Diamond Cuts

Diamond Cut Basics

What is diamond cut?

Cut refers to the proportions and relative angles of a faceted diamond. A diamond's cut should not be confused with its shape. Cut is a quality factor that determines value along with the other 4Cs of Carat Weight, Diamond Clarity, and Diamond Color.

Ideal Cut Round Diamond
Posted by jcrow
2.13 J SI2 Ideal Cut Diamond

*Note - This tutorial discusses cut quality of round brilliant diamonds. For more information about Fancy Shapes, please visit: Fancy Diamond Shape Tutorial

How important is diamond cut?

Out of the 4Cs, diamond cut has the biggest impact on sparkle, brilliance and fire. A diamond's cut quality is a fine balance of proportions and angles, and most diamonds in the marketplace are average cuts. A well-cut diamond will sparkle more and will be livelier than a diamond that is poorly cut. When you are evaluating the 4Cs, understand that Cut trumps the others by turning a pebble of a diamond into a sparkling gem.

Diamond Anatomy and Proportions

To understand diamond cut, the first step is learning the parts of a diamond. Please visit: Anatomy of a Round Brilliant Diamond for the basic facet structure. The image below shows essential proportions of diamond cut.

Diamond Proportions

Ideal Cut Round Diamond

Proportions and Light Return

The Ideal-Scope reference chart below illustrates the effect of proportions on light return. Well-cut stones show maximum brilliance while shallow or deep stones have zones where light escapes and is not returned to the viewer's eye. To learn more about using this diamond tool, please visit: Ideal-Scope Guide

Ideal-Scope Reference Chart

Ideal-Scope reference chart for diamond proportions
©2003 Ideal-Scope

Diamond Cut - The Nitty Gritty

Do different labs have different cut grades?

Well known labs with definitive cut grades for round diamonds are GIA, AGSL, IGI, EGL, and HRD. For more information on these laboratory cut grades please visit:

GIA Diamond Cut Grading System

AGS Laboratories Cut Grading System

IGI Diamond Reports


HRD Antwerp

*Note - AGS Labs has developed the first diamond cut grade for princess cut diamonds, and cut grades are offered on oval cut and emerald cut diamonds. For more information on the AGS Lab fancy shape diamond cut grades please visit: AGS Light Performance Cut Grade

How is diamond cut graded?

     Three Approaches to Cut Grading:

1. Proportions are measured with a Sarin, Ogi, or Helium scanner. Old systems use the worst proportion as the 'grade maker'. AGS used this flawed method until May 2005.

You can reject bad proportioned diamonds with Pricescope's free HCA for round diamonds and AGA for other shapes. These tools can narrow your search, but are not for final selection. Symmetry and other factors also need to be considered.

Helium Scanner

2. Direct assessmentIdeal-Scope viewers and photos show leakage and light return. Hearts and Arrows viewers are for grading symmetry, but some H&A's do not score <2 on HCA. Optical symmetry does not always equal the best light return.

The Brilliancescope and ISee-2 shine light onto a diamond and give digital pixel counts. Both give a good indication of diamond performance, but neither gives the same grade for the same diamond.

Ideal-Scope Pattern Features

3. A virtual 3D model from a Sarin or Helium scanner can be viewed and tested with a free GemAdviser download. 3D methods give new R&D Ray Trace Cut info and virtual ideal-scope images.
Diamond Calculator

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