Diamond Cut Grading System Based on 3D Model. A Strategy for Development

The words we use

We all agree that the Diamond Industry needs constant growth and development, but are some of the key marketing concepts we use still useful?

  • "A Diamond is Forever" does it lead to commoditization: "A Diamond is a Diamond"
  • We all say (including Labs) "the round brilliant is best"
  • "Ideal Cut" implies that everything else is less than "ideal"

The global consequences of using such concepts contribute to the commoditization of diamonds. If value adding decreases, there is an increasing risk of instability.
We would like to propose a way to develop a solution for the cut part of this problem by designing a system that gives equal rights of cut evaluation for all cuts. We believe this would be a useful tool that will lead to effective diversification. Our discussion will also consider grading systems used in other industries.

Three different cut grading approaches

  1. Parametrical
  2. Direct light measurements
  3. 3D diamond model

See also "Tree approaches to grade diamond cut: parametrical, direct light measurement, and 3D model".

Parametrical Approach

As shown in fig. 1 we believe all parametrical proportion based approaches could be considered as lying on a continuum beginning with a "few parameters" and progressing to "all parameters". We know that restricting consideration to only a few unrelated parameters (such as Table, Crown and Pavilion) is an improper method, but the consideration of all possible parameters and their inter-relationships is just not possible. This leads to the conclusion that parametrical approaches can not be successful in cut grading for round diamonds, let alone for fancy shapes.

Parametrical Approach

Figure 1. Parametrical Approach

Parametric systems have some uses in the planning of cutting, but are incapable of leading to the systematic development of new cuts.
The problems with the current parametrical approach in the field of symmetry grading are shown in the left hand side on the chart below. A solution to symmetry grading that we will propose and based on precise 3D diamond modeling is shown on the right hand side of this chart:

See also "How symmetry affects diamond appearance: mutual relationship between diamond proportions and symmetry".

Direct Light or Optical Measurements

Optical imaging or measurements may be produced by the means of equipment like Brilliancescope, Firescope, Hearts and Arrows Viewer, Idealscope, and Isse-2. However these grading systems suffer from poor perceptions of integrity because each system favors certain types of stones or the features of such stones. An example is shown in fig. 2. Some stones that look good or bad to our eyes may be graded differently by direct methods.

Figure 2. Stones like the one on left that shows very little leakage
will be favored by the Ideal-Scope, over the stone on the right
that shows more fire and scintillation.

The principle problems of the direct approach:

  • All structure lighting systems that rely on the human eye for interpretation will have different results depending on observer perception (in particular in different dynamic range and adaptation conditions);
  • Devices that measure light and evaluate a diamonds light responses attempt to give an objective result for the subjective way human eyes and the brain perceive diamonds;
  • We are unaware of current devices that can analyze a diamond through a range of tilting, or use many small (distant) light sources, to correctly estimate scintillation;
  • Optical methods can not be used effectively to develop new cuts;
  • All known approaches use a single view point. Humans have two eyes.

Proposed Three Dimensional Modeling Method

In order to explain this strategy we will firstly explain an important new concept called Basic Light Responses (BLR) and how Master Stones could be used to grade each of these BLR factors. With this understanding it is possible to show how an accurate 3D model of the diamond under consideration can be used by software systems to grade its cut quality.

a) Basic Light Responses (BLR)

Examples of Basic Light Responses (BLR):

  • Light return to the observer's eye;
  • Light leakage though the pavilion;
  • "Nail head";
  • ETAS - part of space visible trough moving diamond

A value for each BLR can be computed on the basis of a 3D mode.

The value is individual for each and every diamond and characterizes its cut.

Two types of such responses should be considered:

  1. Positive responses: e.g. scintillation, brilliance, fire, and contrast
  2. Negative responses: e.g. "fish-eye", "nail head", light leakage

From this information we wish to propose a new coefficient that is independent of lighting and viewing conditions; Effective Total Angular Size, or ETAS. This coefficient will be able to describe the optical potential of any polished and faceted diamond. ETAS will make it possible to predict the light responses from an individual diamond. The set of BLR coefficients will become redundant with respect to the set of visually observable properties. But in order to be able to relate ETAS properties to these observable features it is necessary to 'map the landscape' of both human and computer predictions of all BLR's and compare the computer predictions and calibrate them to the human responses. What follows is a proposal for a large scale master stone set study to perform this comparison.

b) Master stones for cut grading

The purpose of the Master Stones Set (MSS) is to:

  • Demonstrate appearance differences between diamonds of different grades
  • The "good diamond" or "bad diamond" concept will be applied to each positive and negative effect
  • There is no objective definition or formula for 'beauty'. It is necessary to accumulate and to analyze human perception data for each BLR.
  • Each Master Stone will be graded by different experts such as manufacturers, buyers and sellers. The experts will be chosen for their sensitivity to nuances of diamond appearance.
  • Human experience in judging diamonds and designing new cut styles is geographically dispersed. It is unlikely one organization can prepare this Master Stone set. The participation of various organizations to approve the set will prevent foolish errors.
  • Involvement of a complete range of manufacturing specialists and cut designers is most important when making such a set.
  • Manufacturers interested in developing, inventing and promoting new cut styles have the resources to add many new fancy shape stones to the MSS each year.
  • Properly graded new cuts will quickly populate new market niches. Naming protection can be provided by agreement from Labs, without the expense of patents and trademarks. Manufacturer's innovation and value adding will prevent diamonds becoming a commodity.
  • The Master Stone Set will include a variety of diamonds: good and bad, traditional and non-standard, round and fancy etc. As desirable and non-desirable effects become better understood, more innovation will lead to new cut styles and 'art proportions'.
  • The MSS will be used to verify or ratify ANY or ALL cut grading systems; all systems should give the same grades for stones that represent examples of specific good or bad BLR responses e.g. very good scintillation and very poor scintillation.
  • The organization that holds the MSS will make them available for institutions and laboratories involved in cut studies and grading.
  • Verification and validation of new grading systems will lead to greater consumer confidence and avoid contradictory grades.
  • New cuts may appear that lead to conflict of opinions of experts' or various grading systems. If grade variations are found to exist, then one or more systems may need revising.

c) Cluster approach to BLR data

The Master Stones Set will be divided into different BLR groups based on expert human grades; e.g. brilliance, scintillation, fire, and contrast. The same process will be performed by the computer based 3D model cut grades.

As a result we receive two sets of data that can then be compared: (1) Computation-based clusters and (2) Expertise-based clusters.
A proposed method for correlation between these two cluster maps is via 'Neural Networks', a special statistical method for comparing data arrays to build a common system.

The BLR-based grades and the experts' grades may match or not match:

  1. If they do match, then the system is complete.
  2. Clusters in the BLR grading match more than one cluster in the expert human observations; the match is not adequate.
  3. Clusters have inadequate matching.

To complete the cut grading system, we may need to improve either the computed BLR set, or question the expert observers.
In this way the Master Stone Set may be used to verify various cut grading systems and 3D models and the ETAS approach may be used for both Cut Grading and devising new cuts.

This approach is robust against errors in both diamond expertise and BLR computation.

Implementation: Lessons from Other Markets and Industries

It is useful to review grading systems for other goods and services such as wine, hotels and cars. Note that none use attributes like "ideal" or other terms such as perfect, because naturally there can only be one "ideal" item and so all other goods or services will be penalized. For individuals "ideals" exist, but different people have different ideals. The ideal concept conflicts with the concepts of "difference" and "specialty"; different or special are non-ideal or less than ideal and will be considered negatively. In the absence of the "ideality" concept, differences and specialties can be positive and increase the potential for growth and development.

Thus the concept of "Ideal" contradicts the concept of "consumer's preference" which is essentially what "differentiation" means, and differentiation is an important ingredient to grow and developing any market.

See "Examples of grading systems for different types of goods and services (wines, hotels, cars)".


We propose a cut grading system that fulfils the basic principles of evaluation of:

  • Equal rights for grading all cuts;
  • Equal rights for all proportions;
  • Similar stones get similar grades.

This grading system will match expert opinions on many phenomena of optical appearance that are known to contribute to diamond beauty, to a computer systems analysis of the diamond basic light responses (BLR).
For a description of a diamonds ability to scintillate, for example, a coefficient called Effective Total Angular Size (ETAS) can be introduced. This coefficient can be calculated on the base of a precise three dimensional model of the diamond under consideration.

The work to match the experts' and computer's opinions will be carried out using a Master Stone Set (MSS). This MSS will also become a verification standard for other cut grading organisations to ensure public confidence.

"A diamond is forever" has been an effective slogan for selling diamonds. But perhaps today it implies that any diamond will do?
Diamonds are eternal, AND beautiful, AND individual.
If diamonds loose their individuality, they become a commodity.
If diamonds are individual, every diamond is unique.

Labs have a responsibility to properly grade the diamond cut quality;

  • Grade ALL cuts on the same basis;
  • Stimulate new beautiful "fashion" cut development;
  • Return to "beauty" and "individuality";
  • More differentiation - less commoditization;
  • Consumers will prize creative cutters who achieves more beauty.


  • Sergey Sivovolenko, OctoNus, Moscow, Russia
  • Yuri Shelementiev, Gemological Center MSU, Moscow, Russia