Carat WeightImitations and Synthetics 
Diamond Certification
Grading diamonds correctly and consistently is a skill that requires a lot of practice and patience. For this reason it is impractical to presume that everybody handling, buying or selling diamonds is equally well skilled at this. This is why grading certificates are used to identify and compare different diamonds.
It is important to understand what should and should not be included on a diamond grading report. Colour, clarity, cutting style (shape), weight precise to 1/100th of a carat, exact measurements precise to 1/100th of a millimeter, proportions and symmetry details, fluorescence, any artificial treatments applied to the diamond, possibly a cut grade, a diagram showing locations of the inclusions and extra remarks such as laser inscriptions on the girdle should be included. The name and address of the grading lab, date and the number of the report should also be included. Estimated price should not be included. The certificate serves to prove the identity of the stone, information in it will not change over the years and is easy to confirm by grading the diamond again. Information such as price, on the other hand, changes over time, location, and situation. A diamond certificate is not an appraisal and does not guarantee any specific price.
Since a diamond certificate is just like an official personal identification document, treat it as such. This means that first and foremost it has to come from a reputable source. There are many organizations and private entities in the world that are qualified to grade diamonds and other gem stones. This does not mean that all of them are actually capable of giving their unbiased opinion. For example, a graduated gemologist that works for a specific jewellery store can be expected to claim that the diamonds at that store are a grade or two higher to improve the sales. There are several recognized independent gemological grading laboratories that are trusted with providing consistently correct grading results. The most popular are GIA (Gemological Institute of America), AGSL (American Gem Society Laboratories), EGL (European Gemological Laboratory) and HRD (Hoge Raad voor Diamant, Belgian for Diamond High Council). GIA and AGSL are most popular and trusted in North America, while HRD is considered the most desireable in Europe. While there are other reputable grading labs around, only the above ones proved to be consistent and accurate in their reports, so much that diamonds accompanied by their reports will cost slightly more than diamonds graded by other laboratories.
AGSL is well known to have the most comprehensive cut grading system of all the labs which is why if you are looking for the best cut diamonds you will very likely see a lot of Ideal cut diamonds graded by AGSL. While GIA recently started to provide cut grade too, their system is based on only 5 possible grades, while AGSL ranks cut according to 11 grades. For this reason an Ideal (0) AGSL graded diamond is perceived to be of higher quality than an Excellent GIA graded, even though both may be equally well cut and stunning.
The layout of the certificates is standardized in each grading lab and you can view sample certificates online on the grading labs' websites. You can follow the links to sample reports by GIA, EGL and AGSL to see how each would look like. Most laboratories have several certification options available that differ in the amount of detail the document includes. They also tend to change the layout of the certificates every few years. In any case, every lab keeps the information about every graded stone on file and you can check the validity of any certificate by contacting the laboratory directly.
Carat WeightImitations and Synthetics
