What Happens Before You See the Certificate
Every IGI or GIA grading report represents hours of careful examination by trained gemologists using specialized equipment. Understanding the grading process helps you appreciate what the certificate means and why independent grading matters. Here is what happens when a diamond enters a gemological laboratory.
Step 1: Intake and Anonymization
When a diamond arrives at the lab, it is separated from any identifying information about the submitter. The gemologist who grades the diamond does not know who submitted it, what it was purchased for, or what grade the submitter hopes to receive. This anonymity is critical for objective grading.
Step 2: Weight Measurement
The diamond is weighed on a precision electronic scale to the hundredth of a carat (0.01 ct). The scale is calibrated daily. Multiple measurements may be taken to confirm accuracy. The weight recorded on the report is the actual measured weight, not a rounded approximation.
Step 3: Measurement
Using optical measuring devices, the gemologist records the diamond's physical dimensions to the hundredth of a millimeter. For round diamonds, this includes minimum and maximum diameter and depth. For fancy shapes, length, width, and depth are recorded. These measurements are used to calculate proportion percentages.
Step 4: Proportion Analysis
Using specialized equipment (like the Sarin or Helium systems), the diamond's facet angles, percentages, and symmetry are measured digitally. The proportion diagram on the report comes from this analysis. For round diamonds, the cut grade is determined by comparing these proportions against established ideal ranges.
Step 5: Color Grading
- The diamond is placed table-down on a white grading tray under standardized daylight-equivalent lighting
- The gemologist compares the diamond against a set of master comparison stones — diamonds that represent known color grades
- Multiple gemologists independently grade the color, and a consensus grade is assigned
- The process is designed to eliminate subjective bias
Step 6: Clarity Grading
- The gemologist examines the diamond under 10x magnification (the industry standard) looking for inclusions and blemishes
- The size, number, position, nature, and relief (contrast) of any characteristics are assessed
- An inclusion near the center of the table is more impactful than one near the edge
- The clarity grade reflects the overall visibility of characteristics under 10x
Step 7: Polish, Symmetry, and Fluorescence
Polish quality is assessed under magnification. Symmetry is evaluated by examining facet alignment, shape accuracy, and proportion consistency. Fluorescence is tested using UV light — the diamond's reaction (color and intensity) is recorded.
Step 8: Report Generation
All data is compiled into the final grading report with the unique report number. The diamond may be laser inscribed with this number on the girdle for identification.