Diamond Grading Process

Step 1

Carat Weight

The first stage in diamond grading is weighing the diamond. Carat weight is the standard weight unit for gemstones. Diamond grading scales are calibrated to four decimal places to ensure accuracy. Carat weight is reported to two decimal places.

Measurements

The diamond’s measurements are established using a gemstone-specific optical measuring device. The scanner creates a 3D digital sculpture of the faceted stone’s total geometry, including all proportions, measurements, and facet angles. Key measurements are printed on the diamond’s grading report.

Step 2

Color and Fluorescence Grading

Diamond color is graded in a standardized viewing environment. IGI gemologists analyze color in the D to Z color range on the diamond quality scale with the diamond placed upside down, viewed through the side, to facilitate a neutral view. Grading color from the top is not practical because of three factors which may influence color appearance in normal viewing.

• The diamond’s shape
• The way the diamond was cut
• The presence of fluorescence

Color is graded using calibrated master color stones. The diamond grading process involves multiple graders submitting opinions independently, while uniformly applying the diamond grading scale.

Fluorescence Grading

Fluorescence is a measure of the diamond crystal’s reaction to ultraviolet (UV) light. Around 35% of all diamonds emit fluorescence when subjected to UV light. If fluorescence is present, the diamond grading scale chart is applied and the strength and color of the fluorescence are recorded.

Step 3

Clarity and Finish Grading

IGI grades clarity according to internationally accepted standards at 10X magnification, according to the visibility, size, number, location, and nature of internal and surface characteristics at that magnification. Diamonds with characteristics which are immediately obvious or noticeable are likely candidates for the lower grades, whereas diamonds with characteristics which are minor, minute, or extremely difficult upon initial analysis at that magnification may qualify for the higher grades. This detailed assessment forms a crucial part of the diamond quality evaluation.

Plotting

The gemologist will use a step-by-step wedge technique, examining the diamond in segments, to note the location and nature of all relevant clarity characteristics. A map of the diamond’s internal and external clarity characteristics, as observed at 10X magnification, is provided for purposes of information and identification on a diagram representative of the diamond’s shape and faceting style.

Step 4

Cut Grading

IGI assesses craftsmanship components for all diamonds according to the diamond quality scale for each shape – with cut grading and optional light performance reports for round brilliant cuts – and a cut grading option for fancy shaped diamonds.

Round Brilliant Cut Diamonds

IGI assesses all round brilliant cut diamonds in the areas of polish, symmetry, and proportions. The top cut grade a round brilliant diamond can earn is Excellent-Ideal. The overall proportions, measurements, and facet angles determine the Cut Grade. If the polish and symmetry assessments are lower than the grade according to overall proportions, they may cause the overall cut grade to be lowered, in accordance with the diamond grading scale chart, also known as a “4Cs chart.”

• See the Cut Grade Chart for round brilliant cut diamonds

Light Performance Report for Round Diamonds

Diamonds of the same shape, size, and cut grade can have different visual tendencies. For this reason, IGI offers a light performance report option for round diamonds displaying top optical performance, which provides a primary Light Performance score and scores for three observable sub-components: Brightness, Fire, and Contrast.

• See a video overview of the Light Performance Grading process
• See and download the IGI Light Performance Cutting Guidelines

Cut Grading for Fancy Shaped Diamonds

IGI assesses all fancy-shaped diamonds in the areas of polish, symmetry, and proportions. All shapes and colors will have craftsmanship grades for polish and symmetry noted on the grading report. Cut grading for fancy shapes ranges from Excellent to Poor based on the process and parameters linked below and is optional.

• Scroll down this page for a video overview of the Fancy Shape Cut Grading process
• See and download the IGI Fancy Shape Cut Grading Guidelines for Excellent

Step 5

Verification

In the areas of color and clarity analysis, multiple gemologists take the diamond through the grading steps and provide opinions according to the diamond grading scale, completely independent from the others. Color and clarity grades are only finalized when a consensus is reached.

Step 6

Grading Controls

Between each grading step, a diamond returns to central control, the assignment to various gemologists is completely random. Every diamond is electronically tracked so that central control knows its location at any time and may review each step in the process leading to its complete assessment according to the IGI grading scale.

Step 7

Laser Inscription

IGI’s LASERSCRIBE SM, combined with the standard of excellence and recognition of IGI’s Diamond Grading Reports, assures you of both the quality and identification of your diamond. In fact, every laboratory-grown diamond IGI grades will have an inscription identifying laboratory-grown origin automatically applied.

For natural diamonds, the laboratory will apply laser inscriptions by owner’s request, typically the diamond’s grading report number. If the diamond belongs to a brand or specific store, the owner may also have a logo inscribed.

Step 8

Report Printing and Security

Diamond grading reports are printed on advanced security paper with no less than five security features. These include tear-proof paper, micro printing, holographic, and other security features. The diamond is weighed, verified as matching the report by central control, cleaned, and prepared for return to its owner along with the new diamond grading report, which is placed in a protective sleeve or binder.

Step 9

Digital Grading Report Posted

Once the diamond and report have left the diamond grading laboratory premises, a digital copy of the report will be posted online. This report is accessible using the IGI Verify Your Report feature. The QR (Quick Response) code on the printed grading report can also be scanned by a QR code reader and will take the user to the corresponding grading report, posted online.