Gemstone Certificates & Grading Reports

How to be certain that a gemstones is genuine? For the layman and even for an expert without a full set of laboratory equipment, it is very difficult to check gemstones for authenticity and to classify them correctly. It is even more difficult to determine if a gem was treated or enhanced and almost impossible to determine the origin of a gemstone without a lab.

Therefore, certificates and grading reports from independent gemological laboratories are important. Certificates from recognized gemological labs specify the unique characteristics and qualities of a gem and verify grading and authenticity of the precious stone.
A certification is of the highest importance when buying gemstones as it not only reduces risks but also increases the value of the gem and is crucial for later resale.
Also insurance companies insist on the presentation of the certificate in addition to a commercial invoice in order to be able to insure a gemstone.

Gemstone certification

A gemstone certificate contains or proves the following:

  • Gemstone name, e.g. “ruby” or “tanzanite”.
  • Type of mineral , e.g. for ruby: corundum
  • A photo of gemstone
  • Weight in carat (ct.)
  • Dimensions in mm
  • Information whether it is a natural gemstone or a synthesis
  • Color, mostly including saturation
  • Information, if the gemstone is natural color (or if e.g. heat treated)
  • Information if the gemstone is otherwise treated (e.g. fracture-filled, impregnated, irradiated, or diffused)
  • Optional: a confirmation of geographic origin of the gemstone
  • For diamonds, additional information on clarity, color grade, fluorescence, and quality of cut, symmetry, and polish.

Be careful with “certificates” issued by gemstone dealers or jewelers! These are usually not generally recognized documents. In the case of resale, such “certificates” or “reports” are almost worthless.

For colored gemstones, certificates from Swiss labs, e.g. from the Swiss Foundation for Gemstone Research (SSEF), Swiss Research Gemlab (GRS) or Dunaigre have the best international reputation. For diamonds, diamond grading reports and dossiers from the GIA (Gemological Institute of America) have the best international reputation.

When buying gemstones, always look for certificates from independent gemological laboratories!

Which certificates are internationally recognized?

For colored gemstones, there are numerous institutes and laboratories that issue recognized certificates and grading report:

  • Swiss Gemological Institute (SSEF)
  • GemResearch Swisslab (GRS)
  • Gübelin
  • Dunaigre
  • GIA
  • Lotus
  • International Gemological Institute (IGI)
  • Gemmological Institute of India (GII)
  • Ceylon Gem Lab (CGL)
  • und andere

For diamonds, certificates from the Gemological Institute of America (GIA) and the “Hoge Raad voor Diamant “(High Council for diamonds) of the Antwerp Diamond Exchange (HRD) are considered the two most important certifications.
Also certificates of the ” International Gemological Institute” (IGI) should also be mentioned here.

The certificates for diamonds and for colored gemstones are mostly similar in structure.

Colored gemstones certifications

Colored stone identification reports and certificates for colored gemstones differ in appearance depending on the issuing laboratory or institute.

In any case, a certificate must contain:

  • Name of the issuing institute
  • Certificate number
  • A photo of the gemstone
  • The dimensions of the stone, including weight, to the nearest hundredth of a millimeter or hundredth of a carat (at some institutes to the nearest thousandth of a carat.)
  • The mineral e.g. corundum or beryl
  • The name of the gemstone e.g. “ruby”
  • A statement whether it is a natural gemstone or a synthesis
  • The color of the stone (for a ruby, “red” is derived from the gemstone itself, for a sapphire, the color needs to be specified)
  • A statement about whether the stone is of natural color, untreated or was heat-treated
  • A statement as to whether the stone is otherwise treated or enhanced (e.g., fracture-filled, impregnated, irradiated, or diffused)
  • Optional: the geological origin of the gemstone.

The origin reports to confirm the geographic origin of a stone must be ordered separately by the owner.
For some stones it makes no sense: almost all intense yellow sapphires come from Sri Lanka, so the determination of the origin makes no difference to the value.

Quite different with ruby: since rubies with the origin “Burma” archive higher prices, the determination of origin is essential here.

In certificates the following special remarks about the color can be found for rubies:

  • “Pigeon blood”: the most expensive of all colors, it is given only for natural colored rubies and raises the price substantially.
  • “Intense/vivid red”: this is a gradation to “pigeon blood” and also increases the price.

For blue sapphires, there are two internationally demanded color grades:

  • “Royal blue”: this designation for a dark blue of high saturation with high brilliance is the most sought-after and most valuable
  • “Cornflower blue”: this color grade is also a highly precious variety. It describes a very purely blue without the typical undertones of green or purple seen in blue sapphires.

The cost of a certificate ranges from around 30 euros at a local institute, as in India or Sri Lanka, to several 1,000 euros for correspondingly high-quality and rare gemstones. The purchase price of the gemstone thus also has a certain influence on which certificate one receives when buying a stone: if the stone costs 500 Euros, for example, the buyer cannot expect an SSEF or GRS certificate.

The determination of origin can be ordered extra by the owner of the stone. It is usually expensive and often adds up to 50% of the total cost of the certificate.

Diamond grading reports: GIA or HRD

The two main certification labs for diamond grading are the Gemological Institute of America (GIA) and the HRD. Certificates from other labs may lead to significant price reductions when reselling.

In the past, diamonds that have been certified were sealed in plastic boxes. On the plastic box was the certification number and so the diamond was linked to the certificate. Today this is no longer state of the art. Today, the number of the certificate is laser inscribed on the girdle of the diamond (thin outer edge) in letters no larger than a few micrometers and so invisible to the naked eye. In this way, the connection between the diamond and the certificate is established.

If you want to check whether the certificate is genuine, you can enter the number of the certificate on the website of the certifying institute and you will get a scan of the respective certificate. (Of course, ownership data is not public.)

A diamond certificate can be considered as part of the proof of ownership. In any case, certificates should be kept separate from gemstones.

A note about the types of GIA diamond certificates: If the diamond is larger than 1 carat, the “GIA Diamond Grading Report” (21.6 x 9.3 cm) is enclosed. If a diamond weighs less than 1 carat, the “GIA Diamond Dossier” measures 12.8 x 9.3 cm.

Contents are indicated in the diamond certificate:

  • Certificate number
  • Cut (brilliant, emerald, oval or princess cut, etc.)
  • Dimensions of the diamond to the nearest hundredth of a millimeter
  • Weight in carat to the nearest hundredth of a carat
  • Color from D to Z
  • Clarity grade from FL to P3
  • Cut grade from “excellent” to “poor
  • Polish from “excellent” to “poor
  • Symmetry from “excellent” to “poor
  • Fluorescence from “none” to “strong”
  • Other characteristics of the diamond
  • A profile of the cut
  • For diamonds heavier than 1 carat, a schematic representation of the inclusions, if applicable, is also provided.

A photo of a white diamond is omitted from most certificates as it would not have much informational value, the above parameters are more important.

Usually all white diamonds of good quality with a weight from 0.33 ct. are certified. If the weight is less than that and the buyer wants a certificate, he will be charged separately for it.

For colored “fancy diamonds”, the color is not mentioned in the scale D-Z, but the corresponding color designations (e.g. “fancy intense yellow”). All other information remains the same. Certificates of the GIA for colored diamonds (GIA Colored Diamond Identification and Origin Report) are always 21.6 x 9.3 cm.

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Dr. Thomas Schröck
The Author:

Dr. Thomas Schröck

The founder and managing partner of THE NATURAL GEM has been active in international gemstone trading for 30 years. As a doctor of economics and a certified gemmologist in Switzerland, Germany and the USA, among other countries, he is one of Europe’s leading experts on naturally-coloured, untreated gemstones and investments in them.


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