Due to the small number of GIA-AGSL and GIA-EGL USA dual-certified diamonds, we only analyzed the 37 GIA-IGI dual-certified diamonds. For the James Allen set, we found 11 dual-certified diamonds (7 IGI, 1 AGSL, 2 EGL USA). For the Blue Nile set, we found 39 dual-certified diamonds (30 IGI, 7 AGSL, 2 EGL USA). We searched the inscription field of each GIA certificate for references to IGI, EGL, or AGSL. We collected GIA certificates for round diamonds listed for sale on Blue Nile (n=143058 diamonds) and James Allen (n=75624 diamonds). For two diamonds of the same carat, color, and clarity grade, an IGI certified diamond is on average 12% cheaper than a GIA certified diamond.īased on the results of the grading and pricing analyses, IGI certified diamonds potentially represent a good value opportunity.
We then conducted a comparative analysis of IGI vs. Our analysis of dual-certified diamonds suggests that IGI’s grading standards are comparable to GIA, corroborating the results of the RapNet study. We searched the inventories from Blue Nile and James Allen and identified a set of diamonds that were certified by both GIA and IGI (N=29). Rather than conduct an expensive prospective study to compare grading labs, we conducted a retrospective observational study of dual-certified diamonds. RapNet study, N=10 diamonds) that limit their ability to draw conclusions about which lab is best.
When such studies are available they often have small sample sizes (e.g. Prospective head-to-head comparisons are rare due to the cost of sending diamonds to multiple grading labs. However, there is a lack of hard data to support this claim. GIA is often held up as the gold standard of diamond grading while other labs are purported to have looser grading standards.
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