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Another GIA press release on diamond cut research

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Serg

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"Editor’s Note:

Every Facet Really Does Matter to the Appearance of a Round Brilliant Cut Diamond—Revisited
Based on correspondence received following the original publication of this article in the Feb. 13th edition of the GIA Insider, the authors have decided to clarify certain aspects of their description, and offer a revised version.


[Back to Top] [Print Article]


February 27, 2004"

GIA changed angles in Table1,Star length, Changed index for lower facets too, but save photo.

Some statements became more correct but more misleading for consumers in same time.


Below New Table1
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Proportion
Commercial cut
Hearts On Fire
Fabrikant Brilliant

Crown angle
34.5°
34.0°
34.0°

Pavilion angle
41.0°
40.8°
41.2°

Table percentage
56%
54%
56%

Girdle thickness
4.3%
3.0%
4.0%

Total depth
62.5%
61.6%
62.3%

Star length
60%
55%
60%

Lower girdle length
80%
80%
80%

Average amount of indexing
3.5° (“painted” facets)

– 4.0° (“dug out” facets)
 

Iiro

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Tho whole article is rewritten!

A new pic of a tang and new facets to diamonds in the drawing.

Dig out and painted facets

This is good sign, GIA showed they are able to hear, but it is uncertain who they listened
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( correspondance with whom?)
 

Iiro

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Now I have read the new article.

Looks like they have rerun the stones in SARIN. What else can explain the new specs in TABLE 1 ?



Also, why they dont understand the weight issue?

I have seen diamonds with painted upper girdle facets, and they have been the lightest diamonds so far. The painted facets ALLOW to make thinner girdle, the dug out DONT allow.

Cutter can make a thick girdle to ANY combination of dug out or painted facets, but he can make thinner APPEARANCE with dug out facets and retain more total weight with same diameter.

What was the weight of these three stones? The size can alter the looks of the diamond in their lighting environment.

Tolkowsky did not take the size seriously.

His stones were like this:
The stones are not in actual size. The biggest one has diameter of 21.07 mm
Tolkowskyn%20kivet%20kuvassa.jpg


Is it the same with GIA?

If someone disagrees with the size differencies of the Tolkowsky 5 stone series, please inform or correct
1.gif
The picture is a part of my thread in a Finnish language forum for diamonds.
 

Garry H (Cut Nut)

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It would be appropriate for someone from EightStar Diamonds to comment on this topic, since in effect the GIA has indicated that the process 8* use results in a worse looking diamond.

I want to make it clear that I do not agree with GIA except in instances where diamonds are very shallow. But in such a case the shallowness is a result of flat rough and there is usually not enough material to make a thicker girdle at the mains without getting an extremely thin girdle at and near the minor / half facet junction.

People who want to understand the issues can see the pictures at the bottom of this page http://www.gemology.ru/cut/english/symmetry/6.htm http://www.gemology.ru/cut/english/symmetry/6.htm
I hope I put the link in correctly.
Here is the text from there just in case.
(and BTW it was noted that the revision changed the offending comment that no-one had published anything about this topic before. But the revision did not mention that we had published this both on the website listed above and in the Russian Gem Center's journal which is exchanged with G&G. And that is not to mention that there have been many discussions of indexing both here and at DT.)

Example 3. Girdle thickness continuity. The girdle of a round brilliant cut diamond normally has 16 thinner and 16 thicker regions. All the thinner regions are of the same type, while the thicker ones can be divided into two types: main facet junctions and edge (or minor) facet junctions. The girdle thickness may differ from one type to the other. In the example shown in Fig. 5, the girdle is thicker at the main facet junctions than at the edge junctions. This occurs when the upper and lower girdle facets are slightly tilted with respect to the diamond axis (azimuth angle deviation). Since many laboratories (especially in America) measure girdles at their thinner regions, their cut grades are not affected by the increase in the girdle thickness at this thicker region. This fact can be used to increase the actual thickness of the girdle, without affecting the reported thickness, and therefore to increase the stone weight by 2-3%. Unfortunately this trick negatively affects the optical properties of the diamond because it increases the steepness of the upper girdle facets. (Changing the azimuth of the upper girdle facets in the opposite way may improve the optical properties of the stone. This idea is used, for example, by EightStar Diamonds®).





Fig. 5. The girdle of this diamond is perfectly made in the thinner regions in order to allow it to be graded as AGS 0. However, the thickness of the thicker regions of the girdle has been increased in order to increase the weight yield of the stone. The 46.2° tilt angle of twin upper girdle facets compensates for the thickened girdle and compares unfavorably with a similar proportioned normal girdle stone with a tilt angle of twin upper girdle facets of 41.3°.

Fig. 6 illustrates real examples of two diamonds with the girdle shape described above.




We could give more examples, but our goal is not to create a list, it is to demonstrate the breadth of the problem. The problem is that in some cases stones that look good are graded poorly, because they lack symmetry according to the chosen symmetry grading system. On the other hand, some stones look bad and their actual symmetry is poor, when the current symmetry grading systems report that they are good.
 

Garry H (Cut Nut)

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The pavilion angles on these diamonds are very close to the same.

The crown angle on the leaky cheated girdle stone (at the bottom) averages 33.3 and the upper girdles are mostly around 46 degrees. It has also a larger table (from looking not measuring).

The 8* (upper DiamCalc) has average crown angles of 34.8 and 37 for the upper halfs.

So you can see why there is less leakage in the 8*.

Now I agree that some leakage can be good at the girdle and provides contrast.

This is explained in one of our newsletters at http://www.ideal-scope.com/newsletter_issue_003.asp

(Btw please subscribe for the newsletters because we give your names and email addresses to african people who will give you millions of dollars for free)

Eightstar on top and cheated on bottom.JPG
 

Colored Gemstone Nut

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Interesting Garry...
21.gif
 

EightStar

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Life has become a much more stimulating proposition now that we have the information superhighway the Internet has become. Information is traded at a much higher rate now than the pre-baud days of newsperiodicals arriving in the mail or being purchased at a bookshop. Forums such as this one serve as a perfect example to underscore my point.

There is, however, a price to pay occasionally for the access to information we all now have right on the other side of our computer screens. I am referring to, of course, MIS-information. I find among the recent posts here one that is misleading due to its basis outside actual fact. I refer specifically to these words:

"It would be appropriate for someone from EightStar Diamonds to comment on this topic, since in effect the GIA has indicated that the process 8* use results in a worse looking diamond."

What the GIA has written, prompting the above quote, is about digging and painting facets on diamonds and how this practice yields a "different" look. Nowhere is it implied that "different" and "worse" are – or ever should be – used synonymously. In the article the GIA refers specifically to crown facets. They are NOT speaking about EightStar diamonds directly or by implication.

EightStar diamonds began 20 years ago flying in the face of convention since we found that convention to be based on weight-saving techniques, time-saving techniques, and a mathematical model that was naïve. Cutting techniques before EightStar were utilized in a form analogous to hunting with bows and arrows and sling-shots. EightStar raised the bar to a level that can be equated in the analogy to hunting with a rifle equipped with a laser sight. Analysis of diamonds prior to our revolutionary cut was, and continues to be to this day, inadequate to measure the subtleties of minutiae in facet alignment and of something much more important: the symbiosis of crown and pavilion required to achieve the brilliance we are known for. Our breakthrough was of enormous proportions and has inspired a whole host of radical gyrations in our industry which includes:

a. Hundreds of imitators of EightStar in the guise of "hearts and arrows" diamonds
b. A plethora of brand names

It is not possible to have engendered such a monumental change in the practices of diamond polishing without doing something "different". The difference we have made cannot be measured by technology such as Sarin® and there can be no accurate formulamatic scales into which one "plugs" Sarin readings of diamonds to determine whether the cut is superior or inferior to any other except in a very rudimentary way.

As a result of research we began in 1990 in America with EightStar diamonds, we have passed along terms to our profession that are telling about the infrastructure of our modus operandi: Optical Symmetry, Edge-to-edge Brilliance, Firescope View, Three-dimensional Symmetry, Reflected-image Technology, the Performance of a Diamond, as well as many other terms we coined.

The "look" we have created was intended to be different because we found what existed before us to be unacceptable once we understood the symbiotic nature of the relationship between path-of-light mirror alignment and the two-headed phenomena of brilliance and fire. It is our feeling that one of our greatest contributions to diamonds to date was the unprecedented increases we made in brilliance and fire.

After growing up in a family of middle class automobiles and coming to accept the mushy, boat-like ride of the dinosaur cars of the 50’s and 60’s to be the norm, I found my first ride in an expensive European car to be disorienting. I mistook the sold ride and positive steering to be only a rough equivalent of what I was used to since I was doing what most of us do: judging the outcome of a revolution using the unevolved metering tools of what came before it.

So, to set the record straight, the GIA has NOT said or implied that EightStar diamonds are inferior in their appearance. EightStar diamonds do have a different appearance due to our cutting methods that require far more time and yield greater weight loss. Different is a good thing for us. We do what we do deliberately and with our eyes fully open.

Richard von Sternberg
Owner, EightStar Diamond Company
 

Serg

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Hi, Richard

Did you read the first redaction of GIA article? :"the stone on the left in figure B demonstrates, some approaches to cutting the upper and lower girdle facets produce a less pleasing appearance from essentially the same proportions."

"
I think You mean only second redaction:"The round brilliant on the left is a commercial diamond in which the upper and lower girdle facets have been displaced toward the bezels and pavilion mains (as in figure B, left). This diamond shows little contrast except for the dark appearance of the pavilion mains beneath the table. "

I think you miss one point:



"The girdle of a round brilliant cut diamond normally has 16 thinner and 16 thicker regions. All the thinner regions are of the same type, while the thicker ones can be divided into two types: main facet junctions and edge (or minor) facet junctions. The girdle thickness may differ from one type to the other. In the example shown in Fig. 5, the girdle is thicker at the main facet junctions than at the edge junctions. This occurs when the upper and lower girdle facets are slightly tilted with respect to the diamond axis (azimuth angle deviation). Since many laboratories (especially in America) measure girdles at their thinner regions, their cut grades are not affected by the increase in the girdle thickness at this thicker region. This fact can be used to increase the actual thickness of the girdle, without affecting the reported thickness, and therefore to increase the stone weight by 2-3%. Unfortunately this trick negatively affects the optical properties of the diamond because it increases the steepness of the upper girdle facets. (Changing the azimuth of the upper girdle facets in the opposite way may improve the optical properties of the stone. This idea is used, for example, by EightStar Diamonds®)."

http://www.cutstudy.com/cut/english/symmetry/6.htm

© 2003 S.B. Sivovolenko, Yu.B. Shelementyev, Garry Holloway
 

EightStar

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Serge,

It has always been my practice to restrict my postings on internet forums to those things which would not compromise any trade secrets we protect or lead people to understand better what we do and why. Looking at what you have said about us brings me to this issue once again. I have decided not to go into detail about what you have said about how we fashion diamonds. I will only say that, considering your glowing qualifications and background, you are surprisingly wrong.

Richard von Sternberg
 

Rhino

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Greetings from the east Richard!
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Serg, Gary ... do you understand why Richard says you are wrong?




What intrigues me from this article is how you (Serg, Gary) think that the EightStar tweaking of the upper girdles negatively impacts the optical properties of the diamond. Haven't you guys traditionallly viewed this as a positive effect? Curious.
 

Serg

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Richard,

If I made mistake it is not problem. Anyone can correct my statement. Try.

FYI It is not a problem any more received precise 3D of any round stones.( I do not speak about Sarin) Please think about it
 

Serg

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----------------
On 3/1/2004 3:47:21 PM Rhino wrote:


Greetings from the east Richard!
1.gif



Serg, Gary ... do you understand why Richard says you are wrong?


What intrigues me from this article is how you (Serg, Gary) think that the EightStar tweaking of the upper girdles negatively impacts the optical properties of the diamond. Haven't you guys traditionallly viewed this as a positive effect? Curious.
----------------


Rhino,

I think you and Richard miss something.

Where did we talk "that the EightStar tweaking of the upper girdles negatively impacts the optical properties of the diamond" ?
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Rhino

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----------------
On 3/1/2004 2:36:39 PM Serg wrote:





Unfortunately this trick negatively affects the optical properties of the diamond because it increases the steepness of the upper girdle facets. (Changing the azimuth of the upper girdle facets in the opposite way may improve the optical properties of the stone. This idea is used, for example, by EightStar Diamonds®).'

http://www.cutstudy.com/cut/english/symmetry/6.htm

© 2003 S.B. Sivovolenko, Yu.B. Shelementyev, Garry Holloway

----------------
Peace,
 

pricescope

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----------------
Unfortunately this trick negatively affects the optical properties of the diamond because it increases the steepness of the upper girdle facets. (Changing the azimuth of the upper girdle facets in the opposite way may improve the optical properties of the stone. This idea is used, for example, by EightStar Diamonds®.'

http://www.cutstudy.com/cut/english/symmetry/6.htm

© 2003 S.B. Sivovolenko, Yu.B. Shelementyev, Garry Holloway
----------------
 

Garry H (Cut Nut)

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Richard you seem to take anything I ever mention as a criticism.
This is wrong. I merely invited you to comment on the remarks that the GIA rsearchers have made, with which I disagree, that denigrate one technique you use to produce a very nice product that I have never denigrated publicly or privately.

However you say your stones have more "brilliance". Since no one has a way to measure brilliance yet, we chould perhaps qualify your statement : 8* diamonds produce very high light return, especially at the edges.

Have you read the newsletters at www.ideal-scope.com on the topic of the benefit of the role that leakage can provide in additional contrast. Contrast plays a role, with light return, in brilliance.
 

Rhino

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My bad ... at first glance it almost appeared to say that "the negative effect" was something 8* was doing.
 

strmrdr

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I just wanted to say that untill this thread desended into name calling and bruised ego's I was learning a lot from it.

*strmrdr goes back to his desk*

Can we get back on track I would like to learn some more neat stuff.
Thank you for sharing with us and hopefully we will see more of the deep technical stuff here.

EightStar welcome to pricescope and I hope you will hang around and share with us under better conditions.
 

Serg

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----------------
On 3/1/2004 3:47:21 PM Rhino wrote:




Serg, Gary ... do you understand why Richard says you are wrong?


----------------

Rhino,
1) Perhaps, he means, that only the upper crown facets are rotated at the stones *8, whereas GIA wrote: "the upper and lower girdle facets have been displaced toward the bezels and pavilion mains". Taking into account this fact, ctititisism of GIA article is not corrected with the help of example of stones *8 (nobody from us doesn't criticize stones *8 in this topic), because rotation of lower girdle facets greatly influences at stone's beauty (on the assumption of lower girdle facets were really rotated).
Prima facie rotation of lower girdle facets on 3-4 degrees should destroy the all stone's pattern and it is unlikely that anyone would spoil a stone.

At our article we described only rotation of upper crown facets. Really I didn't see the diamond models where lower crown facets are rotated. Can somebody publishes Sarin 3D model of such stone, where both types of girdle facets are rotated? For example, model of Fabricant Brilliant? I would like to make sure that not only upper girdle facets, but lower girdle facets are rotated on the same angle at this cut.

2) Also, possible, Richard means upper crown facets are rotated at the stones *8 more , than at the GIA article.
 

Garry H (Cut Nut)

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For reference purpose I am linking this discussion to some charts that Bruce Harding produced that explain the change of angles that result from changes to angle of azimuth.
https://www.pricescope.com/community/threads/twist-break-facets-crown.14385/

Thanks Bruce.
This will be of value one day i am sure.
Note that the lower girdle facets can also be indexed.
I wonder if anyone can produce a gemCad of 1 degree each side of normal so we can model it in DiamCalc ?
email it if you can please and I will post DiamCalc's here.

[email protected]
 

valeria101

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Date: 11/27/2004 7:54:20 PM
Author: Garry H (Cut Nut)
bump
For the benefit of some of those reading anbout Yaw and indexing.
Sure. Thanks !
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Garry H (Cut Nut)

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I was just trying to find the GIA article about painting and dug out facets - it has never been added to their articles on cut in the website so i thought I would paste the text here.
Already they made some changes to it since they first put it up - they initially implied the GIA team had ''discovered'' this idea - which is rubbish since we have been discussing it here for many years. In personal communication we were told that this venue is not ''published'' so we pointed to the symmetry article that Sergey, Yuri and I wrote that was published in the Russian Gem Center Journal that GIA gets. They apologised, but rather than change the text to add that - they changed the text completely.
So since most of what is written here is rubbish - I thought I would make sure it remains on the public record.

BTW - we should use Painted and Dug Out as the standard terminology - that way we do not get too many words that mena the same thing

February 13, 2004

From Gems & Gemology: Every Facet Really Does Matter to the Appearance of a Round Brilliant Cut Diamond—Revisited



Based on correspondence received following the original publication of this article in the Feb. 13 edition of the GIA Insider, the authors decided to clarify certain aspects of their description, and offer the following revised version.

In the course of GIA’s research into the effect of proportions on the appearance of a round brilliant cut diamond, we have looked at many aspects of this cutting style, including a number of diamonds with cuts that have interesting variations from what is considered standard. The round brilliant is typically described by its proportions and angles: total depth percentage, crown height percentage, pavilion depth percentage, table percentage, average crown angle, and average pavilion angle (along with girdle size and condition, culet size, and finish quality). In our article in the Fall 2001 issue of Gems & Gemology, we pointed out the significance of two other parameters – the lengths of the lower girdle and star facets (the latter determines the length of the upper girdle facets as well). These parameters define the positions and areas of the star, upper girdle, and lower girdle facets, which typically cover more than half the surface area of a round brilliant. The importance of these facets, which was noted briefly by Marcel Tolkowsky in his 1919 treatise on cut, is again being recognized after decades of omission from proportion-based diamond cut grading systems.


However, the above description does not include another important aspect of a diamond’s shape: the orientation of the upper and lower girdle facets (sometimes referred to as “half” facets). In a standard round brilliant diamond, these facets are evenly spaced around the diamond. Yet upper and lower girdle facets can also be polished so that they lean toward the bezel or pavilion main facets and away from each other (facets created in this manner are referred to by diamond cutters as “painted” facets). This change in orientation reduces the angle to the horizontal of the upper and lower girdle facets, and yields a shallower angle between the half facets and the adjacent bezels and pavilion mains. Alternatively, the half facets can be fashioned so that they lean toward each other, thereby creating steeper angles between each upper or lower girdle facet and its neighboring bezel or pavilion main facet, and steeper angles of the halves themselves with respect to the horizontal (in which case they are referred to as “dug out” facets). These techniques are well known in the diamond cutting industry, but seldom discussed outside of that group.


Another way to describe this effect is with a term primarily used by colored stone cutters, namely “indexing.” In the design of a given colored stone cut, the position of the center of each facet around the outline of the stone is described in reference to the index wheel used in cutting machines (see, e.g., G. and M. Vargas, Faceting for Amateurs, 3rd ed., publ. by Glenn and Martha Vargas, Thermal, California, 1989). Such wheels come in a variety of scales, dividing the circular outline into, for instance, 64, 80, or 96 steps. “Indexing” is the practice of altering the “standard” positions for some facets – that is, moving their centers slightly in either direction, so that their three-dimensional position is changed. Index wheels usually are not used in diamond cutting because of hardness constraints on the positions and directions of cutting and polishing, but the indexing technique (“painting” or “digging out”) is still practiced (figure A).




Figure A. A tang such as this is used to hold diamonds during the diamond cutting process. By slightly turning the knob indicated, cutters are able to adjust the orientation of the upper and lower girdle facets so that they are “painted” or “dug out.” Photo courtesy of Sofus Michelsen.

Normally, the centers of half facets occur every 22.5° around the girdle. Full polishing of the facets in these positions gives the girdle its evenly scalloped shape (figure B, center). Without changing the lengths of the upper or lower girdle facets, their index positions can be altered by a few degrees, either toward the bezel or pavilion main (figure B, left), or away from them (figure B, right). These changes in position affect the scalloping of the girdle, because they change the area and shape of the half facets, and their angle to the horizontal. If the girdle were a circle with no thickness, crown and pavilion half facets with altered index positions would overlap, and the odd facet shapes that resulted would be glaringly obvious. Instead, the differences in facet shape are subtle, and are only visible from the profile view.




Figure B. The positioning of the upper and lower girdle facets around the circumference of a round brilliant affects the shape of these facets, and hence the shape of the girdle. Normal positioning produces a typical, evenly scalloped shape (center). Moving the index positions toward the bezel and pavilion main facets by 6° each increases the girdle thickness at the “half” junctions, and results in increased weight in the finished stone for the same total depth (left). Changing the positions toward the junctions between the half facets by 3.5° decreases the girdle thickness at these junctions and yields a lower finished weight (right). Note that the girdle thickness at the bezel main junctions (which is the thickness that contributes to the total depth) remains the same in all three cases. Illustrations by Scott Hemphill.

Such changes in the upper and lower girdle facets also affect the weight recovery of the stone. As shown in figure B (left), leaning these facets toward the bezel or pavilion main facets – “painting” the facets – results in a thicker girdle scalloping at the junction between the halves, which yields a greater weight in the finished diamond for the same total depth. “Digging out,” or leaning the half-facet positions the other way (toward the junction between the “halves”; figure B, right), causes the scalloping to change in the other direction (the thickness of the girdle scalloping at the junction between the halves is smaller than the bezel/main girdle thickness) and yields a lower finished weight.


Changing these index positions also changes the angle between the two half facets, and the angle between each “half” and the bezel or pavilion main next to it. Such variations in the inter-facet angles significantly affect the movement of light through the diamond, and thus its overall, face-up appearance. Figure C shows three round brilliants with similar proportions (table 1). These diamonds were photographed in a viewing environment that uses both diffuse white light and a black area that emphasizes the face-up contrast pattern of a diamond (areas of contrast may look different in actual face-up views of diamonds in normal lighting and viewing conditions). Despite the similar proportions of the three diamonds, they display markedly different face-up patterns. These differences are mainly due to the placement of the upper and lower girdle facets.




Figure C. These photos show three diamonds with similar proportions, as described in table 1. However, differences in the relative placement of the upper and lower girdle facets result in different face-up appearances, as evident in this particular viewing environment (areas of contrast may look different in actual face-up views of these diamonds). The diamond on the left shows strong contrast only under the table area. The Hearts On Fire diamond in the center shows a balanced distribution of contrast. The Fabrikant Brilliant diamond on the right displays different areas of contrast, which contribute to a different face-up appearance. Photos by Al Gilbertson.

The round brilliant on the left is a commercial diamond in which the upper and lower girdle facets have been displaced toward the bezels and pavilion mains (as in figure B, left). This diamond shows little contrast except for the dark appearance of the pavilion mains beneath the table. The diamond in the center, from the Hearts On Fire brand, has all its facets – including the “halves” – in evenly spaced positions (as in figure B, center). This diamond shows areas of contrast both under the table and under the eight bezels. The round brilliant on the right, called the Fabrikant Brilliant, has half facets that have been moved toward each other (as in figure B, right), which increases the number of areas of contrast seen under the table and adds eight semicircular areas of contrast around the edge of the diamond. In this case there is a noticeable difference in the location of areas of contrast, which changes its appearance.


The three diamonds in figure C are examples of different diamond appearances that can be achieved within this combination of proportions. Still, other distinct appearances can be created from these proportions by other variations in the placement of the upper- or lower-girdle facets. Truly, every facet matters.


This report was prepared by Dr. Ilene Reinitz and Tom Moses of the GIA Gem Laboratory in New York. For more updates from the GIA Gem Laboratory, see the Lab Notes section of Gems & Gemology. To subscribe to G&G, click here. Or contact Circulation Coordinator Debbie Ortiz, call toll-free 800-421-7250, ext. 7142, or fax 760-603-4595. Outside the U.S. and Canada, you can also call 760-603-4000, ext. 7142.

 

JohnQuixote

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Date: 12/12/2004 9:11:56 PM
Author: Garry H (Cut Nut)
BTW - we should use Painted and Dug Out as the standard terminology - that way we do not get too many words that mena  the same thing


Now where have I heard this charming idea before?
31.gif


What's your position on the "cheated" term now?
 

Garry H (Cut Nut)

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As always John - if the stone is improved by painting or digging, then it is tricked.
If the stones performance is compromised, then it is cheating.

More often we see stones that are slightly steep deep AGS 0''s dug out.

This practice will cease when AGS bring in their new plan to measure girdles at the thick part (as in Europe) rather than the valley''s as GIA do.
 

Paul-Antwerp

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Date: 12/13/2004 1:49:41 AM
Author: Garry H (Cut Nut)
As always John - if the stone is improved by painting or digging, then it is tricked.
If the stones performance is compromised, then it is cheating.

More often we see stones that are slightly steep deep AGS 0''s dug out.

This practice will cease when AGS bring in their new plan to measure girdles at the thick part (as in Europe) rather than the valley''s as GIA do.
I wonder whether the new policy of AGS will show all examples. It will in the case of a specific way of pasting, which you can find in a specific branded cut.

But in most stones, the cutter will work away the high end of the girdle by indexing at their turn the neighbour-facets, and the halves.

Live long,
 
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