallThe culet is less than ≈ 1.5% of the gem’s average diameter
SmallThe culet is ≈ 1.5% of the gem’s average diameter
MediumThe culet is ≈ 3.0% of the gem’s average diameter
Slightly LargeThe culet is ≈ 5.0% of the gem’s average diameter; at this point, the culet is visible from the table with the naked eye in mid- and large-sized diamonds
LargeThe culet is ≈ 7.0% of the gem’s average diameter; it is usually visible with the naked eye in mid-sized diamonds
Very LargeThis culet is ≈ 11.0% of the gem’s average diameter; it is easy to see through the table of the diamond
Extremely LargeThe culet is ≈ 15.0% of the gem’s average diameter; it is very easy to see through the table of the diamond

Diamond culets in antique cut and modern cut diamonds

The size or grade of a diamond culet can say a lot about the stone’s origins, including era and cutting technique.📣 Antique diamonds, such as Old Mine and Old European cuts, were generally cut by hand, lacking the precision of modern diamond cutting techniques. As such, vintage diamonds often have larger culets, whereas most modern diamonds have tiny culets or none at all.⚖️

Additionally, culets were originally added to diamonds to protect the stone’s integrity. The thinner the diamond’s point, the more likely it was to chip, potentially causing even more damage if ignored. Today, this type of damage is less likely, and modern technology revealed that large culets in diamonds can actually impact optimal light performance and should be eliminated when possible.✅

How does a culet impact a diamond’s appearance and value?

There are several ways a large culet can impact your diamond’s beauty. For starters, if the culet is easily visible, it can appear as a dark spot when looking through your diamond’s table. This dark blemish in Medium, Slightly Large, or larger sizes can detract from the overall appearance of your diamond and become an important thing you notice when gazing at it.

Choosing a smaller culet doesn’t always help minimize the effects either, as culet size is directly related to diamond size. So, if you opt for a large diamond, this means even a Small or Medium culet could still be noticeable with the naked eye.

A large culet also acts as a window for light, allowing the beams to escape through the bottom of the diamond. This issue prevents optimal lightplay and can impact your stone’s fire, brilliance, and scintillation. To get the best value and sparkle when it comes to diamonds, it’s best to stick with pointed or tiny culets to ensure you’ll receive a stone with maximized brilliance.💪🏻

Can I find modern cut diamonds with large culets?

You can still find modern diamonds with larger culets, but it’s becoming increasingly rare. But, why would a diamond have a large culet given current gemstone cutting technology? There are a few reasons you may find diamond culets in modern diamonds.

First, while diamond shaping technology may be cutting edge, some artisans still use poor cutting techniques. The cut may be the result of trying to cut around tricky inclusions while maintaining the stone’s weight. Furthermore, diamond cutters sometimes intentionally cut a culet facet to hide or lessen imperfect faceting and symmetry in the lower half of the stone.

You may also find large culets in diamonds of significant size and weight. We mentioned above that the larger the diamond’s girdle, the larger the culet. This same sentiment extends to the physical size of a diamond as well, as larger diamonds will have broader measurements that equate to a larger culet visible through the gem’s table.🔍

Finally, a diamond cutter may be seeking the “kozibe effect”, which is a direct result of an open culet. The kozibe effect happens when a polished culet reflects through the top facets of a diamond. Some shoppers adore this “hall of mirrors'' effect that’s usually found in antique diamonds.😊 As such, some diamond cutters still utilize this process today to produce diamonds with visible open culets for a niche audience.

Spotting a diamond culet

So how can you properly inspect the culet of a diamond that you’re looking to buy? You can always use a jeweler’s loupe to get a closer look at the stone! Inspecting a diamond’s culet may be difficult if you’re not a trained professional, but with 10x magnification, you can still view the diamond face up to know if you can actually see the culet through the table with little effort.

You can also view the grading report of any diamond you’re interested in for a better understanding of its proportions and culet size. Diamond grading reports often come with a diagram or plot of the stone so you can see how all of its angles and features line up. It should look something like this:

Diamond Culet Size in the Diagram on a Diamond Report
GIA Report: 7413834600

If you’d rather not inspect every diamond’s culet, try using filters during your search to look at diamonds that fit your criteria. For instance, at Blue Nile, you can actually filter diamonds by culet size! Just open the “More Filters” tab and select “Add a Column” under the culet category to include this feature in your search results.

Culet Column in Blue Nile’s Diamond Search

Once the column appears, you can use the arrow at the top of the column to sort from smallest to largest diamond culets. 👉🏻Bonus tip: it’s best to complete your search in the “List” view so you can see all of the specs you’re filtering for!

If you’re shopping with a trusted jeweler (and we hope you are!), you can also seek their opinion regarding any diamonds you’re looking to buy. A jeweler can give you more insight regarding the size and visibility of the culet relative to the diamond’s overall appeal, value, and more.

Which culet grade should I choose?

There is no straightforward answer regarding which culet you should choose. In reality, you should take a holistic approach to diamond buying and assess a combination of factors, like budget, personal preference, and—most importantly—the diamond’s overall cut grade.

Culet size is only one criterion used to determine a diamond’s final cut grade, and diamond grading is a “big picture” process.🖼️ Most culets in modern diamonds are graded as Small to None, but even an Ideal or Excellent cut diamond can have a Medium or Slightly Large culet. Weight also plays a role here, as small carat diamonds of high cut quality often minimize the effects of a culet, meaning this category is less critical.

In the end, it’s important to understand what YOU are seeking in a diamond and inspect each stone closely to determine which one best fits your desired appeal and budget. We’ve actually created buying guides for .5, 1, 1.5, and 2-carat diamonds, so be sure to take a look at those for more tips and tricks for finding the perfect diamond!

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