Jewelry
Beyond the 4 Cs: How Gemstone Clarity Is Actually Graded
October 17, 2026
Two diamonds with the same clarity grade can look completely different. Here is how gemologists actually grade clarity and why the letter grade is only part of the story.
Most people shopping for a diamond learn about the 4 Cs. Cut, color, carat weight, and clarity. The clarity part seems simple enough at first glance. A jeweler hands you a certificate with a letter grade, and that tells you how clean the stone is. But if you have ever looked at two diamonds with the exact same clarity grade and wondered why one looks sparkling clear while the other seems a bit cloudy, you have already discovered the secret about clarity grading. The grade is just the beginning of the story.
The system is thorough and standardized, but it is also deeply nuanced. Understanding how gemologists actually arrive at that grade can change the way you look at every diamond you encounter.
The 11 Steps of the Clarity Scale
The Gemological Institute of America, or GIA, created the clarity scale that most of the jewelry industry uses today. It has 11 specific grades, running from the absolute cleanest stones down to those with the most visible marks.
At the very top is Flawless, written as FL. A flawless diamond has no internal features and no surface blemishes visible at 10x magnification. Just below that is Internally Flawless, or IF. These stones have tiny surface blemishes but no internal characteristics. From there, the scale moves through Very Very Slightly Included grades, then Very Slightly Included, then Slightly Included, and finally Included.
Flawless diamonds are extraordinarily rare. A jeweler can spend an entire career in the industry without ever seeing one. Because they are so scarce, they carry a significant premium. The vast majority of diamonds sold in stores fall in the middle of the scale. These are stones with tiny inclusions that are completely invisible to the naked eye but can be seen by a trained gemologist looking through a magnifier.
Under the Loupe: What Gemologists Actually See
Clarity grading is performed by a skilled gemologist looking down through the top of the stone at 10x magnification. The standard tool for this is a jeweler's loupe, a small handheld magnifying lens. A gemologist examines the stone carefully and notes every internal feature and every surface irregularity visible at that power.
Inclusions are the internal features trapped inside a diamond as it forms deep in the earth. These can take many forms. A pinpoint is a tiny crystal that looks like a speck of dust. A feather is a small crack inside the stone. Sometimes a diamond even traps a smaller crystal of a different mineral as it grows.
Blemishes are the external surface irregularities. These include scratches, nicks, and small chips. The gemologist considers all of these features when assigning a grade.
The 10x standard matters because it gives the entire industry a shared baseline. A diamond might look perfectly clean to your unaided eye, but the gemologist is looking at a level of detail you simply cannot see. Everything visible at 10x becomes part of the clarity picture.
The Five Factors Behind the Grade
Here is where clarity grading gets interesting. A gemologist does not simply count the number of marks and assign a grade. Five key factors work together to determine where a stone falls on the scale. They are size, number, position, nature, and color or relief.
Size and number are straightforward. A larger inclusion has more impact than a smaller one, and several inclusions have more impact than a single one. Position, however, can be decisive. An inclusion located directly under the table, which is the large flat facet on the top of the diamond, has a significant impact on the clarity grade. The same inclusion tucked away near a prong where the setting meets the stone has far less impact. A mark hidden near the edge simply draws less attention.
The nature of the inclusion matters too. A benign pinpoint is just a small internal crystal. It has no effect on the durability of the stone. A feather, which is essentially an internal crack, can lower the grade and may potentially threaten the diamond's durability if it reaches the surface.
Color and relief refer to how much the inclusion stands out against the diamond. A dark inclusion is easier to see and has more impact than a clear or white one. A gemologist weighs all five of these factors together for every stone.
Why Two SI2 Diamonds Can Look Completely Different
This is the part that often surprises people. Two diamonds can carry the exact same clarity grade and look completely different to the naked eye. Understanding why requires looking at how those five factors interact.
Take two diamonds both graded SI2, which stands for Slightly Included. The inclusions in an SI2 stone are quickly noticeable at 10x magnification. They may also be visible to the naked eye. One of these diamonds might have several small dark inclusions clustered right under the table. That stone would show visible marks when you look at it from the top, and the inclusions might affect how light travels through the diamond, reducing its sparkle.
The other SI2 diamond might have its inclusions positioned off to the side, where the prongs of the setting can hide them. This stone could be what the industry calls eye-clean. No inclusions are visible to the unaided eye when you look at the stone face-up. Both stones have the same grade, but they look entirely different.
The industry has a specific consensus for what eye-clean means. No inclusions are visible to the unaided eye when the stone is viewed face-up in daylight-equivalent or fluorescent lighting at a distance of 6 to 12 inches using 20/20 vision. A grading certificate tells you the clarity grade, but it does not tell you whether the stone meets that eye-clean standard. That is something you can only determine by looking at the actual diamond.
Inclusions as Fingerprints
There is a fascinating upside to inclusions. They help gemologists separate natural diamonds from laboratory-grown synthetics and from simulants like cubic zirconia. The specific types and patterns of inclusions found in natural diamonds tell a story about their formation deep in the earth over millions of years.
Inclusions also serve as a kind of fingerprint. No two natural diamonds have exactly the same inclusions. A gemologist can use the size, type, and position of these internal features to identify an individual stone. This is why grading reports often include a plot, which is a diagram of the diamond showing the location of each clarity characteristic. The International Gemological Institute, or IGI, plots these characteristics on their reports using red marks for internal features and green marks for external blemishes.
For anyone shopping for estate jewelry or secondhand pieces, these plots are valuable. They let you match a diamond to its grading report and confirm that the stone in the setting is the one described on the paper.
Reading Between the Lines
Clarity is about more than a single letter on a certificate. The grade gives you a reliable starting point, a standardized way to compare stones. The five factors of size, number, position, nature, and color or relief tell you what the gemologist saw and how they weighed it.
The next time you look at a diamond grading report, remember that the letter grade is a summary of a detailed story. Two stones can share a grade and still offer very different experiences to the person wearing them. The real beauty of a diamond, and its true clarity, reveals itself when you look at the stone itself.