IGI Certificate: How to Read It and What It Really Reveals

The International Gemological Institute was founded in Antwerp in 1975. Today, it operates laboratories in the world’s leading global trade centers (New York, Hong Kong, Tokyo, Milan, Dubai) and is considered one of the most authoritative gemological institutes worldwide.

Its mandate is strictly technical: IGI analyzes and grades diamonds according to internationally recognized standards, without buying or selling stones. This independence is the foundation of its credibility. When a diamond carries IGI certification, its characteristics have been determined by a laboratory with no commercial interest in the stone itself.

The result is a document that transforms a unique gemstone into an asset that can be evaluated, made transparent, and tracked over time, essential not only at the moment of purchase, but especially when considering a future sale.

Certificate Formats

The IGI report is issued in two formats. The first is the full paper document, which includes all the stone’s technical specifications, inclusion diagrams, proportions, and any laboratory notes. It is the preferred format for those who require comprehensive documentation.

The second is the sealed blister: a tamper-evident transparent case that holds the diamond along with its key details. Once opened, it cannot be resealed without leaving visible signs, a level of protection designed to ensure the stone’s integrity throughout the entire commercial chain.

How to Read an IGI Certificate

The report follows a standardized structure. Each section has a specific purpose, and when read together, they provide a complete profile of the stone

• Identification Details

At the top of the document appear the IGI insignia, the issuing laboratory, the date of issuance, and the Report Number— the certificate’s unique identifier. This element serves as the central reference point: it enables verification of the document through IGI’s official database, precise identification of the stone within the international registry, and alignment with any laser inscription engraved on the diamond’s girdle.

The certificate further specifies whether the stone is a natural diamond (Natural Diamond) or a laboratory-grown diamond (Laboratory Grown Diamond)—a distinction that materially influences its positioning and value on the market.

• Carat Weight

The weight is expressed to two decimal places. Even minimal differences can have a direct impact on value: diamonds weighing one carat or more fall into the premium segment of the market, and crossing this threshold carries a tangible effect on pricing. The 0.50 to 0.99 carat range is highly sought after and often offers a compelling balance between quality and accessibility.

• Color

IGI grades color on an alphabetical scale from D to Z, where D represents a perfectly colorless diamond and Z indicates a stone with clearly visible yellow tones. The main ranges are:

D – E – F: colorless diamonds, among the rarest and most sought-after on the market
G – H – I: near colorless, often offering the most refined balance between quality and value
J – K – L: faint yellow tones, still appreciated in certain settings
M – Z: increasingly noticeable color, with a growing impact on valuation

When the color has not been treated, the certificate includes the notation “No indication of color enhancement”, a mark of natural origin that the professional market considers essential.

• Clarity

Clarity refers to the presence of internal inclusions or surface imperfections, assessed under 10x magnification. The IGI scale begins with FL (no visible inclusions) and progresses through VVS, VS, and SI, down to I1–I3, where inclusions become visible to the naked eye.

The certificate includes a diagram indicating the precise location of each inclusion: red symbols identify internal characteristics, while green marks denote surface imperfections. This map serves as the stone’s unique fingerprint—one of the most reliable tools for confirming its correspondence with the certificate.

• Cut, Symmetry and Polish

For round brilliant diamonds, IGI evaluates three distinct parameters: Cut, Polish, and Symmetry. Each is graded on a scale from Poor to Excellent. When all three achieve an Excellent grade, the diamond is classified as Triple Excellent —an especially sought-after standard for high-quality stones.

The report also details the stone’s technical proportions: table percentage, total depth, and the crown and pavilion angles. These are the metrics that allow specialists to assess the diamond’s true optical performance — how it captures light, how it reflects it, and how it behaves under different lighting conditions.

• Measurements, Fluorescence and Notes

Measurements are expressed in millimeters. Fluorescence describes the stone’s reaction to ultraviolet light and is graded from None to Very Strong, a parameter that can influence both visual appearance and, in certain contexts, market perception.

The Comments section may include additional relevant information: the presence of a laser inscription on the girdle, notes on specific treatments, or particular observations made by the laboratory.

Laser Inscription and Sealed Blister: Traceability Over Time

IGI certification extends beyond the paper report. Many diamonds feature a laser inscription on the girdle bearing the certificate number — visible only under magnification, yet sufficient to ensure the match between stone and report even after years and multiple transfers of ownership. This marking does not affect the diamond’s brilliance in any way.

The sealed blister provides an additional, tangible layer of protection: once opened, it cannot be resealed without leaving visible evidence. A system designed to protect both seller and buyer, ensuring that the stone has not been substituted or altered after certification.

How to Obtain an IGI Certificate

If a diamond has not yet been certified, an IGI report can be obtained through the official laboratories of the International Gemological Institute or via trusted industry professionals who collaborate with the institute. The stone is submitted for analysis and is typically returned with its certificate within a few days, usually up to one week.

The cost depends on carat weight and the type of report. As a general guideline, fees start at approximately €70 to €100 for smaller stones and can reach several hundred euros for more significant diamonds. For high-value stones, particularly those above one carat or with superior characteristics, certification by IGI, GIA or HRD has become a standard within the professional market. 

The Certificate Is the Starting Point, Not the Final Word

Understanding how to read an IGI certificate is a valuable capability. However, a gemological report describes a stone, it does not define its market value. Carat weight, color and clarity are objective parameters. Their translation into a concrete price depends on variables that evolve over time, including current demand, pricing dynamics and actual selling opportunities.

At Auctentic, we work daily with both certified and uncertified diamonds. This allows us to provide evaluations based not only on documentation, but on real market conditions, with the transparency and expertise of those who operate within the industry.

If you are considering enhancing the value of a diamond or preparing it for sale, our team is available for a professional assessment with no obligation. Whether your stone is accompanied by an IGI, GIA or HRD certificate, or no documentation at all, we can evaluate it with the same level of precision and help you clearly understand its true value and the most appropriate next steps.

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