Diamond Cut Grading

1. Round Brilliant Cut Diamonds

Assessments: Polish, Symmetry, Proportions and Light Performance

IGI assesses 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.

Light Performance Report

Diamonds of the same shape can have different visual tendencies. For this reason IGI will issue a light performance report for round diamonds displaying top optical performance, which provides an easily understood breakdown of their quantifiable beauty components.

• Light Performance: The overall strength of light return (versus leakage).
• Brightness: All reflected and refracted white light
• Fire*: Dispersed light seen as flashes of color
• Contrast: Balance and intensity of bright and dark areas

Note that light performance analysis is based on external proportions and does not account for dense clarity characteristics/reduced transparency.

The Ideal-Scope Representation, generated with ray-tracing software, conforms to the diamond’s specific parametric averages, permitting further verification and analysis of its fundamental light behavior in the Ideal-Scope, a scientific light performance assessment tool.

See the video tutorial below for more information

Round Brilliant Methodology

IGI researchers used ray-tracing software to analyze light performance for round brilliant diamonds spanning thousands of proportions sets and 18 table sizes. Parameters judged to have Exceptional performance, overall, were isolated and further assessed to arrive at four summary calculations: Light Performance, Brightness, Fire* and Contrast.

*Fire is only seen in conducive lighting

Click to see Light Performance Manual, Video Tutorials and FAQ

2. Fancy Shaped Diamonds

Assessments: Polish, Symmetry, Craftsmanship and Light Return

Fancy Shape Methodology

 IGI grades the cut of fancy shaped diamonds on a scale ranging from Excellent to Poor, assessing polish, symmetry, proportions, and additional craftsmanship requirements in a four-step process.

1. Polish and symmetry grading
2. Proportions qualification
3. Additional craftsmanship requirements
4. Light return grading

Click to see Process for Fancy Shape Cut Grading

Fancy Shape Cut Grading: Four Step Process

Step 1: Polish and symmetry grading

• Diamonds earning a minimum of Very Good in both areas become candidates for an overall cut grade of Excellent

Step 2: Proportions qualification

• Fancy shape cut quality cannot be graded using proportions (alone) but IGI has published parameters historically observed to produce the most positive beauty components in different shapes
• Diamonds within those parameters remain candidates for Excellent

Step 3: Additional craftsmanship requirements

• Shape specific requirements designed to analyze bow-ties, girdle ranges and other factors which vary by shape
• Diamonds meeting these requirements remain candidates for Excellent

Step 4: Light return grading

• As with color, clarity and finish grading, this assessment is performed by a trained gemologist
• This is not an assessment of fire or scintillation. It is an evaluation of fundamental light behavior, determining whether the diamond returns sufficient light, overall, to be considered top of class, or Excellent, for that shape
• Fancy shaped diamonds which successfully pass the first three steps and have Excellent light return will receive the overall cut grade of Excellent