Why Your Diamond Certificate Matters More Than You Think
When you buy a lab grown diamond engagement ring from a reputable jeweller, it comes with a certificate from an independent grading laboratory. Most buyers glance at it, note the carat weight and maybe the cut grade, and file it away. That's a missed opportunity.
Your IGI certificate is a detailed, independently verified record of exactly what you've bought. It tells you not just the size of your diamond, but its precise quality across four dimensions and understanding it gives you the confidence to know you've made the right choice, and the knowledge to compare stones accurately before you buy.
This guide walks through every section of an IGI lab grown diamond certificate, explains what each grade means in plain language, and tells you what to look for and what to watch out for.
What Is IGI and Why Does It Matter?
IGI stands for the International Gemological Institute. Founded in Antwerp in 1975, IGI is one of the world's largest and most respected independent diamond grading laboratories, with facilities in Antwerp, New York, Mumbai, Hong Kong, Tokyo, Dubai, and beyond.
For lab grown diamonds specifically, IGI is the industry standard. They were among the first major laboratories to develop dedicated grading reports for lab grown stones, and they now issue the majority of lab grown diamond certificates worldwide. When you see an IGI certificate with a lab grown diamond, you're looking at the most widely recognised and accepted form of quality verification in the industry.
Every IGI certificate is issued after the diamond has been physically examined by trained gemologists using calibrated instruments. The grades on the certificate are not estimates or approximations they are the result of a rigorous, standardised assessment process.
At Unii Jewels, every lab grown diamond in our collection comes with a full IGI certificate. The certificate number is also laser-inscribed on the diamond's girdle the thin edge around the widest part of the stone so you can verify the certificate matches your specific diamond at any time by entering the number at igireport.igi.org.
IGI vs GIA: Which Is Better for Lab Grown Diamonds?
The two most respected grading laboratories for lab grown diamonds are IGI and GIA (Gemological Institute of America). Here's how they compare:
- IGI The world's leading certifier of lab grown diamonds by volume. IGI developed dedicated lab grown grading reports earlier than GIA and has graded significantly more lab grown stones. IGI certificates are the most common for lab grown diamonds and are fully accepted by jewellers, insurers, and resellers worldwide.
- GIA The most prestigious name in diamond grading overall, particularly for natural diamonds. GIA expanded its lab grown grading programme in recent years and now issues full 4Cs reports for lab grown stones. GIA carries strong brand recognition, particularly in the US market.
For lab grown diamonds, both are excellent. IGI is the industry standard and the certificate you'll encounter most often. GIA is equally valid and carries additional prestige for buyers who are familiar with it from the natural diamond market. At Unii Jewels, we work primarily with IGI-certified stones.
How to Read Your IGI Certificate: Section by Section
1. Report Number
The unique identifier for your certificate. This number is also laser-inscribed on the girdle of your diamond. You can enter it at igireport.igi.org to verify the certificate is genuine and matches your stone. Always do this before completing a purchase it takes 30 seconds and confirms the certificate hasn't been misrepresented.
2. Shape and Cutting Style
This describes the physical shape of the diamond (Round, Oval, Pear, Emerald, Cushion, etc.) and the cutting style (Brilliant, Step Cut, Mixed). The shape affects the diamond's visual character; the cutting style affects how light moves through it.
3. Measurements
The physical dimensions of the diamond in millimetres. For round diamonds, this is expressed as a diameter range (e.g., 6.40–6.43mm) and depth (e.g., 3.96mm). For fancy shapes (oval, pear, emerald, etc.), it's expressed as length × width × depth.
Measurements matter because two diamonds of the same carat weight can have very different face-up sizes depending on how they're cut. A well-cut 1ct round brilliant typically measures around 6.4–6.5mm in diameter. A poorly proportioned stone of the same weight might measure 6.0mm noticeably smaller despite being the same carat weight.
4. Carat Weight
The weight of the diamond, expressed in carats (ct). One carat equals 0.2 grams. Carat weight is the most straightforward of the 4Cs it's a precise measurement, not a grade. However, carat weight alone doesn't determine how large a diamond looks. Cut quality and shape both significantly affect the face-up size of a stone relative to its weight.
A practical tip: consider going slightly under a round carat weight 0.9ct instead of 1ct, or 1.9ct instead of 2ct. The visual difference is negligible, but the price difference can be meaningful.
5. Colour Grade
Diamond colour is graded on a scale from D (completely colourless) to Z (visibly yellow or brown). The scale was developed by GIA and is used universally, including by IGI.
- D, E, F Colourless. The highest grades, commanding a significant premium. The difference between D and F is invisible to the naked eye.
- G, H Near colourless. The sweet spot for most buyers visually indistinguishable from D–F when set in a ring, at a significantly lower price.
- I, J Slightly tinted. Still appears white to the naked eye in most settings, particularly yellow or rose gold. A smart choice for budget-conscious buyers.
- K and below Noticeable warmth. Generally not recommended for white metal settings.
For white gold or platinum settings, G or H is the recommended sweet spot. For yellow or rose gold, I or J works beautifully the warm metal tone complements and masks any slight warmth in the stone.
6. Clarity Grade
Clarity refers to the presence of internal inclusions (tiny imperfections within the stone) or external blemishes. The IGI clarity scale runs from:
- FL (Flawless) No inclusions or blemishes visible under 10x magnification. Extremely rare.
- IF (Internally Flawless) No inclusions visible under 10x magnification; minor surface blemishes only.
- VVS1, VVS2 (Very Very Slightly Included) Inclusions extremely difficult to see under 10x magnification. Invisible to the naked eye.
- VS1, VS2 (Very Slightly Included) Inclusions difficult to see under 10x magnification. Invisible to the naked eye. Excellent value.
- SI1, SI2 (Slightly Included) Inclusions noticeable under 10x magnification. Usually invisible to the naked eye (eye-clean) at SI1; SI2 requires careful selection.
- I1, I2, I3 (Included) Inclusions visible to the naked eye. Generally not recommended for engagement rings.
For most buyers, VS2 or SI1 is the ideal range eye-clean stones that look flawless in real life but don't carry the premium of VVS or Flawless grades. The difference between VS2 and VVS1 is only detectable under a loupe; on a finger, in any lighting condition, nobody will ever see it.
One important note: for step-cut diamonds like the emerald cut, prioritise VS1 or above. The large, open facets of step cuts make inclusions more visible than in brilliant cuts.
7. Cut Grade
Cut grade is only assigned to round brilliant diamonds on IGI certificates. It's graded as Excellent, Very Good, Good, Fair, or Poor, and it's the single most important factor in how a diamond looks.
Cut grade encompasses three components:
- Brilliance The amount of white light reflected back to the viewer
- Fire The dispersion of light into spectral colours
- Scintillation The sparkle pattern when the diamond or light source moves
Always choose Excellent cut. A well-cut diamond of G colour and VS2 clarity will outperform a poorly cut diamond of D colour and FL clarity in terms of visual impact. Cut is the one grade where you should never compromise, regardless of budget.
For fancy shapes (oval, pear, emerald, cushion, etc.), IGI does not assign a formal cut grade. Instead, look at the polish and symmetry grades, and assess the length-to-width ratio for the shape you're considering.
8. Polish
Polish refers to the smoothness of the diamond's facet surfaces. Graded Excellent, Very Good, Good, Fair, or Poor. Look for Excellent or Very Good anything below Good can affect how light enters and exits the stone.
9. Symmetry
Symmetry refers to the precision of the diamond's facet arrangement how well the facets align and mirror each other. Graded Excellent, Very Good, Good, Fair, or Poor. As with polish, look for Excellent or Very Good.
For round brilliants, the combination of Excellent cut, Excellent polish, and Excellent symmetry is sometimes called a "Triple Excellent" or "3Ex" stone the highest possible combination of grades for a round diamond.
10. Fluorescence
Fluorescence describes how the diamond reacts to ultraviolet (UV) light. Graded as None, Faint, Medium, Strong, or Very Strong, with a colour (usually blue).
Fluorescence is one of the most misunderstood aspects of diamond grading. Here's what you need to know:
- In normal lighting conditions, fluorescence has no visible effect on most diamonds
- Strong blue fluorescence can occasionally make a diamond appear slightly hazy in direct sunlight this is rare but worth knowing
- For G–H colour diamonds, faint to medium blue fluorescence can actually make the stone appear slightly whiter a minor benefit
- Diamonds with fluorescence are often priced lower than equivalent non-fluorescent stones, which can represent good value
For most buyers, None to Faint fluorescence is the safest choice. Medium fluorescence is generally fine. Strong or Very Strong fluorescence warrants a closer look at the specific stone.
11. Proportions Diagram
The certificate includes a diagram showing the key proportions of the diamond: table percentage, depth percentage, crown angle, pavilion angle, and girdle thickness. These proportions determine the cut quality of the stone.
For round brilliants, the ideal proportions are:
- Table: 54–58%
- Depth: 61–62.5%
- Crown angle: 34–35°
- Pavilion angle: 40.6–41°
- Girdle: Thin to slightly thick
If the cut grade is Excellent, the proportions will already fall within the optimal range you don't need to check each figure individually.
12. Clarity Diagram (Plotting Diagram)
The certificate includes a diagram of the diamond showing the location and type of any inclusions. Inclusions are marked with standard symbols clouds, feathers, crystals, needles, etc. and their positions are mapped on both the top (table) and side (pavilion) views of the stone.
This diagram is particularly useful for SI1 clarity stones, where the position of inclusions matters. An SI1 stone with inclusions near the edge of the table (where they'll be partially hidden by a prong) is a better choice than one with inclusions directly in the centre of the table.
13. Lab Grown Origin Statement
IGI certificates for lab grown diamonds include a clear statement confirming the stone is laboratory grown, along with the growth method either CVD (Chemical Vapour Deposition) or HPHT (High Pressure High Temperature). This is the definitive confirmation that your diamond is lab grown, not mined.
Both CVD and HPHT produce diamonds of equivalent quality. The growth method has no bearing on the diamond's appearance, durability, or value.
Red Flags: What to Watch Out For
Knowing how to read a certificate also means knowing when something doesn't add up. Here are the red flags to watch for:
- No certificate at all Never buy a diamond without an IGI or GIA certificate. An uncertified stone has no independently verified quality grades.
- Certificate from an unknown laboratory Some retailers use in-house or obscure grading labs with inconsistent standards. Only IGI and GIA are universally accepted for lab grown diamonds.
- Certificate number not laser-inscribed If the certificate number isn't inscribed on the girdle, you can't verify the certificate matches the stone. Ask why.
- Grades that seem too good for the price If a D/FL/Excellent stone is priced significantly below market, the certificate may not match the stone, or the grading may be from a non-standard laboratory.
- No lab grown origin statement A certificate for a lab grown diamond should explicitly state it is laboratory grown. If it doesn't, ask for clarification.
How to Verify Your IGI Certificate Online
Verifying your certificate takes less than a minute:
- Go to igireport.igi.org
- Enter the report number from your certificate
- The IGI database will return the full details of the graded stone
- Confirm the details match your certificate exactly carat weight, colour, clarity, cut, and measurements
We recommend doing this before completing any diamond purchase, and again when your ring arrives. At Unii Jewels, every stone's certificate number is laser-inscribed on the girdle, making verification straightforward.
Frequently Asked Questions
Does an IGI certificate add value to a diamond?
The certificate itself doesn't add monetary value it verifies the value that's already there. An uncertified diamond isn't worth more; it's simply unverified. Certification gives you confidence in what you're buying and makes the stone easier to insure and resell.
Can I get my diamond re-certified?
Yes. You can submit any diamond to IGI or GIA for grading at any time. This is useful if you've inherited a stone, purchased one without a certificate, or want a second opinion on an existing certificate.
Does the certificate expire?
No. An IGI certificate doesn't expire. The grades assigned to a diamond are permanent a diamond's physical properties don't change over time.
Is a higher clarity grade always better?
Not necessarily. For most buyers, VS2 or SI1 is the optimal clarity grade eye-clean and excellent value. Paying for VVS or Flawless clarity is paying for a distinction that's only visible under magnification. The exception is emerald and asscher cuts, where VS1 or above is recommended due to the visibility of inclusions in step-cut facets.
What's the difference between a lab grown and natural diamond certificate?
The grading criteria are identical the same 4Cs, the same scales, the same assessment process. The key difference is that a lab grown diamond certificate includes a statement confirming the stone's laboratory origin and growth method (CVD or HPHT). This is a legal requirement for disclosure in most markets.
Shop IGI Certified Lab Grown Diamonds at Unii Jewels
Every diamond in the Unii Jewels collection is IGI certified, with the certificate number laser-inscribed on the girdle for easy verification. We only work with stones graded Excellent cut (for round brilliants), G–H colour, and VS2 or above clarity so you can shop with confidence knowing every ring meets a consistent quality standard.
Browse our collections:
- All Engagement Rings our full collection of IGI certified lab grown diamond rings
- Solitaire Engagement Rings timeless single-stone designs
- Halo Engagement Rings maximum sparkle and visual impact
- Oval Engagement Rings the most popular shape of 2026
- Emerald Cut Engagement Rings architectural step-cut elegance
- Bezel Set Engagement Rings sleek, secure, and modern
- Best Sellers our most loved pieces
