Are all grading laboratories the same?

Ever wondered if you can trust the person you’re buying from? What the paperwork they’ve provided actually counts for? Far too often people are disappointed to find that their jewellery is not of the quality that they were told when they purchased it. So how can we know who to trust and who not to trust? One of the best ways is to buy a stone that has an independent laboratory certificate. However, as the case below highlights, even this is not any guarantee.

Recently we were asked to value a diamond solitaire ring for insurance purposes. The client supplied a certificate for the central 1 carat diamond from European Gemological Laboratories (EGL) in Antwerp, Belgium. This stated that the diamond was D colour and VS2 clarity. This seemed like a reliable source, even to us. However our examination made us doubt this grading as the diamond had inclusions making it two grades lower at SI2, and the colour appeared also two or more grades away from the D colour. We started to wonder; was the diamond the same one listed on the certificate ?

Examination under the microscope showed the same EGL report number on the certificate was laser inscribed into the girdle. So it was the same stone as the certificate. We were left wondering whether it was ourselves or EGL that had graded incorrectly. Further analysis showed there was another laser inscription from the Gemological Institute of America (GIA). As GIA certificates are accessible online, we searched the inscribed number and the GIA certificate showed the diamond to be G colour and SI2 clarity – the same as we saw it.

So how can a diamond be certified by one international laboratory (EGL) as D colour, VS2 and another lab (GIA) as G colour, SI2 ? This difference could change the value of the ring by thousands of dollars.


Some investigation found that the two labs appear to have different standards. But while EGL works under separate standards to GIA, they both use the same terminology in their reports. As no one owns the rights to the diamond grading scales we’re all so used to using, they are both within their right to grade as they see fit. However, that can be both confusing and misleading.

The lesson here is that who has graded, certified or valued your diamond is as important as the grading they have given. Before you buy a diamond, do your research on which grading laboratories have the best reputation for accuracy and consistency. Insist to your jeweller that the diamonds you purchase must be graded by one of them. And remember that if a purchase price looks too good to be true, even with supporting documents, it probably is.