What is a diamond certificate?
A diamond certificate is a document produced by a diamond laboratory that provides in-depth detail about a diamond such as clarity, colour, cut, carat, florescence, polish grade, symmetry and more. Diamond certificates do not ascribe a value to a stone as they are for authentication, identification and/or educational purposes. You can also have your diamond laser inscribed to link it back to the certificate or to write a personalised message.
Diamond grading is a subjective task due to the non-standardised nature of diamonds. Whilst diamond grading is subjective in nature, there are recognised standardised methodologies in place internationally to reduce subjectivity.
Grading is intended to quantitatively and qualitatively describe a diamond’s unique characteristics so that any diamond can be identified based on its own diamond grading report. Grading can only be carried out before a diamond is set. It does not give any value for a diamond, however it is the main tool used to determine the value of a diamond in the marketplace.
How are diamond graded/ certified?
Each diamond laboratory will have differences in process or technical machinery that determines how the diamond is graded. Generally, the diamond must be unset (loose) and free of any distinguishing marks or inscriptions before the grading process. The diamond is then weighed on a highly sensitive scale and given a carat weight. An optical scanning device or manual measuring instrument is then used to determine the stone's proportions and angles.
The clarity and finish of a diamond is determined by the laboratory technician under a microscope. Any internal or surface imperfections (called inclusions) are plotted on a graph. This graph can be used to identify a stone much like a fingerprint can identify a person.
The colour and florescence (what colours the stone throws under UV light) are measured in a controlled lighting environment. The stone is compared to a master stone set laid out in a row and the colour grade is determined. A UV light is then shone on the stone to determine the fluorescence, if any, and to what degree.
Many laboratories will put a diamond through this process multiple times to attain the most accurate grade possible. After the grading is done, optional processes like laser inscribing are then performed.
Which diamond laboratory should I use?
The JAA recognises independent grading laboratories that work to internationally recognised and respected grading rules and guidelines. Any diamond grading laboratory needs to be independent of the diamond selling process, thereby transparent and free of conflict of interest.
The JAA monitors the international diamond grading "landscape" and recognises the following diamond grading laboratories (listed alphabetically)*:
* Due to ongoing monitoring of Diamond Grading laboratories this list is subject to change over time and will be updated as and when required. JAA recognition is based on the information currently available however it advises consumers to always do their own research. A laboratory is only deemed independent if it is not in any way involved in the sale of diamonds.
Are diamond certificates and valuations certificates the same thing?
No. Valuations are documents that provide detailed descriptions of jewellery and ascribe it a value based on certain market conditions. A diamond certificate is a laboratory report that sets out the physical specifications of a diamonds such as carat weight, cut, treatment, and clarity without a judgement of value.
International Diamond Grading Scales
Image: International colour grading scale for diamonds
Image: International carat weight grading scale for diamonds
Image: International cut grading scale for diamonds.
Image: International clarity grading scale for diamonds.