A question that is often asked of me is 'What are the differences between diamond certificates? Even more specific, 'What is the difference between a Tiffany & Co. Diamond Certificate and a GIA Certificate?' I have seen hundreds of Tiffany & Co. diamonds however I am not a gemologist. This article has been written from personal observation of hundreds of diamonds, including widely accepted information that jewellers have shared with me.
This is an important question to cover because diamond certificate grading is not absolute. What this means is that the exact same diamond sent to a different laboratory can often come back with a different grade in colour, cut and clarity.
This article briefly covers the 4 labs commonly used for grading diamonds and how the grading slightly varies between each one.
1. GIA Diamond Certificate
GIA stands for the Gemological Institute of America. Founded in 1931 this lab is the most widely known and respected diamond grading laboratory in the world. They are known for having strict and consistent grading for colour and clarity. The only area where they are said to have a broader measure on their grading is cut. GIA has a slightly wider tolerance of an excellent cut diamond than AGS.
2. Tiffany & Co. Diamond Certificate
Tiffany & Co. used to use GIA to certify all their diamonds. However about 30 years ago they started to do their own in house grading. Their explanation for this, was that they thought that GIA was too soft on grading. It is widely accepted that Tiffany & Co. grade at least as good as GIA. In fact is has been stipulated that if a diamond is on the border of a colour grade, ie an F-G colour, Tiffany & Co. will be slightly stricter than GIA. Tiffany & Co. do not provide a clarity map on their certificates. As all diamonds sold are assessed for their beauty and being eye clean, presumably it wouldn't look attractive to have a plot of inclusions on their diamond certificate.
3. AGS Diamond Certificate
AGS stands for American Gem Society. A relative newcomer to diamond grading, this lab started issuing Diamond Certificates in 1996. They are also a highly regarded laboratory and generally considered on pah with GIA. Anecdotally they have been seen to be slightly softer on colour by about 1 grade but this is not absolute. They are the only laboratory to give an ideal cut diamond grade. An ideal cut diamond AGS 000 is considered the most perfectly cut diamond. These diamonds exhibit the rare phenomenon of perfect symmetry of hearts and arrows and sparkle most brilliantly. As this grade falls within the parameters of an excellent cut diamond graded by GIA, they can be considered stricter on cut than GIA.
4. EGL Diamond Certificate
EGL stands for the European Gem Laboratory. There are various branches of EGL known as EGL-USA, or EGL-International. EGL is renowned for being much softer on grading than GIA, AGS and Tiffany & Co. They also have no consistency across their laboratories. Colour and Clarity grades of EGL can be 2 to 3 colours, clarity or cut grades off. So if you think you are paying for a G coloured, VS2 diamond, excellent cut diamond you are in fact getting a J Coloured, SI2, good cut diamond from a more reputable laboratory.
Not a recommended laboratory.
As already mentioned this is a very brief overview of the 4 main certificates I have seen. There are other grading laboratories and many other in house certificates, however these 4 certificates are the 4 most commonly bought up in questions to me.
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