Diamond Cut Quality: Everything You Need To Know
If you take one thing away from us, make it what’s on this page. 15 minutes spent reading the information below could be the best time spent in all of your diamond research. Consider a bookmark.
Unlike color and clarity, where the highest grades are rare, more than 60% of round brilliants receive the “Excellent” diamond cut grade, despite having visible character and quality differences.
When shopping on the internet, it’s especially important to research cut quality because this one “C” often has a visibly positive or negative influence on the other Cs, making it by far the most important.
Before going on: Check out the PriceScope Diamond Buying Guide
Diamond cut quality assesses craftsmanship and basic light behavior (for round cuts). However, unlike the other Cs, diamond laboratories disagree on how cut should be graded.
The Wild West of Cs
Unlike color and clarity, where the highest grades are rare, over 60% of round brilliant diamonds receive the highest cut grade of “Excellent,” despite having visible character and quality differences.
|PriceScope Pointer: Only 23% of GIA Excellent round brilliants pass our patented online Holloway Cut Advisor test (HCA). Keep reading and use our HCA tool to reject “Excellent” diamonds with diamond cut performance issues.|
Also unlike color and clarity, where top-tier laboratories adhere to uniform standards, a diamond graded “Excellent” by one laboratory could be judged “Very Good” by another and “Fair” by still another. Furthermore, most labs issue no cut grade for fancy shapes.
All diamond shapes receive laboratory grades for polish, which analyzes how lustrous and unblemished the surface is – and symmetry, which judges the evenness and consistency of a diamond’s surface outline and facets.
Round Brilliant cut diamonds also receive an overall diamond cut grade – a conclusion by that laboratory about how bright or dark the diamond is: Diamonds cut with geometries too deep or too shallow may appear dark for various reasons, while diamonds with proportionate geometries successfully reflect, refract and return light to the viewer as brightness, fire, sparkle and contrast.
Be advised: Most diamonds are not cut with proportionate geometries because cutting deep brings more profit to diamond producers.
Diamond Cut Chart: Ray Paths
Warning: You can dive deeper and deeper into this topic – and that’s okay. You should at least break the surface and learn the limitations of grading reports. Beyond that, how far you choose to “nerd out” (and we mean that as a compliment) is up to you.
Not everyone needs to become a diamond cut quality rocket scientist, but if you want to be fully confident about the cut quality of diamonds you’re considering the methods below have been proven – again and again.
Choose the path that’s right for YOU
If you want to stay dry, just click back to PriceScope 101 and follow the shortcuts. But if you want to learn more about diamond cut in one sitting than most diamond buyers will ever know just keep reading. You might become the person your friends all turn-to for diamond advice.
We’re not kidding.
The inconvenient truth is that most diamonds are not cut well because carat weight is the number one driver of price. That motivates diamond cutters to keep the most possible weight in the diamond:
Diamond Cut Chart: Planning
The typical rough diamond octahedron produces two finished diamonds. The primary stone has the most value. Diamond producers will use angles as close to the rough outline as possible (circa 45 degrees) which can still earn a favorable grade like “Excellent” or “Ideal.” However, those angle combinations fall outside optimal proportional geometry, resulting in darker, less lively diamond cut quality.
Is that “Weight over Beauty?”
Yes. Most diamonds are produced for weight over beauty. This is possible because most laboratories maintain very loose diamond cut grading standards. For example, over 60% of round diamonds passing through GIA receive their top cut grade of Excellent, despite being produced for weight over beauty. It’s not an exaggeration to say most diamond shoppers have probably never seen a diamond cut to have the best brightness and sparkle possible.
Bottom Line: Cut quality has the most influence on diamond beauty but is by far the most variable C, and the majority of diamonds are produced for weight over beauty.
|PriceScope Pointer: For shapes other than round see our page on fancy shape diamond assessment.|
Believe it or not, YES.
You’ll be happy to know PriceScope is considered a real pain-in-the-neck by many diamond sellers.
This is because our community specializes in diamond cut quality knowledge. We have more diamond enthusiasts with more experience over a wider range of diamond cut quality than any other online resource. With a community made of of members who are consumers like you, you can be sure they have your best interest in mind.
Three Common Round Brilliant Subsets*
The PriceScope Community frequently refers to three subsets or “makes” of round brilliant diamonds.
- Steep Deep
- PriceScope Ideal
- Super Ideal
*A few other subsets exist, but are far less frequent. We will detail them on a separate page.
The three examples below are hypothetically polished from the same starting rough crystal (the dark blue outline). They have identical color and clarity, and all received the “Excellent” cut grade.
The different final weights are due to different cut quality goals. Remember, the more cut quality attention a diamond is given, the more weight is polished away, and the smaller the finished diamond becomes.
The Steep Deep (hypothetical final weight 1.15 ct)
This subset is most abundant by far. Wide (steep deep) cutting angles are used by producers to maximize yield, increasing the diamond’s final weight. Those wide angles cause light return issues because rays entering the diamond leak out of the bottom, instead of reflecting and returning to the viewer’s eyes. When removed from bright lights, steep deep diamonds quickly go dark and look physically smaller than they should.
> Identifying Steep Deep diamonds
- Many steep deep diamonds can earn the GIA Excellent cut grade
- Use the Holloway Cut Advisor (HCA) to identify and reject diamonds with light return issues
- An Ideal-Scope image will reveal light return issues in any round brilliant diamond
The PriceScope Ideal (hypothetical final weight 1.06 ct)
Only 20% of all round brilliant diamonds graded ‘Excellent’ or ‘Ideal’ will qualify as PriceScope Ideals (PriceScope estimate). They are cut with proportionate, complementary angles which successfully reflect and return light back to the viewer’s eyes as brightness, fire, contrast, and sparkle (some slightly emphasize brightness over fire, or vice-versa, depending on specifics). When removed from bright lights, they remain brilliant and lively. Diamonds in this subset tend to finish around 3-7% smaller than they would have, if cut with steep deep angles.
> Identifying PriceScope Ideal diamonds
- Use the Holloway Cut Advisor (HCA) to identify diamonds with top light return
- An Ideal-Scope image can verify top light return in any round brilliant diamond
- PriceScope Ideal diamonds will earn the highest performance grade at any top-tier laboratory
PriceScope Ideal (equivalent version)
The advice above has successfully served thousands of PriceScope readers, but taste varies. Some of our members prefer different visual character. Some prefer a different shape entirely. In that spirit, a PriceScope Ideal can be any aesthetically pleasing diamond you see and personally love.
The Super Ideal (hypothetical final weight 1.00 ct)
Only 3-5% of all round brilliant diamonds graded ‘Excellent’ or ‘Ideal’ fall into the Super Ideal subset (PriceScope estimate), making them extremely rare. They are cut within a small range of acknowledged “ideal” proportions which promote balanced brightness, fire, sparkle, and contrast. Beyond those basic proportions, their internal reflections are further fine-tuned to display 3D optical precision (aka Hearts & Arrows), proven in a specialized viewer. Top Super Ideal diamonds are not casually or accidentally made. They finish around 5-13% smaller than they would have, if cut with steep deep angles.
> Identifying Super Ideal diamonds
- Super Ideal diamonds are frequently sent to the AGS for strict light performance cut-grading
- An AGS Platinum Light Performance report can confirm “Ideal” light performance
- Hearts & Arrows images (real, not computer generated) can confirm 3D optical precision
To identify Super Ideal diamonds graded by other laboratories, use the Holloway Cut Advisor (HCA) first, then ask for an Ideal-Scope image to verify top light return. For any diamond sold as Super Ideal, actual Hearts & Arrows images should be provided.
See all round diamonds with Hearts & Arrows photos, 1.00-1.19 carats with GHI color and VS1-VS2 clarity.
The Premium Perception
Does improved performance come with a pricing premium? Remember that all three examples below had the same raw material cost. All three earned the “Excellent” cut grade. On paper the only difference is carat-weight.
For example, if the raw crystal had been H color, VS1 clarity (according to market pricing, Feb 2021) and the three examples were priced with the same retail markup:
- 1.15 ct H VS1 $8,000
- 1.06 ct H VS1 $8,000
- 1.00 ct H VS1 $8,400
To a casual shopper, the 1.06, and the 1.00 especially, appear to command premiums over the 1.15, but that’s not quite true. Remember, the 1.00 and 1.06 could also have finished at 1.15, but the cutter chose to keep polishing to improve brightness and optical quality.
In that sense, instead of a premium for positive polishing, there is a discount for the deep.
The “Deep Discount”
Steep deep diamonds are most abundant on the market because, lacking this education, casual shoppers assume they are getting more carat weight for the money. Most jewelry stores do not carry diamonds in the PriceScope Ideal or Super Ideal subset, so you may never have seen one in person before.
See eye clean PriceScope Ideal round diamonds, already thoroughly vetted by our PriceScope sellers.
Successful online sellers like our recommended PriceScope vendors, have methods of reliably classifying and communicating diamond cut quality in a number of ways, and back it up by offering liberal inspection periods and free returns.
- Start with diamond grading reports: Diamonds over 0.25ct should come with a full report (or certificate) issued by a gemological laboratory. Diamond color and clarity grading are subjective, so tolerances among labs vary – even between a single lab’s various locations – but the accepted standard among reputable institutions is +/- one grade.
|PriceScope Pointer GIA, AGS, IGI and GCAL all grade loose diamonds with strict, reliable standards. Read more about these laboratories on our diamond grading page.|
- Look for seller-provided photos and videos: First things first. Camera and monitor settings make diamonds look different screen to screen, so while you can’t make nuanced decisions, videos and images are useful. And when a seller’s in-house images are consistently made, in one setup, then head-to-head comparisons within that seller’s inventory are practical.
- Look for standardized imaging: Grading laboratories are now offering imaging services with calibrated white-balance, filtered lighting, and fixed focal-depth. Videos and images of diamonds made in these standardized conditions may be compared head-to-head, between sellers, and are a sales-neutral extension of independent grading.
- Ask the seller directly: If you have questions beyond what a diamond grading report and supplemental videos and images can communicate, pick up the phone, chat, or email and get in touch with the vendor. It’s in their best interest to communicate transparently with you. After all, they don’t want the expense of shipping a diamond, only to have it returned on their dime as well.
- Get quick answers to any question now: Ask our community of unbiased independent helpers.
|Ready to find your diamond?|
Intermediate Diamond Cut Quality
If, instead of diamond cut quality, we are trying to predict the looks and performance of an athlete:
- Proportions Measurements are like having the athlete’s weight and height.
- The Holloway Cut Advisor (HCA) outlines their physique for us.
- Performance Scope Images are like seeing still photographs of the athlete in action.
- Computer modeling is like having video proof of their abilities.
- Finally, in-person viewing with helpful input from a coach, is most decisive.
The physics of light-behavior within a diamond are reliably consistent, which means proportions-measurements can be used to draw certain conclusions about diamond cut quality and likely appearance. There are eight facet groups on a round brilliant diamond: See Round Brilliant Diamond Cut Anatomy for a detailed look at all of them.
You only need four of those proportions to take the next step and use our online Holloway Cut Advisor (HCA).
- Table Size
- Total Depth
- Crown Angle
- Pavilion Angle
With those four data points, along with the diamond’s carat weight and millimeter measurements, you are ready to use the HCA.
Two of those numbers are averages of eight measurements, and there is no way to know how far the minimum and maximum measurements are “off” from that average. But at this point it’s no big deal.
Proportions measurements are terrific to use with broad predictive analysis tools. If you want to get into nuances like diamond cut consistency or 3D optical precision, we cover them below in performance scope images and computer modeling.
|PriceScope Pointer: The numbers on GIA reports are not accurate to the tenth of a degree, like those on AGS reports. The Pavilion Angle is rounded to the nearest 0.2 degrees. The Crown Angle, Star and Lower Halves are rounded to nearest 0.5 degree or 5%. This prevents extremely detailed analysis.|
The Holloway Cut Advisor (HCA) uses the key measurements of a round brilliant diamond to calculate potential light return, fire, scintillation and spread based on grading report information.
The HCA is the best rejection tool available for assessing diamond cut. Its primary use is disqualifying candidates. While doing this it also gives reliable broad predictions about light return (brightness) and spread (physical size for carat weight), as well as hypothetical conclusions about fire and scintillation using a logical basis.
The HCA score is not diamond specific. It does not take the 40 minor facets into consideration (of 57/58 on the diamond). It does not account for nuances of cut consistency or 3D optical precision, for those seeking such detailed diamond cut analysis.
The HCA is the best rejection tool available. It’s like having an “HCA radar gun” which reliably tells you what cars are speeding so you can reject them as unsafe drivers. It also identifies safe drivers but is not capable of deducing which one might be the “safest” driver.
See these popular HCA Excellent round diamonds, 1.00-1.19 carats with GHI color and VS1-VS2 clarity.
Online sellers focusing on diamond cut quality are increasingly adopting Ideal-Scope and the AGS ASET (angular spectrum evaluation theory) scope. These are two reliable methods of proving or disproving that a diamond is properly returning the light it gathers from above to the viewers’ eyes.
|PriceScope Pointer: “Hearts and Arrows” viewers are not performance scopes. Those viewers only show optical diamond cut precision: they give no indication of positive or negative light performance.|
- The Ideal-Scope looks like a pink and black shot-glass.
- The ASET scope looks similar, subbing blue for black and adding green.
Positive Light Return
- Both scopes code light coming from the highest angles their darkest color (BLACK or BLUE).
- The Ideal-Scope codes all light entering from 0 to 75 degrees as red.
- The ASET scope codes light from 0 to 45 as green and 45-75 as red.
Negative Leakage (Windowing)
- Areas of the diamond which leak light appear white in the Ideal-Scope and in backlit versions of the ASET scope. For ASET scopes without backlighting, those areas appear grey.
Superior: Diamonds cut with the best light return will show edge to edge red in both viewers. They will have symmetrical, evenly distributed contrast patterns seen as black (Ideal-Scope) or blue (ASET). The only light/white areas will be tiny symmetrical points of white at facet meet points and the girdle.
Average: Diamonds cut with average light return may have negative white/grey areas of leakage (windowing) near the center and/or at the girdle. They may show light drawn from disadvantageous low-angles (green) in ASET. Their contrast patterns, seen as black (Ideal-Scope) or blue (ASET), may not be symmetrical or evenly distributed.
Poor: Diamonds cut with poor light return will have distinctive areas of negative white/grey leakage near the center, possibly showing as circular “rings” of leakage. They often show light drawn from disadvantageous low-angles (green) in ASET, particularly along the girdle/edge of the diamond. Their contrast patterns, seen as black (Ideal-Scope) or blue (ASET), may only resolve partially and are asymmetric.
|PriceScope Pointer: Some jewelers don’t know the difference between performance scopes (which show light return behavior) and Hearts and Arrows viewers (which show optical precision but not performance). Be sure your chosen jeweler understands the difference.|
Structured lighting environments such as Ideal-Scope and ASET are the simplest but most effective way to “map” the light traveling through a diamond. Brightness, leakage, and contrast can be meaningfully assessed, especially in standardized setups.
Performance scopes images provide a motionless view of brightness, leakage, and contrast, but the benefits of diamond cut performance occur in motion, over a full range of tilt. Different setups may also influence how much or little leakage is seen.
When buying a diamond online Performance Scope Images are a tremendous help in understanding the overall quality of a diamond’s light behavior as it relates to critical components of brightness, leakage, and contrast.
Think of a diamond as a tiny geometric sculpture where every facet has a purpose. The light behavior, particularly how bright or dark that diamond will be, depends on the alignment and orientation of all facets in relation to each other.
Computer modeling diamond cut quality begins with a 3D scan created in a diamond scanning device. In this process the diamond is placed upside-down on a rotary platform, surrounded by lights. The lights turn on and the silhouette of the diamond is captured eight times as it rotates. An integrated camera measures the angles of that silhouette.
The 3D model is then imported into software designed to follow the light as it travels through the diamond, taking its total sculpture into account. This computer modeling approach is called “ray tracing.”
The AGS Light Performance Cut Grade
In 2005, the American Gem Society introduced a Light Performance Cut Grade system based on ray tracing. A diamond’s 3D scan is used to determine values for brightness, leakage, contrast, and dispersive potential. Those values determine the diamond’s performance grade on a scale of 0 (best) to 10 (worst). A computer generated image (CGI) of the diamond as it will be seen in the AGS ASET performance scope is also calculated and imprinted on AGS Platinum Reports.
This is the world’s only diamond-specific cut grading system to date. In other words, only AGS analyzes each specific diamond sculpture in its entirety, tracing 40,000 rays of light with computer software. Other labs use a handful of average measurements, correlate them with charts and pencil in a diamond cut grade.
Dual and Triple Light Maps
AGS offers “dual light map” and “triple light map” certificates, as seen below. In these cases an ASET image is rendered for the bottom of the diamond. The only purpose of that rendering is to provide an impression of 3D optical precision, also known as “Hearts and Arrows.” While the 3D scan computer generated images can be very representative, a diamond’s optical precision is best judged with actual photos or in-person viewing.
You can read more about optical precision on our Hearts and Arrows Diamonds page.
DiamCalc is a system for polished gemstone modeling and design. The software can be used to generate a variety of photorealistic diamond images and videos, including performance scope (i.e. Ideal-Scope, ASET) and optical precision scope (i.e. Hearts and Arrows) simulations. Professional versions of DiamCalc feature a ray tracing engine which may be used to design theoretical diamonds, in the same manner as architects use CAD to design and assess buildings prior to construction.
|PriceScope Pointer: Before using computer generated images (CGI) for analysis it’s critical to know whether the images were generated by manual input or from a mechanical 3D scan of the diamond.|
Manual Input (not useful for CGI)
Computer-generated images (CGI) can be produced by manually entering numbers from a grading report into the software. When this methodology is not disclosed it’s misleading. When broad average numbers are entered the software simulates perfect 3D optical precision for the missing facets (which doesn’t exist in nature) and produces images based on a theoretically perfect, unrealistic diamond wireframe.
Note: Manual input of grading report averages can be useful for broad conclusions regarding overall light return versus light leakage. Such use should be clearly disclosed as a non diamond-specific estimate.
3D Scan (uses actual mechanical scan)
Diamond 3D scans are very useful for light performance assessment with ray tracing, as well as producing diamond-specific Ideal-Scope and ASET CGI which are representative. Since all facets have been scanned in three dimensions the projections of light-behavior within the diamond are accurate.
Hearts and Arrows Analysis: Hearts and arrows images generated with a 3D scan may be very close to the diamond’s actual hearts and arrows but are not as decisive as actual photos or in-person viewing. You can read more about optical precision on our Hearts and Arrows Diamonds page.
Computer Modeling Summary
Because computer generated images have the appearance of actual photos, it is important to verify with the seller if the imagery they are providing is actual photography of the diamond, or CGI. If the images are CGI, verify that the seller secured a mechanical 3D scan of the actual diamond.
|PriceScope Pointer: Whether intentional or by accident, some diamond sellers provide Ideal-Scope, ASET and Hearts and Arrows simulations from manual input CGI. Those images do not represent the subject diamond and give a false positive impression. Be sure a mechanical 3D scan was used. You might also ask the seller to send you the 3D scan. Common file formats are .SRN .STL .DMC .ASC and DXF.|
Computer modeling is the most sophisticated method of clinical diamond cut assessment. When imported, 3D diamond scans can reliably and accurately be used to place diamond cut quality in a performance category such as GIA Excellent or AGS Ideal, and to identify shape subsets such as Super Ideal, PriceScope Ideal and Steep-Deep.
3D scans of gemstones are created without any contact. The diamond is placed on a rotary platform surrounded by lights. The lights turn on and the diamond’s silhouette is captured eight times as it rotates. An integrated camera measures the angles of that silhouette. Device makers acknowledge potential linear error of ± 10 microns and angular error of ± 0.1 degrees per measurement.
With a high-quality 3D scan, much can be determined about overall diamond cut performance. For extremely nuanced analysis regarding matters like optical precision, or hearts and arrows, it’s best to use actual images or view the diamond in an optical precision scope in person.
Diamonds are traditionally shown to prospective buyers in a single location, usually under spotlights which make all diamonds look good.
It’s important to remember that diamond cut quality is all about how a diamond looks as it travels through the world’s infinite panoramas of illumination. Diamond beauty is dependent on the specific diamond, the specific environment, the specific viewer and – most of all – the light environment.
Ensure Environmental Variety
If the three “Ls” of real estate are “Location, Location, Location”, the three “Ls” of Cut Quality are Lighting, Lighting, Lighting.
Instructions for Thorough In-Person Viewing
A. Setting Up The Diamonds
- If comparing 1 diamond, use tweezers or a temporary mounting
- If comparing 2-3 diamonds, place them in temporary mountings
- If comparing more than 3 place them side by side on a white diamond-viewing tray
- Be prepared to return, with your favorite two in temporary mountings or on your skin
B. Lighting Definitions
- Spotlighting: Small intense lights overhead. These are seen in every jewelry showroom and most household bathrooms (facilitates brightness-dispersion-scintillation)
- Natural Lighting: Large window or porch area where sunlight/daylight is visible (facilitates brightness-dispersion)
- Diffused Lighting: Fluorescent tubes or diffused indirect light, as in a school classroom or office (facilitates brightness)
- Low Lighting: Darkened room, corner, or other areas where no overhead light exists (reveals leakage)
- Filtered Lighting: Outside area in sunlight under a tree with leaves moving (facilitates scintillation)
C. Prepare Yourself and Other Viewers
- Is someone wearing eyeglasses? They will perceive dispersion and scintillation differently.
- Are there observers over 40? Presbyopia has often set-in, so go ahead and keep the reading glasses on if they want to get close.
- Are there observers under 21? They may detect nuances others do not, as they can focus as close-distance.
- Is someone wearing a yellow or brown shirt? Diamonds reflect their surroundings. They will take on that color appearance in general and in their performance qualities.
Take the tour!
Stop 1: Spotlighting:
Start under overhead spotlights as you would see the diamonds in a jewelry store. Compare the diamonds at 18 inches. Hold them still, then move them slowly side to side. Then move them rapidly. Look for overall brightness (white and colored light). Ask which has more white sparkle (isolate glare), which has more colored sparkle, which seems more vivid (more intensity in brightness and darker contrast). Does one have more rapid/small sparkle while another has more broad/large sparkle?
Now move them from arm’s length slowly to very close up. Does one get darker as it comes closer? Do they both remain as-bright? Do they both remain as vivid in brightness and contrast? If you’re inclined to take notes, by all means do, since these comparisons will be made in a few different lighting conditions.
Stop 2: Natural Daylight
Whether outside or near a window, stand with daylight at your back so the diamonds are illuminated by natural, completely outdoor lighting. Go through the same comparative exercises listed above. If it’s a cloudy day you can expect to see far less fire. If it’s a sunny day the diamonds may actually look somewhat dark inside, but the colored flashes should be electric.
Stop 3: Diffused Lighting
If you don’t have specific classroom or office-style lighting you can diffuse overhead lights with a pillowcase or sheet. There should be no spotlights or direct lighting of any kind in this environment. These conditions resemble the diffused northern daylight of a diamond bourse. Much like a cloudy day, you will see little or no fire here. Go through all of the same comparisons, this time focusing on how bright the comparative diamonds remain, and how symmetrical the contest patterns are.
Stop 4, Low Lighting:
This can be done under your desk or kitchen counter. No direct light at all is preferred. In a pinch you can cup one hand over the other that is holding the diamond and see how it appears when gathering only the most limited light. A very important test in this condition is to see if either diamond “gets smaller” than the other, or if they both retain their side-to-side size appearance.
A diamond that seems to “get smaller” may not be returning light from edge-to-edge as the finest cut diamonds will – and one where you literally see through the center is leaking light through the pavilion.
Stop 5, Filtered Lighting:
Many diamond professionals have discovered the joy of viewing a well-cut diamond on a bright day, but standing underneath a tree where the leaves are moving and permitting sunlight to filter down to the diamond.
Why is this such a great environment? Ambient sunlight reaches down to the horizon, promoting edge to edge brightness, while the leaves break up the cascading sunlight, creating abundant scintillation events. Meanwhile, your pupils have contracted (because your brain registers the sunlight) and in that state they clip abundant dispersive fans, causing your optic nerve to perceive far more colored flashes than you do in other illumination scenarios.
It should go without saying but be sure the diamond is completely secure and will not fall or pop out of the tweezers if you choose to take it outside.
Get quick answers to any question now: Ask our community of unbiased independent helpers.
|Ready to find your diamond?|