How to Use the IGI Clarity Plot to Evaluate an SI1 Lab Grown Diamond Before Buying

An SI1 lab grown diamond can look completely clean to the naked eye or show a visible flaw depending on where its inclusions sit, with position mattering far more than total count. Reading the IGI clarity plot before you buy is what separates a smart purchase from an expensive disappointment.

The grade itself tells you only that inclusions were “noticeable under 10x magnification.” IGI graders do not make eye-clean judgments, because too many variables affect what a person sees at arm’s length under normal lighting. That responsibility falls to you, and the clarity plot is the tool that makes it possible.

What exactly is the IGI clarity plot, and what does it show?

The clarity plot is a diagram of the diamond viewed from above (crown) and below (pavilion), annotated with colored symbols that mark every inclusion and blemish identified during grading. Red symbols indicate internal characteristics such as crystals, feathers, and clouds; green symbols mark surface blemishes. The four inclusion types you will encounter most often are pinpoints (single tiny dots), feathers (small internal fractures), clouds (clusters of pinpoints), and crystals (a separate mineral trapped inside the stone).

One practical detail worth knowing: some IGI reports omit a full symbol legend and state only that red means internal and green means external. If you want to identify a specific inclusion type by name, cross-reference the Comments field on the same report, which sometimes names the significant characteristics directly.

The plot also functions as a fingerprint. No two diamonds carry identical inclusion patterns in identical locations, so the diagram lets you confirm that the stone you receive is the same one IGI graded.

Why does inclusion position matter more than inclusion count?

Position is what the plot is really for. An inclusion sitting at the edge of the stone will be hidden by a prong once the diamond is set. An inclusion sitting directly under the table facet, the large flat surface on top, sits in your line of sight every time you look at the ring. Two stones both graded SI1, each carrying the same number of symbols on their plots, can be an easy yes and an easy no purely on where those symbols land.

Color matters too. A dark or black crystal reads as a visible spot more readily than a white feather of the same size, because the dark inclusion creates contrast against the bright facets around it. A transparent pinpoint near the girdle is almost never an issue, while a dark crystal centered under the table almost always is.

The Comments field deserves a second look here. A note reading “clarity grade is based on clouds not shown” signals that the stone may carry a diffuse haze that does not appear on the plot at all. That kind of haziness can dull a diamond’s face-up appearance even when the printed clarity grade looks respectable.

How does diamond shape change what the plot tells you?

Shape changes the risk profile of every SI1 stone you look at. Brilliant cuts, round, oval, cushion, radiant, pear, marquise, use a facet pattern that bounces light in dozens of directions simultaneously, which makes it harder for the eye to lock onto a single flaw. In our experience reviewing IGI reports, roughly 8 in 10 SI1 rounds with no table-area symbols photograph eye-clean. The plot can be fairly forgiving here: a single small symbol near the girdle on a round brilliant is rarely a problem.

Step cuts are a different situation. Emerald and Asscher cuts have long, open facets that act like windows into the stone. Inclusions that would disappear inside a round brilliant’s sparkle sit plainly visible in an emerald cut’s broad table. At SI1 in a step cut, the plot needs to be almost completely clear of symbols in the table area before the stone is worth considering. For those shapes, most buyers are better served by VS1 or VS2 clarity.

Carat weight adds another layer. The same inclusion that goes unnoticed in a 1.00 ct round brilliant can become visible in a 2.00 ct stone of the same shape, because the larger table gives the eye more surface to scan. Above about 1.5 carats, a round brilliant’s table diameter reaches roughly 7.3 mm, wide enough that the unaided eye can resolve detail it would miss on a 6.5 mm table, so treat every SI1 above that threshold as requiring individual review regardless of the plot’s apparent cleanliness.

What is the process for reading the plot before buying?

Start with the crown diagram, the top-down view, and identify any symbols sitting in the central octagonal area that represents the table facet. Those are the inclusions most likely to be visible face-up. If the table area is clear and symbols appear only near the outer edges or girdle, that is a positive sign. From there, check the symbol type: a small red dot (pinpoint) near the girdle is low risk, while a larger red shape in the center (crystal or cloud) warrants real caution. Check whether the Comments field names any characteristics not drawn on the plot, particularly any reference to clouds.

Then move to the pavilion diagram. Inclusions in the pavilion can reflect upward through the crown facets, so a symbol that appears to sit safely at the bottom of the stone may still be visible face-up depending on depth and position. A clean-looking plot is a good sign, but not a guarantee: a single dark crystal under the table can still be visible even when everything else looks fine on paper.

Pair the plot with a high-resolution face-up video if the seller provides one. The plot tells you where inclusions are; the video shows you whether they are actually visible at normal viewing distance. Both together give you a reliable answer that neither provides alone.

The Clarity Plot Is the Purchase Decision

For an SI1 lab grown diamond, the clarity grade is a starting point and the plot is the actual decision. A stone with one small pinpoint tucked near the girdle of a round brilliant will look identical to a VS2 on the hand, while a stone carrying a dark crystal centered under the table will show that flaw regardless of what the grade says. When shopping, confirm the seller provides the full IGI report PDF so you can apply this review before committing. Request the face-up video too, then compare it against the plot. Those two steps together are what makes an SI1 purchase predictable rather than a guess.

Ouros Jewels offers IGI certified lab grown diamonds with complete grading reports, so the clarity plot and Comments field are available to review before any purchase decision.

Frequently Asked Questions

Does a clean-looking IGI clarity plot guarantee an eye-clean SI1 diamond?

A plot may show only one or two symbols, but if those symbols represent a dark crystal centered under the table facet, the stone is likely visible to the naked eye. Conversely, a plot with several symbols scattered near the girdle often produces a completely eye-clean stone. Position and inclusion type decide the outcome, not the total number of symbols on the diagram.

Is an SI1 clarity grade reliable on an IGI certificate for lab grown diamonds?

IGI grades the majority of lab grown diamonds sold in the US market and uses the same D-to-Z color and FL-to-I3 clarity scales as GIA. The grade reflects what trained graders observed under 10x magnification. For SI1 stones in particular, the plot and Comments field on the IGI report give you the additional detail needed to judge face-up appearance independently.

Can the setting hide an SI1 inclusion that shows on the clarity plot?

Yes, in some cases. An inclusion plotted at or near the girdle of the stone can sit directly under a prong once the diamond is set, making it permanently invisible. This is worth discussing with your jeweler if you have identified a stone where the only concern is a single edge-positioned inclusion. It does not work for inclusions under the table, which no prong can cover.

At what carat size does an SI1 lab grown diamond become harder to buy safely?

Above roughly 1.5 carats, the table facet is large enough that inclusions become easier to detect without magnification, even in brilliant cuts. Above 2 carats, treat every SI1 as needing individual review regardless of shape. The clarity plot and a face-up video both become more important as carat weight increases, not less.

What does “clouds not shown” in the IGI Comments field mean for an SI1 stone?

It means the stone contains a diffuse cluster of tiny pinpoints spread across an area too large or too faint to draw accurately on the plot. Depending on size and density, this cloud can create a slight haziness that reduces the diamond’s face-up brightness. Always treat this comment as a reason to request a face-up video or an independent opinion before purchasing.