What the IGI Certificate Says About SI1 Clarity: How to Interpret the Inclusion Details

An SI1 lab grown diamond can be genuinely eye-clean or visibly flawed, and the IGI certificate tells you which one you have before you spend a dollar. The clarity grade alone does not settle the question. What settles it is the inclusion plot, the inclusion type descriptions, and the position of every symbol on that diagram.

SI1 sits at the point on the grading scale where judgment starts to matter. Grades above it, from VS2 upward, are almost always clean to the naked eye. SI2 frequently is not. SI1 is the grade where a well-positioned inclusion and a poorly positioned one can look completely different on a finger, even though both carry the same three letters on paper. Reading the certificate correctly is the difference between a beautiful stone and one you will always notice.

What does the IGI clarity grade actually measure?

IGI grades clarity under 10x magnification, assessing inclusions on the same eleven-point scale used for natural diamonds: FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, and I3. SI1 sits at the “Slightly Included” tier, meaning inclusions are noticeable immediately at 10x magnification. The critical thing to hold onto is that you will never wear your diamond under a loupe. The grade is assigned under magnification; you live with the stone without it.

That gap between grading conditions and wearing conditions is exactly why an SI1 can be a smart buy or a disappointment depending on which stone you pick. Around 80 to 85 percent of SI1 lab grown diamonds end up eye-clean in practice, which means roughly one in six does not. The certificate is the tool that helps you land in the right group.

How do you read the inclusion plot on an IGI report?

The clarity plot is a top-down and bottom-up diagram of the stone, with colored symbols showing where each clarity characteristic sits. Red symbols mark internal inclusions; green symbols mark surface blemishes. Think of it as a map, not a report card. The grade is already printed above it. What the plot adds is geography.

Position is the only thing to focus on. An inclusion at the edge of the stone, near the girdle, will often sit under a prong in a finished ring and disappear entirely. An inclusion directly under the table facet, the large flat panel on top, sits in your line of sight every time you look at the ring. Two stones can share an SI1 grade with identical symbol counts and look nothing alike, because one has its inclusions tucked at the perimeter and the other has them centered.

When the plot is present on your report, run through three checks in order. First, locate every red symbol and note whether it falls inside the table circle or outside it toward the girdle. Second, check whether any symbols cluster together rather than spread out. A cluster concentrates visual weight in one spot and is harder for a brilliant cut to scatter with light. Third, look at whether any symbols appear in the pavilion diagram in a position that would reflect back through multiple facets. An inclusion reflected in the pavilion creates a hall-of-mirrors effect that multiplies its apparent size.

What if the inclusion plot is missing from the report?

Since 2026, IGI has moved to a modular reporting structure where the clarity plot is an optional add-on that the seller elects, rather than a default element on every lab-grown diamond report. The clarity grade itself is still assessed and printed either way. If you receive a report without a plot, ask the seller for a high-resolution video of the stone face-up. A 360-degree video at actual scale will tell you more than a diagram anyway, because you see light performance rather than a static symbol.

Which inclusion types on the certificate raise the most concern?

The certificate lists each inclusion by name in the key to symbols. Not all types behave the same way visually. A pinpoint is a single tiny dot, usually transparent, and rarely a problem at SI1. A feather is a small internal fracture; a white or transparent feather near the girdle is manageable, but a large feather under the table can catch light in a way that draws the eye. A crystal is a mineral deposit trapped inside the stone; dark or black crystals are the most visible inclusion type at any size and the ones most likely to make an SI1 fail the eye-clean test.

Lab grown diamonds carry their own characteristic inclusion types depending on growth method. CVD stones may show cloud-like formations or planar features from layered growth. HPHT stones occasionally contain metallic flux inclusions, which appear as dark needles or iron-colored specks. Neither type disqualifies a stone, but a dark metallic needle centered under the table is a different situation from a faint cloud near the girdle.

Does carat size and shape change how SI1 inclusions read?

Yes, and this is the factor buyers most often overlook. The same inclusion that is invisible in a 1 carat round brilliant can become visible in a 2 carat stone of the same shape, because the larger table gives the eye more surface area to scan. Brilliant cuts, including round, cushion, and radiant shapes, scatter light aggressively and tend to hide inclusions well. Step cuts, specifically emerald and asscher, have large open tables and very little sparkle to mask anything. An SI1 emerald cut is a genuine risk; an SI1 round brilliant under 1.5 carats with edge-positioned inclusions is often a strong buy.

The shape interaction is worth keeping in mind when browsing IGI certified lab grown diamonds. A radiant cut, for instance, sits in a favorable position for SI1 clarity because its brilliant faceting breaks up inclusions the way a round does, while its rectangular outline gives the impression of a larger stone at the same carat weight.

Inclusion Position Decides the Eye-Clean Question

The IGI certificate gives you the data. Whether an SI1 lab grown diamond is worth buying comes down to one thing: where the inclusions sit on the plot, not how many there are or what the grade says in isolation. A single dark crystal under the table fails. A cluster of pinpoints near the girdle, hidden by a prong, passes. Read the plot before the grade, check the inclusion type names in the key, and watch a face-up video at actual scale.

For buyers who want to skip the evaluation entirely, stepping up to VS2 removes most of the uncertainty, though it costs more. For buyers willing to spend ten minutes with a certificate and a video, a well-chosen SI1 lab grown diamond, like those in the IGI certified round lab grown diamond stud earrings at Ouros Jewels, can look identical to a VS stone on the finger at a meaningfully lower price.

Frequently Asked Questions

Can I trust an SI1 lab grown diamond to be eye-clean without seeing the inclusion plot?

No. The grade alone is not enough. Roughly 15 to 20 percent of SI1 lab grown diamonds have inclusions visible to the naked eye, usually because a dark crystal or large feather sits under the table facet. Always request the inclusion plot or a face-up 360-degree video before purchasing any SI1 stone.

What is the worst inclusion type to see on an IGI certificate for an SI1 diamond?

A dark or black crystal sitting under or near the center of the table is the most problematic inclusion at SI1 clarity. It is opaque, it does not scatter light, and it tends to remain visible even in brilliant cuts. Transparent feathers and pinpoints near the girdle are far less likely to affect the stone’s appearance.

Does the IGI clarity plot work the same way for fancy shapes as it does for round brilliants?

The plot uses the same symbol system regardless of shape, but the risk profile changes. Step cuts like emerald and asscher have large, open tables that expose inclusions, making SI1 a higher-risk grade for those shapes. Brilliant cuts including round, cushion, and radiant hide inclusions more effectively, so the same plot position is less concerning in a brilliant shape than in a step cut.

If an IGI report has no inclusion plot, is the stone lower quality?

Not necessarily. Since 2026, IGI has made the clarity plot an optional paid element on lab-grown diamond reports, so its absence reflects a seller’s reporting choice rather than a quality issue with the stone. The clarity grade is still assessed by the same gemologists using the same 10x standard. Ask the seller for a high-resolution video to compensate for the missing diagram.

At what carat size does SI1 clarity become harder to keep eye-clean?

The risk increases noticeably above 1.5 carats in brilliant cuts, because the larger table gives the eye more area to scan. Above 2 carats, the same inclusion that disappears in a smaller stone can become visible. For stones over 2 carats, most buyers are better served by VS2 clarity to stay comfortably eye-clean without needing to audit the plot as carefully.