Lab Grown Diamonds 4C: GIA & IGI
The 4C grading system was created by GIA. IGI adopts the same 4C framework, yet notable differences exist in certificate content, market positioning and grading strictness.
Basic Definition of the 4Cs
1. Carat: Unit for diamond weight. 1 carat = 0.2 grams. Larger weight means higher value. Certificates show weight to two decimal places. GIA and IGI use identical weighing standards.
2. Color: Colorless diamonds are graded from D (highest, totally colorless) to Z (light yellow / light brown). D-F: Colorless, G-J: Near Colorless, K and below: Visible yellow tint to the naked eye.
3. Clarity: Evaluates internal inclusions and surface blemishes under 10×magnification. Grades: FL > IF > VVS1/VVS2 > VS1/VS2 > SI1/SI2 > I1/I2/I3. Fewer and less noticeable inclusions equal a higher grade. A clarity plot on the certificate marks inclusion locations.
4. Cut: The only human-controlled factor that determines diamond brightness, fire and scintillation.
Round brilliant grades: Excellent, Very Good, Good, Fair, Poor.
For fancy shapes (Radiant, Asscher etc.), neither GIA nor IGI issues an overall Cut grade; only Polish and Symmetry are listed.
GIA (Gemological Institute of America)
Position: The benchmark for natural diamonds, inventor of the 4C standard, non-profit institute, most recognized for large natural diamond collection and trading.
Natural diamond certificates: Full individual 4C grades, including clarity plot, proportion diagram, fluorescence, polish and symmetry, for loose stones.
Key Update: New GIA LGDR Certificate for lab grown diamonds (effective Oct 2025)
GIA no longer lists discrete color grades such as D/E/F or clarity grades like VS1/SI1. Only two broad tiers are provided: Premium: D-F color, VVS~VS clarity, Standard: G-J color, SI clarity.
Detailed separate 4C subgrades are replaced by range grouping. Small-sized lab grown diamonds may still be issued old-format certificates with complete 4C details.
IGI (International Gemological Institute, Antwerp, Belgium)
Position: Globally dominant certificate provider for lab grown diamonds; world’s largest independent gem lab with long-standing focus on lab grown diamond industry.
Both natural and lab grown diamond (HPHT/CVD) certificates retain full 4C breakdown: full D-Z color scale, FL-I3 clarity scale, cut grade, clarity plot, diamond proportions, fluorescence, growth method and post-treatment status. Loose stones are laser inscribed on the girdle with certificate number plus "lab grown".
Global labs in Antwerp, Shanghai, Mumbai, etc. The Shanghai IGI lab applies stricter grading criteria.
The Difference Between GIA & IGI
| Item | GIA | IGI |
| Origin of 4C System | Inventor of the 4C system | Adopts GIA’s 4C framework |
| Natural Diamond Certificate | Full breakdown of 4C grades. Widely regarded as the strictest; top choice for high end natural diamonds | Complete 4C grades with solid recognition, though less market circulation than GIA |
| New Version Lab Grown Diamond Certificate | Fine individual 4C grades removed since Oct 2025; only two tiers: Premium / Standard | Retains full complete 4C grading with clarity plot. Most popular for foreign trade independent websites |
| Grading Rigor | Overall the strictest. Industry consensus: the same stone often receives a grade 0.5–1 level lower from GIA | Slightly more lenient. The Shanghai IGI lab has tightened standards, narrowing the gap |
| Market Focus | Natural diamonds, high-end collections and traditional jewelry markets | Leading global certificate for lab grown diamonds; widely used in loose stone wholesale, cross-border e-commerce and overseas retail |
| Fancy Shape Diamonds | No overall Cut grade; only Polish and Symmetry listed | No overall Cut grade; only Polish and Symmetry listed |
| Certificate Verification | Verifiable on official website, with laser inscription | Verifiable on official website. Certificate number laser inscribed on girdle for easy verification |
