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By  , Monday, August 06, 2007


For years Garry Holloway's diamond-cut consultancy has had strong alliances with leading international diamond researchers and websites.  Well-known for his portable ideal-scope, a tool used to show the cut quality of diamonds, he developed the Holloway Cut Adviser (HCA) system in 2000.  The HCA was used to grade the cut quality of more than a billion dollars of diamonds in its first year alone.

diamond-cut consultancy

Garry Holloway, FGAA, DipDT, JAA Appraiser


From Rapaport News (Jeff Miller) - The United States' Patent & Trademark Office issued patent No. 7,251,619 on July 31 to Garry Holloway of Canterbury, Australia, inventor of the HCA system, for a computer implemented method for evaluating a gemstone.

"The system and method are particularly suited for use in an online environment or may be utilized in conjunction with rough diamond analysis instruments in order to provide cutters with greater guidance as to the most appropriate dimensions to cut rough diamonds in order to maximize the yield of a rough diamond and to also produce a diamond of an acceptable grade," the patent's abstract read.

The original application was filed on June 18, 2001.


Full Description of the Patent

The present invention relates to the field of gem evaluation and more particularly to the field of diamond evaluation.

The cutting of gems such as diamonds is a highly skilled art with many variables that combine to create gems of varying qualities. The laws of physics dictate that, when proportioned correctly, a diamond will reflect back a maximum amount of the light that enters the stone. Because proportions are such a critical element in the diamond's beauty, the ideal cut has become identified as the standard of diamond beauty. In this regard the various parameters that define the cut of a diamond, including table, crown and pavilion angles, culet and girdle.

Most of a diamond's life and sparkle comes from its cut. Diamonds are often cut to retain weight, which results in light leaking out the back of the diamond, and also a dull drab diamond with a smaller diameter.

In 1919, Marcel Tolkowsky wrote a masters thesis on the ideal proportions for round diamonds. The proportions designated by Tolkowsky's have generally been considered as well chosen and have been the benchmark in the industry for the past 80 years. The target set by Tolkowsky was of a diamond with crown angle of 34.5 degree, pavilion 40.75 degree, and table of 53 percent.

However, Tolkowsky's ideal design has led to the industry developing the have been used to develop tolerances of an "ideal cut." This has been an incorrect application of Tolkowsky's ideal, as not all diamonds within the designated tolerances in fact could be described as "ideal." Further, recent research has shown that there are diamonds outside of the proportions indicated by Tolkowsky that are equally or even more beautiful.

Cut grading systems were developed in order to assist in classifying high quality cuts from lesser quality cuts. However, as existing cut grading systems are generally based on the developed tolerances, they are inadequate. Further such systems are feature oriented in that they provide a numerical grading for the diamond. Laboratories that provide such a numerical grading take the worst scoring feature and assign that score as a cut grade. This process ignores the complex interrelationship of facets as light reflects and refracts on its passage through a diamond. A diamond with a slight deviation on each of these measures can rate as ideal even though the performance is only fair. Equally some deviations for Tolkowsky's proportions can compensate for other undesirable deviations in other factors.

It is therefore apparent that large discrepancies can exist in the way institutional "tolerances" are applied to a single "ideal cut." Further, today's grading systems are not flexible enough to take account of different proportion preferences of individuals or geographic markets. Many consumers, particularly sophisticated consumers, expect more of cut grading systems. There is therefore a need for a more flexible and accurate grading system.

It is also apparent that there are many variables in assessing the quality and beauty of a diamond, and that, particularly from the lay person's point of view, it can be a difficult decision choosing the right diamond. There is therefore a need for a simplified gem assessment system and method.

In addition, there are numerous diamond traders around the world selling diamonds of varying quality. For a person, particularly one not experienced in the gem trade, it can be a difficult process evaluating diamonds and judging their appearance based upon the cut factors listed by the traders. Also, it can be time-consuming process evaluating diamonds from the various traders.

There is therefore also a need for an improved system for evaluating gems of multiple remote traders.

The present invention seeks to overcome or alleviate at least one of the problems of the prior art.


According to a first aspect of the present invention, a system has been developed whereby the various cuts of a diamond are defined in terms of individual user preferences. That is, the various cuts of a diamond are assessed according to factors that characterize the beauty and desirability of the diamond.

In this regard, three factors are commonly used to assess the beauty of a diamond being brilliance, fire or dispersion and scintillation.

Brilliance: Brilliance is generally considered to be the most important feature when considering diamond beauty. If brilliance is compromised then the effectiveness of a diamond's fire and scintillation is also reduced. Brilliance is often related to proportions that reduce light loss from the pavilion of a diamond. The understanding of brilliance must include the directions in which light travels to an observer and the source and type of light used in any analysis.

Fire or Dispersion: Fire is the term used to describe the spectral separation or dispersion of white light into rainbow flashes. Fire is generally considered to be enhanced with steeper crown angles and smaller tables.

Scintillation: Scintillation is perhaps the least clearly defined visual feature in diamond appearance. One definition is "a pleasing visual balance in the spread of clearly defined and well spread dark and light areas that flash on and off as a light source, the stone or the observer's position change". The dark areas should be a small component of the overall stone's face up appearance with a head shadow of 21 degrees. Scintillation is dependent on the type of lighting, the observer's physical presence and the diamond itself. It is more personal than brilliance and fire, because the more of these two features the better, whereas the ideal amount of blackness and contrast is in the eye of the beholder.

Spread: A further desirability factor that may be considered in the system according to the present invention is "diameter spread." That diamonds of the same weight but different proportions can appear bigger or smaller is often referred to as "spread." This factor, however, is an economic or desirability factor rather than a beauty factor.

According to a first embodiment of the invention, the system is fed various cut features of a diamond, such as crown and pavilion angles and table percentage. Based upon the actual values, input, the system produces a simple description of the visual appearance of the diamond in terms of the beauty factors of the diamond. Therefore, in this way, rather than just providing a numeric grade, the customer is provided with a definition from which the individual is able to form their own opinion, based upon personal or regional taste.

In this regard, the present invention uses a look-up table or the like which matches diamonds having particular cut features with appropriate beauty factors.

In this regard, according to the first embodiment of the invention, weightings are given to all of the factors being considered. Fromweightings it is apparent that the system is based upon holistic information, rather than unrelated individual features, and that the feature considered most important in assessing diamond beauty is brilliance.

In order to apply the holistic information to particular diamond cuts, a cross correlation between the various cuts and the holistic information needs to be established. This may be achieved in various ways, such as by studying actual diamonds in order to calculate penalty values. However, it is more efficiently performed using virtual diamond analysis, as this eliminates problems with variation in color, clarity and the minor facet groups. Examples of software programs that may be utilized include Diamcalc, Firescope, and Gilbertson-Scope. These software packages are available from OctoNus Software Limited, a company founded by Moscow State University, Russia.

Such software programs may be used to develop charts of diamond images of the most commonly encountered diamond proportions. For the present example, the range chosen was for table sizes between 54 percentand 65 percent on a grid of the pavilion angles between 39.5 degree and 43 degree in 0.5 degree graduations and steps of one degree for crown angles between 28 degree and 40 degree/diamonds_info

The Firescope instrument, as distinct from the Firescope software, enables the light return of real diamonds to be studied and appropriate weightings given in regard to brilliance. In this regard, using the virtual Firescope software, it has been found that consumers show a preference for diamonds with a strong red light return and a black eight star pattern. Therefore, using the Firescope software, diamonds displaying this feature were given a good brilliance rating.

From this analysis it became apparent that as table size increases, the black stars in the stones identified as falling within the recommended areas are seen to become thinner and less well defined. Also, it became apparent that variations in pavilion angles could be compensated for by a larger opposing variation in crown angles. This resulted in a broader range of proportions than the Tolkowsky proportions that yielded beautiful diamonds.

Therefore, such subjective analysis was applied to all the virtual diamonds in the grid patterns using the Diamcalc software tools, predominantly from a "face up" position, and each given an appropriate brilliance score of zero to four, whereby the lower the score, the better the brilliance.

In order to verify the results, cross correlation was performed by comparing diamonds with the same score from different areas on each grid, and those from other table size grids. Finally results were confirmed by showing actual diamonds with known proportions to numerous observers in various lighting environments.

It is to be appreciated that the results were produced essentially by considering the face up viewing position of the diamond because of the economic importance of this position. This is because most diamond sales are made by observing diamonds from a face up view. Nevertheless, this is not an essential component of the invention, and the model used in developing weightings could equally be based upon other viewing positions, such as oblique positions.

Although the aesthetic penalties in relation to brilliance, fire, scintillation and diameter spread are the most preferred qualities to account for, penalties or adjustments in relation to other aesthetic qualities may also be taken into account in the overall model.

Vertical Spread Adjustment

For example, in another embodiment of the invention, a further aesthetic feature of diamonds that may be taken into consideration in calculating a penalty weighting is vertical spread. Vertical spread is different to diameter spread. It is an issue that consumers raise from time to time and is the amount of diamond that can be seen projecting above a setting. Generally vertical spread comes at the cost of reducing "diameter spread." For example, a somewhat subjective allowance for this factor could be a 20 percent weighing in the spread factor for stones with steep crowns and small tables.

Table Size Adjustments

Generally, the best looking diamonds have table sizes of 53 percent to 60 percent (measured as a percentage of the diameter of the diamond.) Diamonds with table sizes that are too large or too small have some impact on diamond beauty. Hence, it is preferable for a penalty factor for such table sizes to be applied to each of the beauty factors.

Hence, a diamond with a table size of 62.5 percent has scores of brilliance of 0.5, fire 0.643 and scintillation 0.643 giving a total penalty of 1.786. This means it is possible for a diamond with this size table to score an excellent grade.

Girdle Adjustment

In a still further embodiment of the invention, a further aesthetic feature that may be taken into consideration in calculating penalty weightings is an adjustment for the girdle thickness. Ray path analysis shows that polished girdles refract some light back above the girdle in the same way as other facets. However, for this to occur, it would require a diamond to be set with an exposed girdle. Nevertheless, on balance, thick girdles result in less light return and can look like inclusions, especially if bruted rather than faceted. Thick, very thick and extremely thick girdles weigh much more but are one of the most effective ways to maintain yield without sacrificing beauty. Diamonds with extremely thin and very thin girdles are given a penalty because of the undesirable risk of damage. It should be noted that the spread factor provides an additional penalty for a diamond with an overly thick girdle.

With these considerations in mind there would bea penalty deduction for overly thin and overly thick girdles. Hence in the girdle range between 4 percent and 10 percent, the penalty is between zero to one on a continuum, and the continuum extends further for excessively large girdles.

Fish Eye Adjustment

According to a further embodiment of the invention, an adjustment may be made for fish-eyes. A fish-eye appears as a circular inclusion and is a reflection of the girdle on the opposite side. Fish eyes are most apparent if the pavilion is shallow and the table is large or a combination of the two. Fish eyes can be seen in diamonds with a 41 degree pavilion and 72.2 percent table and at 390 pavilion and 58.4 percenttable and any proportions in between, with no tilt. Also, as the table gets 1 percent bigger, a 1 percent larger fish-eye is apparent. Nevertheless, a near fish-eye may be considered desirable because the stone will have an excellent spread.

In relation to the weightings given to diamonds evaluated using the present invention, a score of 1 is added for 0 percent on a sliding scale where 5 percent is given 0.2.

As fish-eyes are generally an undesirable trait, an automated comment in relation to the fish-eye should be generated for appropriate stones. If <1% or less do not buy this diamond under any circumstances, as it is a fisheye, and >1% to <3% this diamond is almost a fisheye, and >3% to 5% a small amount of tilt will show a fisheye under the table of this diamond.

The percentages in this table refer to the ABC Page-Thiesen Diamond Grading scheme, although any suitable grading system may be utilized.

Culet Adjustment

A large culet on a diamond allows a small amount of light loss, but more importantly mars the appearance. In this regard, a culet often appears as a black inclusion.

In order to account for this problem, if a culet size is smaller than 1 percent, no penalty is added. However, for culet sizes above 1 percent a penalty is added on a sliding scale, with a 5 percent culet size adding a penalty of 0.8.

Advisory System

With all required weightings and adjustments determined, these calculations may then be utilized in a user-friendly system for evaluating a diamond. In this regard, the system would operate by requiring a user to directly input the cut parameters of a diamond of interest, or via an interface with a proportion measuring device or other proportion data processing means.

Based upon the input parameters, the system will then match these parameters with the relevant tables of brilliance, fire, scintillation and spread ratings and other applicable adjustments in order to obtain an appropriate weighting for each factor, as well as a total score. An overall comment may also be provided.

For example, for a diamond having a table of 56 percent, a pavilion angle of 42 degree, a crown angle of 31 degree, a girdle of 2 percent and a culet of 0 percent, the diamond will obtain a weighting of 1.0 for brilliance, 1.0 for fire, 1.0 for scintillation and about 0.46 for spread. This diamond will therefore have an overall penalty of 3.46. It is to be appreciated that the worst looking diamond would be rated as ten or more. A score of zero would be extremely uncommon, and in fact most popular Tolkowsky proportioned diamonds would score around one. It is hence apparent that this penalty is based upon aesthetic principles and is therefore likely to have more meaning to a lay person.

In addition to the numeric aesthetic penalty rating, it is possible to provide the user with a descriptive assessment of the diamond based upon the diamond cut parameters and/or the penalty weightings given for the aesthetic parameters of brilliance, fire, scintillation and spread. Therefore, in simple words the system can describe how each diamond will most likely look to a buyer in a jewelry store lighting environment for each of the above parameters.

For example, it is possible for the advisory system to recognize three distinct types of diamond with optimum beauty, being Tolkowsky's Ideal Cut (TIC), Brilliant Ideal Cuts (BIC) and Fiery Ideal Cuts (FIC). Brilliant Ideal Cuts return the most light and tend to have the largest spread for the same weight. Fiery Ideal Cuts have more fire or spectral color and appear to have more facets and scintillation. An FIC is a cut with a steep crown angle in order to increase fire or dispersion, while having a slight reduction in pavilion angle to maintain optimum dispersion. A BIC on the other hand is one with a shallower crown angle and slightly deeper pavilion in order to optimize brilliance. The TIC range combines a balance of fire and brilliance. BIC diamonds tend to weigh less and FIC diamonds weigh more for the same diameter spread.

Therefore, when one of these stones is recognized, the system can include a statement in the assessment, such as:

"This stone exhibits characteristics of a TIC/BIC/FIC."

In this regard, BIC, TIC and FIC characteristics are only given for diamonds in the excellent range (i.e. less than 2) and with the following crown angles: Crown Angle Diamond Type less than 32.5 degree, BIC more than 35.5 degree, FIC between 32.5 degree, and 35.5 degree TIC.

The system can also provide an assessment based upon each feature being assessed. For example:

Brilliance: 0 This diamond has ideal brilliance; 1 This diamond has very good brilliance; 2 This diamond has good brilliance; 3 This diamond has fair brilliance; 4 This diamond has poor brilliance

Fire or Dispersion 0 is very firey 1 has good fire.

Scintillation 0 and has excellent scintillation 1 and has good scintillation 2 and has poor scintillation.

Spread 0 It has a very good "spread" or large diameter for its weight 1 It has a reasonable diameter or "spread" for its weight 2 It is deeply cut and has a poor "spread" or diameter for its weight.

Symmetry; 0 The symmetry is excellent; 0.5 The symmetry is good; 1 The symmetry is poor.

Polish; 0 and the polish is excellent; 0.5 and the polish is good; 1 and the polish is poor

Girdle Thickness; 0 with a medium girdle (very good) 0.5 with a very thin girdle (can chip); 0.5 with a thicker than ideal girdle, so it weights about x % more than if it had a thinner girdle 0.5 this diamond has an extremely thin girdle that is prone to chipping, but the spread is bigger than you would expect 1 this diamond will lose some brilliance through its extremely thick girdle, it weighs about xx% more than it should

The present invention therefore provides a system able to furnish a description of the visual appearance of diamonds in simple terms, even though the variables and issues involved are enormously complex. That is, the present invention is able to turn the numerical cut grades into a benefit based rating that defines the cut of a diamond in ways that individual preferences can be identified and satisfied.

In particular the system aids both novice consumers and experienced buyers in selecting unseen diamonds, as if each diamond were lined up side by side.

In fact, in a further embodiment of the invention, where the present advisory system is provided over the Internet, a database could be formed by having a number of traders upload proportions of their diamonds that are for sale. The proportions would preferably be determined using proportion measuring devices, such as those manufactured by Sarin Technologies and Ogi Corporation. For example, Sarin Technologies market a desk-top measurement device that takes a series of 64 pictures of a rotating diamond and measure all its angles and proportions digitally.

Potential customers could then obtain reports using the advisory system in relation to these diamonds, based upon the proportion information, and also view virtual models of the diamonds, created from the proportion information by using virtual modeling tools, like Diamcalc.

In a further embodiment of the invention, proportion measuring devices are used to model every facet of a diamond making it then possible to account for symmetry and other faceting variations and defects, which are then able to be included in the advisory system. This would then enable a virtual image to be generated. Alternatively, the image displayed to the user may be a digital photograph of the appropriate diamond.

Therefore, in addition to the user being given an aesthetic grading and appropriate comment on the diamond, an equivalent image of the diamond may be displayed before the user together with details relating to the relevant trader, such as a hot-link to the trader's site.

The present invention may also be advantageously used in overcoming the problems in existing grading systems, which include inadequate cuts within the "top grades" and exclude other diamonds with favorable combinations of rejected proportions. Thus, current systems unfortunately lead cutters to cut for grades and attract healthy margins, as compared to cutting for beauty. That is, diamond cutters will generally cut a diamond within the recognized tolerances of an "ideal cut" which weighs the most, but which typically is dull and drab, as they make more money by cutting deeper, heavier diamonds that leave a little more weight on the crown and pavilion, even though in actuality, these are not the more beautiful diamonds.

The present invention, however, may be used to redress this problem, in that the cut advisory system may be programmed into rough diamond analysis instruments. This will provide cutters with greater guidance as to the most appropriate dimensions to cut rough diamonds in order to maximize the yield of a rough diamond and to also produce a diamond of an acceptable grade.

Variations and additions are possible within the general inventive concept as will be apparent to those skilled in the art.


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