Lab-grown diamonds are graded on exactly the same 4Cs framework as mined diamonds. Cut, colour, clarity, and carat. The scales, the terminology, and the grading standards are identical. The difference is that lab-grown diamonds are assessed by IGI rather than GIA in most cases. This guide explains each C as it applies to choosing a lab diamond for your engagement ring.
A diamond's cut grade is the most controllable quality factor because it is determined by the cutter, not by geology. For lab-grown diamonds, where colour and clarity can be engineered to high standards, cut quality is the variable that most distinguishes an excellent stone from an average one.
IGI grades diamond cut on a scale from Excellent through Very Good, Good, Fair, and Poor. Moissanite by Design recommends Excellent cut as a minimum for round brilliant lab diamonds. For fancy shapes, Very Good is acceptable given that standardised cut grading applies less precisely to non-round shapes.
Lab-grown diamonds are graded on the same D-to-Z colour scale as mined diamonds. D is completely colourless. Z shows a visible yellow tint. The scale was developed by GIA and is used universally across the industry, including by IGI for lab-grown stone certification.
No visible colour tint under standard grading conditions. The highest grades available. Recommended for platinum and white gold settings. Carries a premium over near-colourless grades.
Colour tint only visible under magnification or direct side-by-side comparison with higher grades. The most popular range for engagement rings. Excellent balance of quality and value.
Slight warmth visible to a careful observer in certain lighting. Pairs well with yellow or rose gold settings. A practical choice for buyers maximising size or clarity at a given budget.
Lorna recommends D-H for platinum and white gold settings. J-K can work well in yellow or rose gold where the warm undertone of the gold complements rather than contrasts with the stone's colour.
Clarity measures inclusions (internal characteristics) and blemishes (surface characteristics). Lab-grown diamonds can achieve high clarity grades because the growth environment is controlled, but this does not mean all lab diamonds are flawless. The same range of clarity grades exists in lab-grown stones as in mined stones.
Eye-clean is the practical standard for engagement rings. A diamond does not need to be FL to be beautiful. VS2 or SI1 at excellent cut and good colour will outperform FL at poor cut in any lighting condition.
Moissanite by Design — Clarity GuidanceFlawless or internally flawless under 10x magnification. The highest clarity grades. For lab-grown diamonds these carry less rarity premium than in mined stones.
Very very slightly included. Visible only under magnification to a trained gemologist. Eye-clean. Excellent choice for buyers who prioritise clarity documentation.
Very slightly included. Difficult to see under magnification. Eye-clean. The sweet spot for most buyers combining high clarity with good value.
Slightly included. Inclusions visible under magnification. SI1 is typically eye-clean and offers significant value relative to VS grades. The most budget-efficient clarity choice for most briefs.
Inclusions may be visible to a careful naked eye in direct lighting. Requires inspection before purchase. Lorna always confirms eye-clean status before recommending an SI2 stone.
Moissanite by Design will not recommend a stone that is not eye-clean regardless of budget. Visible inclusions in a finished ring are unacceptable at any price point.
Carat is weight, not size. A 1ct diamond weighs 0.2 grams. Two diamonds of identical carat weight can appear different sizes depending on how the weight is distributed across the stone's cut geometry. A well-cut 1ct diamond will appear larger than a deep-cut 1ct diamond even though both weigh the same.
Lab-grown diamonds allow buyers to access significantly more carat weight at a given budget than equivalent mined stones. This is the most frequently cited reason buyers choose lab-grown.
Approximately 6.4-6.5mm diameter at Excellent cut. The most popular size for engagement ring centre stones. Substantial visual impact at an accessible price in lab-grown.
Approximately 7.4mm diameter. A noticeable step up in visual presence. Widely achievable in lab-grown at a budget that would only reach 1ct in mined diamond.
Approximately 8.0-8.1mm diameter. A genuinely large stone. In lab-grown, 2ct is accessible at a price many buyers associate with 1ct mined stone quality.
Oval, pear, emerald, and cushion cuts create different visual impressions at equivalent carat weights. Elongated shapes tend to appear larger than round brilliant at the same weight.
The diameter of a stone as viewed from above, face-up, is the most relevant measurement for visual impact in a ring. Lorna always provides face-up dimensions alongside carat weight.
At a given budget in lab-grown diamond, the best strategy is usually to prioritise cut (Excellent), accept G-H colour, and choose VS2 or SI1 clarity. This maximises carat weight while maintaining quality across all visible characteristics.
The International Gemological Institute is the standard certification body for lab-grown diamonds. Every IGI certificate documents the stone's cut grade, colour grade, clarity grade, carat weight, and growth method (HPHT or CVD). The certificate provides independent third-party verification of all four quality characteristics.
Moissanite by Design provides the IGI certificate with every lab diamond commission. Lorna selects stones based on how the 4Cs interact together at the client's budget, not based on any single grade in isolation.
Read the full guide to what a lab-grown diamond is, learn about IGI certification in detail, or send your brief to Lorna for personalised stone selection.
Are lab-grown diamonds graded the same way as mined diamonds?
Yes. Lab-grown diamonds are graded on the same 4Cs framework, the same D-to-Z colour scale, and the same clarity grading scale as mined diamonds. IGI uses the same standards as GIA.
What colour grade should I choose for a lab-grown diamond?
For platinum or white gold settings, D-H is recommended. For yellow or rose gold settings, up to J can work well. G-H near colourless offers excellent value for most buyers.
What clarity grade is eye-clean in a lab-grown diamond?
VS2 and SI1 are typically eye-clean. VS1 and above are reliably eye-clean. Moissanite by Design confirms eye-clean status before recommending any stone regardless of its stated clarity grade.
Does IGI grade lab-grown diamonds the same way as GIA grades mined diamonds?
IGI uses the same 4Cs framework and terminology as GIA. The grading standards are comparable, though some in the industry consider GIA grading slightly more conservative. For lab-grown diamonds, IGI is the accepted industry standard.
What is the best 4Cs combination for a lab-grown diamond engagement ring?
Excellent cut is the priority. G-H colour and VS2 or SI1 clarity at the largest carat weight your budget allows is the most effective strategy for maximising visible quality in a finished ring.
Lorna guides every client through IGI stone selection personally. Share your brief and budget for a personalised stone recommendation.
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