Diamond Certification: What Buyers Should Know

A diamond certificate, also called a grading report, describes the characteristics of a diamond as assessed by a gemological laboratory. It is one of the most useful tools when buying a diamond, but only if you understand what it shows and what it does not.

What is a diamond certificate?

A diamond certificate is a document issued by an independent laboratory after examining a stone. It records measurable details such as the shape, dimensions, carat weight, colour grade, clarity grade and cut quality where applicable. It also identifies other characteristics, such as polish, symmetry and fluorescence, and often includes a diagram showing the position of inclusions.

Why certification matters

Diamonds look very similar to the eye but can differ significantly in quality and price. A report from a respected laboratory gives you an objective description so that you can compare stones. It also helps confirm that the diamond you receive is the one described by the seller.

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Well-known grading laboratories

Several laboratories issue diamond reports. Names you may see include the Gemological Institute of America (GIA), the International Gemological Institute (IGI) and the American Gem Society (AGS). They are widely recognised, but they do not all apply identical standards. Grades from different laboratories on the same stone can differ. When comparing diamonds, compare reports from the same laboratory where possible and find out how strictly it grades.

What does a certificate include?

• Report number: a unique identifier, often verifiable on the laboratory's website.
• Shape and cutting style: for example round brilliant or oval.
• Measurements: dimensions in millimetres.
• Carat weight: the weight of the stone.
• Colour grade: the degree of colourlessness for white diamonds.
• Clarity grade: based on inclusions and blemishes.
• Cut grade: provided on many reports for round brilliant diamonds, and in different forms for other shapes.
• Polish and symmetry: the quality of the finish.
• Fluorescence: reaction under ultraviolet light.
• Clarity plot: a map of the main inclusions.

Our guide to reading a diamond grading report goes through these in detail.

Does it say if the diamond is natural or lab-grown?

Reports from reputable laboratories typically state whether a diamond is natural or laboratory-grown. This is important when you are comparing prices, because the two types are priced differently. Check this detail against what the seller has told you.

A certificate is not a valuation

A grading report describes a diamond's characteristics. It does not tell you what the diamond is worth, and it is not an insurance valuation. If you need a valuation for insurance, ask an independent qualified appraiser.

Check that the report matches the diamond

Many diamonds have a tiny laser inscription on the edge, called the girdle, which can include the report number. A jeweller can show you this under magnification. Compare the report number, measurements and weight with the stone and the product listing. If something does not match, ask the seller to explain before you buy.

Verify the report

Many laboratories let you check a report number online. This confirms that the report exists and that the details match. If you cannot verify a report, or the seller discourages you from checking, treat it with caution.

Is a certificate always necessary?

For a significant diamond, such as an engagement ring centre stone, a report is strongly recommended. For small diamonds in fashion jewellery, such as the many tiny stones in a pavé band, individual certificates are not usually provided. In these cases, the seller should still describe the total carat weight and the general colour and clarity range accurately.

Questions to ask the seller

• Which laboratory graded the diamond?
• Can I see the full report and verify its number?
• Is the diamond natural or lab-grown?
• Is the diamond inscribed with the report number?
• What is your return policy if the stone does not match the report?

Limits of a certificate

A report cannot tell you how a diamond looks in person. Two diamonds with the same grades can appear different because of their cut details and inclusion positions. Use the certificate together with photographs, video and, where possible, a physical inspection.

Buy with confidence

A report combined with a transparent seller and a good return policy gives you a solid basis for decision. To see diamond jewellery with clear specifications, explore our certified diamond collection.