How to Compare Two IGI Diamond Certificates Side by Side Before Buying

Two IGI grading reports for lab-grown diamonds with identical stated grades can price out hundreds of dollars apart. Knowing which fields to compare, and in what order, is what separates a buyer who gets genuine value from one who simply pays less for a worse stone. The four core grades (cut, color, clarity, carat) account for roughly 90 percent of a diamond’s value, but the secondary fields on the certificate are often where the real differences hide.

IGI has become the standard grading lab for lab-grown diamonds, and every report it issues follows a consistent layout: the report number sits at the top, the grading results in the center, and the proportions diagram to the right. Once you know where each field lives, any two IGI reports can be read the same way, side by side, in about ten minutes.

What fields on an IGI certificate actually drive value?

Cut, color, clarity, and carat weight are the four fields that matter most. Pull both certificates and read each grade in that order before you look at anything else.

Carat weight is recorded to two decimal places. A stone listed as “1.00 ct” and one at “1.09 ct” carry the same color and clarity grades on paper, but the size difference is visible and the price difference is real. Always check the exact number, not the rounded marketing label.

Color runs D (colorless) through Z. Lab-grown diamonds tend to grade D through F more often than mined stones do, so the spread between two IGI-certified lab diamonds at, say, E versus G color is measurable in both appearance and price. Colorless (D, E, F) stones cost more; near-colorless (G, H, I, J) are often the smarter spend when set in white gold or platinum, since the metal masks any warmth.

Clarity runs from Flawless down through SI2. VS2 and above is considered eye-clean by most gemologists, meaning inclusions are not visible to the naked eye. Comparing two stones where one grades VS1 and the other VVS2 at the same price point probably means the VS1 stone has a better cut or larger carat weight. Check the clarity plot on each certificate: two VS1 stones can have very different inclusion types and positions.

Cut grade applies specifically to round brilliant diamonds and runs from Excellent to Poor. A stone with average color and clarity but an Excellent cut will outperform one with better color and clarity but a weaker cut in terms of visible sparkle. When comparing two rounds, this field should not be skipped.

How do the secondary fields change the comparison?

Once the four core grades match between two certificates, the secondary fields are where one stone pulls ahead.

Polish and symmetry are each graded Excellent to Poor. For round brilliants, IGI evaluates both as distinct parameters alongside cut, and all three need to achieve Excellent for a stone to earn a Triple Excellent designation. The overall cut grade is effectively capped by whichever of the three is lowest, so a stone with Very Good symmetry cannot carry an Excellent cut grade regardless of its proportions. When two diamonds match on the 4Cs, the one with Excellent polish and symmetry versus Very Good will typically hold its appearance better under close inspection.

Fluorescence describes how the stone reacts under ultraviolet light, graded from None to Very Strong. For D through F color lab-grown diamonds, None fluorescence is generally preferred: strong fluorescence can introduce a slight haziness in direct sunlight. If one of the two certificates shows Medium or Strong fluorescence on a colorless stone, that alone can justify a price difference and is worth factoring into your decision.

Growth method is a field specific to lab-grown diamond certificates. IGI reports note whether the stone was grown via CVD (Chemical Vapor Deposition) or HPHT (High Pressure High Temperature). Both methods produce diamonds graded on identical 4C scales, so this field rarely changes the value calculation, but it is useful context if you have a preference.

How do you verify the certificates are authentic before comparing them?

Before spending any time comparing grades, confirm both reports are real. IGI lab-grown diamond report numbers use the format LG followed by a string of digits. Go to IGI.org, open the Verify Your Report tool, enter each number, and the official certificate loads with full grading details. The process takes under three minutes per stone and costs nothing.

After verifying online, check that the laser inscription on the diamond’s girdle matches the report number exactly. A jeweler can show you this under a loupe or microscope. Any mismatch between the physical stone and the certificate is a reason to stop and ask questions before proceeding.

This step matters more than it sounds. Counterfeit or altered certificates exist in the market, and skipping verification is the single most avoidable mistake a buyer can make.

How do you turn two verified certificates into a side-by-side price comparison?

Once both reports are verified and the grades are aligned, the comparison becomes straightforward. Build a simple table with seven rows: carat, color, clarity, cut, polish, symmetry, and fluorescence. Fill in the grade from each certificate in separate columns. Any cell where the grades differ is a line item that explains a price gap.

If both stones match on every field and one is cheaper, the difference is retail markup, not quality. If the cheaper stone carries a lower cut grade or Very Good symmetry where the other shows Excellent, the price gap is probably justified. The certificate tells you which scenario you are in.

One thing to watch: a stone that grades higher on color but lower on cut is not automatically the better buy. Cut governs how the diamond handles light, and a poorly cut stone with G color will look duller than a well-cut stone with H color. Prioritize cut and carat, then let color and clarity fill in around your budget.

The Certificate Is the Diamond on Paper

When two IGI reports cover the same shape and similar size, the comparison is almost mechanical: verify both, align the seven fields, and identify where they diverge. The fields that diverge explain the price difference. The fields that match confirm you are comparing equivalent stones.

For buyers shopping IGI-certified lab-grown diamonds, having both certificates open at once is the fastest way to see whether a price premium is backed by a real quality difference or is just markup. Ouros Jewels publishes IGI grading details directly on each product page, which makes the field-by-field check straightforward without requesting paperwork separately.

The one field that tends to decide a close comparison is cut. Everything else being equal, the stone with the stronger cut grade will look better in a ring, in a photograph, and in person.

Frequently Asked Questions

Can I compare an IGI certificate with a GIA certificate for a lab-grown diamond?

You can, but the comparison requires an adjustment. GIA grades more conservatively than IGI, so a GIA G color is roughly equivalent to an IGI F color. As of 2026, GIA no longer issues standard letter grades for lab-grown diamond color and clarity, using descriptive ranges instead, which makes a direct side-by-side comparison with an IGI report difficult.

What does the clarity plot on an IGI certificate tell me when comparing two stones?

The clarity plot maps the type, size, and position of each inclusion. Two diamonds graded VS1 can look very different under magnification depending on whether inclusions are near the center of the table or tucked near the girdle. A centrally placed inclusion is more visible than one at the edge, so always read the plot alongside the clarity grade.

Is a higher carat weight always better when comparing two IGI-certified lab diamonds at the same price?

Not automatically. A heavier stone with a weaker cut grade can look smaller and duller than a lighter stone cut to Excellent proportions, because poor cut geometry causes light to leak out the bottom rather than reflect back to the eye. Carat weight affects size on paper; cut affects size in person.

What does the growth method field on an IGI lab-grown diamond certificate mean for my purchase?

IGI reports specify whether a lab diamond was grown via CVD or HPHT. Both methods produce chemically identical diamonds graded on the same 4C scale, so the growth method does not affect quality grades or typical pricing. It is informational context about how the stone was made, not a quality indicator.

How often should I re-verify an IGI report number if I am buying online over several days?

Verify the report number each time you return to a listing you are seriously considering, especially if the price changes or the listing is updated. The IGI public database is free and takes under three minutes. Verifying once at the start and once just before purchase is a reasonable minimum for any online transaction.