In the realm of coloured gemstones and diamonds, it is crucial, now more than ever, to have an independent evaluation of the stones. This assessment serves a principal purpose: to determine if any treatments have been applied that could impact their value. For jewellers and retailers, safeguarding against fraud and upholding the integrity of their inventory are paramount concerns. Additionally, customers often seek certificates and laboratory verifications to ascertain the value of stones, particularly for sizeable or costly pieces. Therefore, being well-acquainted with reputable laboratories and the certificates they issue is key for success.
Laboratories generally use their own proprietary methods to evaluate stones. Some discrepancies do exist between lab ratings, especially on fine colour evaluation work. However, the top seven laboratories worldwide are currently in partnership on a Laboratory Manual Harmonisation Committee (LMHC), which aims to reduce differences and move toward a true international standard.
These laboratories are:
– the CGL Laboratory, located in Tokyo, Nagoya, Osaka, Fukuoka & Kofu in Japan.
– the CISGEM Laboratory, located in Milan, Italy.
– the DSEF German Gem Lab, located in Idar Oberstein, Germany.
– the GIA Laboratory with 3 locations: Two in the USA (Carlsbad and New York) and one in Bangkok, Thailand.
– the GIT-Gem Testing Laboratory, located in Bangkok, Thailand.
– the Gübelin Gem Lab Ltd., located in Lucerne, Switzerland.
– the Swiss Gemmological Institute – SSEF, located in Basel, Switzerland.
The International Gemological Institute (IGI) is another well-reputed independent evaluator for diamonds and the Gem Research Swisslab (GRS) for coloured gemstones are not affiliated with this group, but held in high esteem like Gübelin for definitive judgements.
Which Labs to Use
For Diamond Certificates
In terms of reporting, for coloured diamonds and white diamonds alike, there is one main laboratory that issues reports on over 95% of the world’s certificated diamonds and that is the GIA. The other labs commonly in use for diamonds and coloured diamonds are IGI and once common, but less so now, HRD of Antwerp. The Argyle Diamond Mine issues a certificate of authenticity on Argyle pink diamonds to show their origins are bonafide (there is an additional premium for pink diamonds with an Argyle certificate). Their main job is essentially threefold for a coloured diamond. The first is to tell you if it is natural or treated, the second is to offer you a colour description and the third is to give you a clarity description.
You should be aware that different laboratories can offer different opinions about the same stone, especially when it comes to Origin. The key term here is opinion and that’s the term they hide behind when they make mistakes.
Armed with a little more knowledge, the next engagement ring you sell might be a with a certificated stone.
Which Labs to Use
For Gemstone Certificates
For gemstones it is slightly different. Most of the testing falls to the Swiss who have made a name for themselves in this field.
The main labs to consider here are GRS certificates, by far the biggest and most commercial; Gubelin, essential for very high value stones; SSEF, good for emeralds; AGL and GIA essential for the United States. There are lots more local laboratories that can generally tell you whether a stone is treated or not and might have an opinion on the origin of a gemstone, but any stone over a certain value will need to be accompanied by one or more of the labs listed above.
Whilst cut is secondary in a gemstone, the purpose of a Gemstone report is to tell you
a. where the stone is from
b. what treatment it has undergone, and
c. offer a colour description
There are now a few colour descriptions for coloured stones that will enhance the value of a stone dramatically. They are ‘Pigeon’s Blood’ and ‘Vivid Red’ for certificated rubies, and ‘Vivid Royal Blue’ and to some extent ‘Cornflower Blue’ for sapphires. For Emeralds it’s the presence of oils, or lack of, that will have a big influence on price, especially for Colombian stones.
Browse through our diamond collection: