Understanding the Clarity Plot on an IGI Diamond Grading Report

The clarity plot on an IGI diamond grading report is an inclusion map printed as two schematic views of your stone. Red symbols mark internal inclusions trapped inside the diamond; green symbols mark external blemishes on its surface. Reading the plot tells you not just what characteristics exist, but exactly where they sit within the stone, which is the detail that actually determines whether those characteristics will affect how the diamond looks to the naked eye.

Most buyers glance at the clarity grade letter and move on. That is understandable, but the plot is where the useful information lives. Two diamonds can carry the same VS2 grade and look completely different in person, depending on whether their inclusions cluster under the table or hide near the girdle. The grade tells you the result; the plot shows you the geometry behind it.

What does the IGI clarity plot actually show?

The plot is a schematic diagram of your diamond’s outline, scaled to match its shape and facet arrangement, whether round, radiant, cushion, or any other cut. It features two views: the crown view from the top and the pavilion view from the bottom. Together they let you see how a characteristic visible from the face-up position corresponds to its position from below.

Superimposed on those outlines are small symbols, each representing a specific type of clarity characteristic. A solid circle typically indicates a crystal inclusion. A dotted circle suggests a cloud. A squiggly line represents a feather. A straight line marks a needle. The symbol’s position on the diagram tells you where that characteristic sits within the actual stone, and the color tells you whether it is internal or external.

IGI confirms this directly: their grading reports show plotted diagrams of clarity characteristics marked in red for internal features and green for external ones. Some IGI reports include a full key to symbols; others simply note that red means internal and green means external without labeling every symbol individually. If your report lacks a legend, the color rule alone is enough to orient you.

What do the red and green symbols mean in practice?

Red symbols are the ones that carry the most weight for most buyers. They represent inclusions enclosed within the diamond: crystals, feathers, clouds, needles, pinpoints, and similar internal characteristics. These form during the growth process, whether the stone grew underground over billions of years or inside a reactor over a few weeks.

Green symbols are surface blemishes, things like polishing marks, small scratches, or naturals along the girdle. Because they sit on the exterior, a skilled polisher can sometimes remove minor ones, and a prong or bezel setting can cover others entirely. For that reason, green marks on a plot tend to be less consequential than red ones, though a large surface blemish in a prominent position still matters.

There is a third scenario worth knowing: when red and green appear together on the same symbol, that indicates a characteristic that breaches both the interior and the surface, such as a cavity, a knot, or a laser drill hole. These are less common in lab-grown diamonds but worth flagging if you see them.

How does inclusion position change what the plot means?

This is where the plot earns its keep. The clarity grade is assessed at 10x magnification, but you will be wearing the diamond in normal light at normal viewing distances. An inclusion that dominates a 10x loupe view can be invisible to the naked eye if it sits near the girdle, where the setting’s prongs may cover it and where the facet geometry makes it harder to spot face-up.

Inclusions closer to the center of the table are generally more visible and have a greater impact on the perception of diamond clarity. Characteristics at the edges can be less noticeable and may even be obscured when the stone is mounted. So a plot that looks busy around the outer ring of the crown view is often less of a concern than a single red mark sitting dead center under the table.

A practical example: two SI1 diamonds can sit side by side with very different real-world appearances. If one has several small inclusions near the girdle and the other has a single feather clustered at the table center, the second stone is more likely to show something to the naked eye, even though both share the same grade. The plot is the tool that tells you which situation you are dealing with.

What does the clarity plot reveal about lab-grown diamond inclusions specifically?

Lab-grown diamonds carry inclusions just as natural diamonds do, though the character of those inclusions differs by growth method, and the plot will reflect that. CVD diamonds tend to show internal graining or faint cloud-like formations caused by the layer-by-layer carbon deposition process. HPHT diamonds occasionally contain metallic flux inclusions: tiny remnants of the iron, nickel, or cobalt catalysts used during growth. These typically appear as fine needles or pinpoints on the plot.

Neither type is inherently a problem at higher clarity grades. At VS1 or VVS, graining in a CVD stone is usually so faint it barely registers on the plot. The metallic needles in an HPHT stone at the same grade are typically microscopic and do not affect the diamond’s appearance to the naked eye. But knowing the growth method noted on your IGI report helps you interpret what you are seeing on the plot: a fine needle in an HPHT stone reads differently than a feather in a CVD stone, even if both appear as red marks.

The plot also functions as a fingerprint. Because no two diamonds share an identical pattern of characteristics in identical positions, the diagram is one of the ways a jeweler can confirm that the stone in your ring matches the certificate issued for it.

The Clarity Plot Is the Grade Behind the Grade

The clarity letter on an IGI report tells you where a stone lands on an 11-point scale from Flawless to I3. The plot tells you why. Position, type, and number of characteristics together explain the grade, and they also predict how the diamond will actually look on a finger rather than under a grading microscope.

When shopping for a lab-grown diamond, look at the plot alongside the grade. Red marks near the girdle in a VS2 stone are far less concerning than red marks at the table center in the same grade. Green marks near a prong position may disappear entirely once the stone is set. And a plot with a single, small, off-center red symbol is usually a better buy than a cleaner-looking grade with a centrally placed feather, even if the certificate numbers appear identical.

Ouros Jewels offers IGI-certified lab-grown diamonds with full grading reports, so you can review the clarity plot before purchasing rather than after.

Frequently Asked Questions

Does a busier-looking clarity plot mean the diamond will look worse to the naked eye?

Not necessarily. A plot crowded with small symbols near the girdle often belongs to an eye-clean diamond, because those characteristics are hidden by the facet geometry and the setting. What matters more than symbol count is symbol position: a single red mark at the table center can be more visible than a dozen marks scattered at the edges.

What is the difference between a feather and a crystal on the IGI clarity plot?

A feather is a small fracture inside the diamond, shown as a squiggly line on the plot. A crystal is a trapped mineral or carbon particle, shown as a solid circle. Feathers near the surface or along the girdle can affect durability in rare cases; crystals are generally stable. Both are marked in red as internal inclusions.

Can green symbols on an IGI clarity plot be removed or hidden?

Sometimes. Minor surface blemishes like small polishing marks can occasionally be removed by re-polishing, though that is a decision for a professional gemologist. Blemishes positioned near the girdle are frequently covered by prongs or a bezel setting once the stone is mounted, making them a non-issue in finished jewelry.

Why do some IGI reports not include a symbol legend on the clarity plot?

Some IGI report formats, particularly the card-style dossier, include only basic 4Cs data without a full plotting diagram or symbol key. The full paper report includes the complete plot with all characteristics mapped. When buying a lab-grown diamond, asking for the full IGI report rather than the card version gives you access to the complete inclusion map and any comments the grader noted.

How do I use the IGI clarity plot when comparing two diamonds at the same grade?

Look at where the red symbols fall on each plot. Symbols near the center of the crown view, particularly under the table facet, are more likely to be visible face-up. Symbols near the outer edges or concentrated on the pavilion view are generally less noticeable. Also check the “Key to Symbols” or comments section: a feather listed first in the characteristics list is typically the grade-setting inclusion, meaning it had the most influence on the clarity grade assigned.