Our Grading System

How does SGL grade diamonds ?

People from all over the world send their diamonds to the SGL Laboratory for grading and analysis. Our clients put their business in our hands and their trust in our expertise – and we are extremely careful with both.

Diamond Grading Process

From the moment a diamond is entrusted into our hands, until the moment it is returned back to the client, it is handled and assessed with the utmost care, security and expertise by our team of highly-trained gemologists and support staff. Using state of the art instruments and industry respected grading procedures, the SGL laboratory identifies, assesses and grades each diamond according to the strict standards to which we are committed.

Eight-Step Grading Process

1. Registration

As soon as a diamond is submitted to our laboratory, it is weighed and measured, and then assigned with an identification number. This identification number replaces all client information in order to ensure unbiased, objective grading. The client is provided with a receipt stating the identification number, initial weight and the measurements of each diamond submitted.

2. Identification

Each diamond is scanned by DiamondSure™ - and, when necessary, by DiamondView™ - machines which confirm that the diamond is in fact an authentic, natural diamond.

3. Weighing and Measuring

The diamond is then weighed and measured twice more with our state of the art measurement equipment. SGL’s measurement devices are located in a controlled environment and calibrated at minimum, twice a day.

4. Cut Grading

The measurements taken by the measurement devices, along with a visual assessment of the diamond’s girdle and culet sizes, are used to calculate the diamond’s cut grade. There are six cut grades ranging from excellent/ideal to unusual. The diamond is then visually examined to substantiate the accuracy of the cut grade. The diamond is then visually evaluated for optical symmetry to determine whether it displays a “hearts & arrows” pattern.

5. Clarity Grading

The diamond is analyzed at 10X magnification by a minimum of three gemologists to determine its clarity grade based on the number, type, position and size of the clarity characteristics displayed on the stone. Each gemologist examines the stone without knowledge of the previous gemologist’s findings in order to attain the most accurate clarity grading.

6. Color Grading

Each diamond’s color is graded by at least three gemologists in a controlled environment. The color grade is based on a scale of D (colorless) to Z (light amounts of color).

7. Certificate Issuance

After the grading process is completed, your diamond reaches our documentation station, where we print a Diamond Grading certificate or Diamond Précis indicating all grading results. At this point, the grading results can be accessed electronically by the client through our online account management system.

8. Laser Inscription

Only after the first seven steps of the grading process have been completed is the diamond sent for laser inscription. If a Diamond Précis was ordered for the diamond, it will have the identification number laser-inscribed on its girdle. The inscription number is the same as the ID number on the diamond’s certificate. For a small additional fee, diamonds receiving an SGL Diamond Grading certificate may also have their ID number laser inscribed on the its girdle. Additionally, all diamonds may receive an inscription of a specific brand or company name or a personal message for the customer. (This service is considered as extra service and not include in the SGL basic grading service pack.)