IGI vs GIA Certification : What is the difference?


When buying a diamond, the most important assurance is that it comes with a certificate issued by an internationally recognized gemological authority. It is a form of validation by professionals in the field of the quality of your diamond. Leading authorities include the Gemological Institute of America (GIA), American Gemological Society (AGS) and International Gemological Institute (IGI). That being said, does it matter which certificate, and is one better than the other?

GIA is one of the foremost gemological authorities in the world. Established in 1931, it has entrenched itself as a key player in the field of diamond grading. The convention of 4Cs was developed by GIA and it has since been a gold standard in diamond grading. AGS was established in 1934, initially to cater to the United States domestic jewelry market, serving as a market standard. It soon expanded and is now one of the key institutes worldwide. They utilize their own numeric scale of diamond grading based on the grading standard developed by GIA. IGI was established in 1975 in Antwerp, the diamond capital of the world. Since then it has stood against the well-established institutes like GIA and AGS, who had already accumulated 40 years of followings.

Joseph Lee from Diamond Screener took an empirical approach to compare the certification standards of the gemological institutions, using dual certified diamonds (GIA and IGI) from the inventories of Blue Nile and James Allen.
The study is based on 29 dual certified stones, and the grading of cut and color was analysed, yielding 58 comparisons. 32 comparisons showed the same grading standards, while GIA was stricter on 11 occasions and IGI was stricter on 15 occasions. Of these discrepancies in grading, the differences were only a single unit apart, which was an acceptable deviation, with the exception of two comparisons. One of which was that GIA graded the color of the diamond as ‘I’, while IGI graded it a ‘G’, two units apart, where both grades fall under the ‘near-colorless’ band. On the second occasion, GIA graded the clarity of a diamond as ‘VVS1’, while IGI graded it as ‘VS1’. The conclusion drawn from this study is that the grading was consistent between the two gemological laboratories and differences were mainly one unit apart (except for two comparisons).


Another study came from Rapaport group, a network of companies providing services supporting fair and transparent dealings in the diamond market. They compared grading standards from various grading labs. To conduct this study, they sent 10 diamonds to six grading labs worldwide. With the grading report, they normalized the results on a ‘quality index’, where the lower the number, the less lenient they are. Results showed that GIA was the strictest (at 14.8), with IGI trailing behind by one basis point (14.9). Median was at 15.9, while the ceiling was at 19.8.

Apart from that, the diamonds’ pricing was extrapolated from similar diamonds with similar quality on the Rapnet database. Data showed that GIA would yield the most revenue (i.e. being sold at the highest price), while revenue for IGI would rank fourth. This showed that while grading is consistent with GIA, their pricing is significantly lower than what the quality would deserve. This highlights a discount for the consumers where costs are borne by the jewelers.


In conclusion, while diamond grading could be a somewhat subjective field, variations do not stray much among these laboratories. The analysis of multitudes of grades of gems have only made the standards more consistent. In fact, these gemological institutes have only made buying a diamond more transparent than ever.

Research from and Empirical Perspective

Key Gemological Laboratories

Research from an Experimental Perspective


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