A prominent characteristic in a diamond is the single inclusion or blemish that has the biggest influence on that stone’s clarity grade. When a gemological lab evaluates a diamond, it identifies all the internal and surface features, then determines which one matters most. That feature is the prominent characteristic, sometimes called the “grade maker” or “grade-setting inclusion,” and it’s listed first in the Key to Symbols section of a grading report.
How Labs Identify the Grade-Setting Inclusion
Every diamond contains some combination of internal features (inclusions) and surface irregularities (blemishes). The Gemological Institute of America groups these together as “clarity characteristics.” To decide which one earns the title of prominent characteristic, graders evaluate five factors: size, number, position, nature, and color or relief.
No single factor always wins. The relative importance shifts from diamond to diamond. A tiny crystal directly under the table facet (the flat top of the diamond) can hurt the clarity grade more than a larger inclusion tucked off to the side, because position matters more in that scenario. In another stone, a dark inclusion might stand out against the diamond’s transparency, making color or relief the deciding factor. Graders weigh all five factors together and judge which characteristic, on balance, has the greatest impact.
Reading It on a Grading Report
On a GIA grading report, the clarity plot diagrams where each inclusion and blemish sits inside the stone. Next to the plot is the Key to Symbols, a list of every characteristic the grader noted. The order of that list is not random. Characteristics are listed in order of their importance to the clarity grade, so the first item is your prominent characteristic. The only exception is a laser drill hole, which gets listed first for disclosure purposes regardless of its role in grading.
After the grade-setting inclusions, the report lists other inclusions, then naturals (rough diamond surface left on the finished stone), and finally extra facets. If you want to quickly understand why your diamond received a particular clarity grade, look at the first entry in that list and find it on the plot diagram. That’s the feature the grader decided mattered most.
Other labs like IGI follow a similar approach but sometimes provide less detail in their clarity plots. The level of specificity can vary, so reports from different labs may not break down the listing order as clearly.
Common Types of Prominent Characteristics
The nature of the grade-setting inclusion tells you what kind of feature it is. Some of the most common types include:
- Crystal: A tiny mineral trapped inside the diamond during formation. These can be white, dark, or even colored, and dark crystals tend to hurt the grade more because they’re easier to see.
- Feather: A small fracture inside the stone that can look like a wispy, feather-shaped line. Feathers are graded harshly by labs because of the theoretical risk they pose to durability, but in practice a diamond that survived formation, mining, and cutting is unlikely to break along a feather under normal wear.
- Cloud: A cluster of very tiny inclusions grouped together. Individually they’d be invisible, but collectively they can create a hazy area.
- Needle: A thin, elongated crystal that appears as a fine line under magnification.
- Knot: A crystal inclusion that reaches the diamond’s surface, sometimes visible as a raised bump on a facet.
The type matters for more than just grading. A feather that reaches the surface of the diamond, extends to the girdle edge, or connects to other feathers near the surface could present a durability concern, especially if the stone takes a direct blow. But a feather that stays entirely internal generally poses no structural risk. Diamonds set in pendants or earrings face very little impact, so even a surface-reaching feather is less worrisome in those settings. For rings, it’s worth checking whether the prominent feather is in a vulnerable position.
How It Affects What You See
Whether the prominent characteristic is visible to the naked eye depends on the clarity grade. At VS1, roughly 95% of diamonds appear completely clean without magnification. At VS2, about 85% look eye-clean under normal viewing conditions. Once you drop into the SI1 and SI2 range, the prominent characteristic becomes increasingly likely to be something you can spot, particularly if it’s dark, centrally located, or large.
Position plays an outsized role in visibility. An inclusion directly under the table facet is essentially looking straight back at you, while the same inclusion near the pavilion (the lower half of the diamond) may be masked by the stone’s internal reflections. A prominent characteristic off to the side can also be hidden by the setting, especially in prong or bezel designs that cover the edges of the stone.
This is why two diamonds with the same clarity grade can look very different. One might have a prominent dark crystal right under the table, while the other has a prominent feather near the girdle that’s essentially invisible face-up. The grade is the same, but the buying decision shouldn’t be.
What This Means When Shopping
Understanding the prominent characteristic helps you shop smarter because the clarity grade alone doesn’t tell the full story. Two SI1 diamonds are not interchangeable. One might have a white feather as its grade maker, barely visible even under 10x magnification from the face-up view, while the other has a black crystal dead center.
When reviewing a grading report, check the first item in the Key to Symbols and locate it on the clarity plot. If it’s positioned under the table and described as a dark crystal or a large cloud, that inclusion is more likely to affect the diamond’s appearance. If it’s a feather or needle off to the side, you may have found a stone that “faces up” cleaner than its grade suggests.
For feather inclusions listed as the grade maker, look at whether the plot shows the feather reaching the surface or the girdle edge. Labs grade feathers conservatively because of durability concerns, which means diamonds with feathers as their prominent characteristic sometimes look better than diamonds with dark inclusions at the same grade. The tradeoff is a small theoretical risk to the stone’s integrity, one that matters more for a ring worn daily than for earrings or a pendant.