Diamond Culet: Understanding Why This Tiny Facet Matters

Diamond buyers ponder the four Cs – cut, clarity, color, and carat weight – when searching for the perfect stone. But did you know that most diamonds have an additional, small facet on the bottom tip, known as the culet?

Though often overlooked, this tiny feature can impact a diamond’s appearance and structural integrity. Read on to learn what exactly the culet is, why it’s important in diamond grading, and how to shop for a stone with an ideal culet.

What Is the Diamond Culet?

The culet (pronounced kyoo-let) is the small, flat facet precisely cut onto the bottom tip or point of a diamond. Located underneath the pavilion main facets, it is parallel to the diamond’s table facet, the largest flat facet on top. Essentially, the culet serves as a protective base at the vulnerable lower point of the stone.

Definition: The diamond culet refers to the small facet at the bottom of a diamond. It can range from being very small (pointed) to larger (blunt). The purpose of the culet is to protect the tip of the diamond and prevent it from chipping.

On brilliant-cut diamonds, which have 57 or 58 facets, the tiny culet is considered the 58th facet. However other diamond cuts, like step cuts, do not always have a culet facet. In general, this facet is so small it may be challenging to see with the naked eye, especially on diamonds set in jewelry. But gemologists always view it under magnification when grading cut quality.

Why Is the Diamond Culet Important?

Though minute in size, the culet has significance in three main areas:

Protecting the Diamond Tip

First and foremost, the culet safeguards the diamond’s pointed tip, which is a vulnerable area. Diamonds have four directional cleavage planes along which they may break if struck with concentrated force. Without a culet, the pressure and possible impact occurring under normal wear is focused on a single sharp point, increasing the risk of chipping or cleaving. The culet helps distribute that pressure.

Cut Quality and Light Performance

The culet also impacts how well the diamond is cut and how it performs with light. Along with features like crown height and pavilion depth, culet size contributes to the diamond’s overall cut grade. Stones graded Ideal or Excellent should have a very small or no culet at all. Though counterintuitive, the absence of a culet can allow the maximum amount of light return through the crown. Larger culets may compromise cut quality by causing light leakage, degrading symmetry, or showing inclusions.

Diamond Appearance

Lastly, this small facet can influence the visual look of the diamond, similar to the girdle thickness. Even though it lies on the underside, the culet affects the stone’s face-up appearance. A diamond graded with a large culet may show darkness or dullness through the table facet. As the culet size increases, appeal and value decrease for many buyers.

The Diamond Cut and Culet

To fully comprehend the role of the culet, it helps to understand some basics around diamond cuts.

Diamond Cuts

The round brilliant is by far the most popular and traditional diamond shape, making up over 75% of diamonds sold today. This 57-facet cut has a culet, along with star and bezel facets on the crown, and pavilion mains and lower girdle facets on the bottom.

Other less common shapes like cushion, oval, emerald, and Asscher also typically have culets when cut in the brilliant style. These shapes showcase the complexity of a brilliant’s facet pattern.

Conversely, step cuts like the baguette, emerald, and Asscher do not always feature a culet. These linear cuts have large, four-sided facets that run parallel to the girdle, resembling steps. The pointed tip is part of the pavilion main facets.

Culet Size

On brilliant diamonds, the culet is quite small, though its actual dimensions can vary:

  • Diameter: Ranges from about 0.5% to 2% that of the total diamond diameter. A 1 carat round diamond may have a culet diameter of 0.2 to 0.5mm.
  • Visibility: It is rarely visible to the naked eye, even under magnification. A 10x loupe is usually required to view it clearly.

When grading, gemologists categorize the culet based on visibility and percentages:

  • None: No culet facet is present. Also referred to as pointed.
  • Very small: Barely visible, less than 0.5% of diameter. Preferred size for cut grades.
  • Small: Visible under 10x, 0.5% to 1% of diameter.
  • Medium: Visible under 10x, 1% to 2% of diameter.
  • Slightly large/Large: Visible unmagnified, greater than 2% of diameter.

Diamonds with large, visible culets are quite rare. Most will have smaller culets that require magnification to view and properly assess.

The Culet and Cut Grading

For diamonds to achieve the top cut grades of Excellent or Ideal, they must meet strict technical standards for factors like crown height, pavilion depth, table size, girdle thickness, and culet size.

Graders prefer a very small or no culet for Excellent/Ideal cut diamonds. Though counterintuitive, the absence of a culet can allow more light return, while larger culets permit leakage and degrade cut quality. The goal is symmetry and maximum brightness.

As the culet increases in size, it can begin to obstruct light refraction through the diamond’s point, causing darker areas under the table facet. This not only reduces brilliance but lowers the symmetry grades on a diamond’s certificate.

Pointed Tip vs. Flat Culet

In the past, diamonds were often cut deliberately with pointed tips, rather than flat culets. However, most diamonds today have a flat, polished culet instead. There are a few reasons behind this change.

First, pointed tips concentrate all pressure on that single vulnerable point of the diamond. Without a flat facet there to distribute impact, chips and cleaving risks heighten when setting and wearing the diamond.

Secondly, pointed tips allow greater light leakage out of the diamond’s bottom. This excess loss of return through the tip lowers brilliance and brightness. Flat culets help reflect more light back up into the stone.

Lastly, as consumer tastes and quality standards rose, the diamond cutting industry moved toward maximizing symmetry and sparkle. Large, visible culets and dark, bulging points faded as ideal traits. Well-cut culets became the norm.

Evaluating a Diamond’s Culet

When shopping for a diamond, either loose or certified, having some techniques to examine and judge the culet will help you identify stones with ideal facets.

Viewing the Culet

The culet can be tricky to see, especially on loose diamonds or stones upside down in unset jewelry. Here are some tips:

  • Use a 10x loupe or jeweler’s loupe for inspection. Higher magnifications like 20x may be needed for very small culets. Graduated eye loupes that range from 10x to 30x are ideal for first assessing size.
  • Make sure to view it with the diamond inverted, pavilion side up. Eye loupes often clip onto eyeglasses, leaving your hands free to hold the gem.
  • Rotate the diamond to locate the culet and identify it correctly. Sometimes it is not visible until you find the proper orientation to the eye.
  • Look for bright reflection and color flashes, a clue you have the culet facet in view.
  • Adjust your lighting source or angle as needed. Bright fixed lights aimed straight down can make the culet easier to observe.

Grading the Culet

Once you have the culet in clear sight, judge its size and polish. Use these guidelines:

  • None: A complete absence of a culet should raise concerns, as this removes protection from the point and can indicate lower standards. Reputable cutters should not intentionally produce diamonds with no culet.
  • Very Small: An ideal culet is just barely visible under magnification. This tiny facet protects the tip without compromising cut quality or appearance. Stick within .5% of the diameter.
  • Small to Large: Enlarged, visible culets negatively impact light performance and appeal. They can potentially lower value.
  • Polish: The culet should feature expert faceting and polish just like any other diamond facet. Dullness or poor workmanship is unacceptable.

Diamond Certification and the Culet

For certified diamonds that have been graded by gemological institutes like GIA or AGS, the culet size will be clearly listed on the accompanying report or certificate. There is no need to guess or personally assess the culet yourself. You can trust that a reputable third party has evaluated and classified it.

Certificates provide assurance that the culet meets quality benchmarks. Jewelers highly recommend selecting certified diamonds, especially for important purchases. Uncertified diamonds pose risks of imprecise or inconsistent grading.

Impacts on Diamond Pricing

An ideal culet can raise a diamond’s overall appeal and value in the marketplace. Here are factors to consider:

  • Well-cut culets show skill and standards: Diamonds precisely cut with very small or no culets command higher prices and are more desirable. They exhibit quality workmanship.
  • Larger culets can reduce prices: As culet size increases, diamonds begin losing their brilliance and allure for buyers. Discounts may apply.
  • A missing culet raises concerns: Diamonds lacking a culet altogether should not cost more. In fact, the point’s vulnerability may warrant negotiations or rejection of the stone.
  • Certified diamonds command premiums: Paying the premium cost for graded, certified diamonds with ideal culets provides assurance and protection compared to uncertified options.

Finding Diamonds With the Ideal Culet

Where and how you purchase your diamond impacts options for verifying the culet. Here are shopping tips:

Local jewelers and diamond retailers are great resources, especially if building custom pieces. Ask questions like:

  • What are your standards for culet quality? Only buy from those with high benchmarks.
  • Do you have diamonds with a range of culet sizes to view? Examining variations will sharpen your eye.
  • For custom designs, will you show me diamonds with different culets to select my preference? Reputable retailers happily will.

Buying certified diamonds online offers convenience and competitive prices. Use these best practices:

  • Filter search results by specific culet size, especially if you prefer very small or none. Not all sites offer this capability though.
  • Read the diamond certificates to identify culet classifications. Rely on 3rd party assessments.
  • Exercise return policies if you have received diamonds that have larger culets than expected. Inspect carefully.

Key Takeways

The culet plays a role in grading, appearance, and durability.

As a professional gemologist, I recommend considering a culet grade of “None” or “Very Small”.

Diamonds with culets graded as “none” or “very small” are often preferred because they have minimal impact on the diamond’s appearance and light performance. These diamonds may be slightly more desirable and, consequently, may command slightly higher prices compared to diamonds with larger or more visible culets.

Smaller culet sizes are often preferred for their potential to enhance brilliance and aesthetics. However, the overall quality and appearance of a diamond depend on multiple factors, not just culet alone.

Carl A. Jones, GIA GG

Carl A. Jones is a GIA Graduate Gemologist with over 20 years of experience in the diamond industry. He is an independent jewelry appraiser. He specializes in determining the value of diamonds and advising consumers on how to buy quality diamond jewelry.

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