Diamond Certification
Why Certification Matters
A diamond certificate — also called a grading report — is an independent assessment of a diamond's quality. Issued by a gemological laboratory, it documents the stone's characteristics using standardised criteria so that buyers can compare diamonds objectively.
Without certification, you are relying on a seller's word. A grading report from a reputable laboratory gives you verified, unbiased information about exactly what you are buying. It is the single most important document in any diamond purchase.
Major Grading Laboratories
The two most widely recognised diamond grading laboratories are GIA (Gemological Institute of America) and IGI (International Gemological Institute). Both assess diamonds using the 4Cs framework — cut, colour, clarity, and carat weight.
GIA — Gemological Institute of America
GIA created the 4Cs grading system and is considered the gold standard in diamond certification. Their reports are the most widely accepted globally and are known for consistent, conservative grading. GIA grades both mined and lab-grown diamonds, with lab-grown reports clearly noting the stone's origin.
IGI — International Gemological Institute
IGI is the largest independent gemological laboratory and has become particularly prominent in lab-grown diamond certification. Their reports are widely accepted by jewellers and retailers worldwide. IGI grading is generally consistent with GIA, though minor differences in colour and clarity assessment can occur between any two laboratories.
What Is on a Grading Report
A standard diamond grading report includes the following information:
- Report number — a unique identifier that can be verified on the laboratory's website
- Shape and cutting style — round brilliant, oval, emerald, cushion, and so on
- Measurements — dimensions in millimetres and depth/table percentages
- Carat weight — measured to the hundredth of a carat
- Colour grade — D (colourless) through Z (light colour)
- Clarity grade — FL (flawless) through I3 (included)
- Cut grade — Excellent to Poor (for round brilliant only at GIA)
- Polish and symmetry — separate grades for surface finish quality and facet alignment
- Fluorescence — the intensity of ultraviolet light reaction, from None to Very Strong
- Origin — whether the diamond is natural or laboratory-grown
Certification for Lab-Grown Diamonds
Lab-grown diamonds are certified using exactly the same criteria as mined diamonds. The grading report will note that the stone is laboratory-grown, but the assessment of cut, colour, clarity, and carat weight follows the same standards and methodology.
This means a certified lab-grown diamond gives you the same confidence in quality as a certified mined diamond. You can verify the grade independently, compare stones objectively, and know that the assessment was performed by trained gemologists under controlled conditions.
Learn more about lab-grown diamonds in our guide to whether lab-grown diamonds are real.
What to Look For
Always buy a diamond that comes with a grading report from GIA or IGI. Verify the report number on the laboratory's website to ensure it matches the stone being sold. Be cautious of certificates from lesser-known laboratories — their grading may be less consistent, making it difficult to compare diamonds accurately.
Pay particular attention to the cut grade, as this has the greatest impact on how a diamond looks. A diamond with excellent cut but slightly lower colour or clarity will typically look better than a higher-graded stone with a mediocre cut. Our 4Cs guide explains how to balance these factors for the best value.
Shop Certified Diamonds
Every LILY DIA diamond comes with an independent grading report. We work exclusively with certified stones so you can see exactly what you are getting — no guesswork, no ambiguity.