here - american gem society laboratories

© 2005 American Gem Society

Foundation, Research Results and Application of the New AGS Cut Grading System

By Peter Yantzer, Jim Caudill, Dr. Jose Sasian


This presentation is divided into three sections: Foundation, Research Results, and Application / Methodology.

The Foundation information will detail our understanding of diamond cut.

The Research Results will show you what we found with respect to the Round Brilliant and the Square Princess Cut.

The Application / Methodology section will explain the new AGS Cut Grading System.


Foundation


The new AGS System will take into account the following factors: an observer, a close viewing distance, obscuration, contrast, appearance as distance varies, brilliance, fire, leakage, scintillation, weight ratio or ‘spread’, tilt, girdle thickness, length-to-width ratio, polish, symmetry, durability and taste.

In April 2002 at the AGS Conclave in Vancouver B.C. we proposed:“An Ideal Cut Diamond performs better than other similarly cut diamonds over the broadest range of usually encountered lighting and observer conditions. Because the lighting and the observer circumstances so greatly effect the perception of a diamond’s beauty, they must be considered in relation to the diamond’s proportions when assessing cut quality.”

Premise: In order to build grading systems and teach them, assumptions and simplifications must be made.


During the course of this presentation you’ll be seeing images:

Our ray tracing software gives us various values and can also color code the angular ranges from which a diamond draws light.

The ASET is our Angular Spectrum Evaluation Tool and we pronounce it like the word ‘asset’. It allows us to take color-coded photographs of actual diamonds.

DiamCalc is a software program created by the OctoNus Company at Moscow State University in Russia. It has an abundance of features that allows us to model virtual diamonds, as well as model ‘skin’ maps or wire frames of real diamonds.


Here are images that show the angular ranges and their color code:

Top or Bird’s Eye View


Side View


Result


Assumptions for Average Human Being and Closest Observation Point

We have defined a human observer as the average of a 5th percentile female and a 95th percent male. Reference MIL-STD-1472D:

We set the close observation point at 25 cm. This is the “distance of most distinct vision.”References:http://www.books.md/N/dic/nearpointoftheeye.phphttp://www.swc.cc.ca.us/~jveal/PHYSICS/Phys274/thin_lenses.htmhttp://badger.physics.wisc.edu/lab/manual2/node19.html

http://www.books.md/N/dic/nearpointoftheeye.php

http://www.swc.cc.ca.us/~jveal/PHYSICS/Phys274/thin_lenses.htm

http://badger.physics.wisc.edu/lab/manual2/node19.html

http://badger.physics.wisc.edu/lab/manual2/node19.html


Here is the geometry of our average human observer viewing a diamond:

Because of the difference between whole head obscuration and thedistance to each eye, we assume a cone of 30 degrees at 25 cm. We also evaluate a diamond’s appearance using a cone of 40 degrees at 25 cm.


Obscuration

The act or operation of obscuring; the state of being obscured; as, the obscuration of the moon in an eclipse.Reference: http://dictionary.reference.com/search?q=obscuration

In order to simplify the complex relationship of a viewer, the surrounding environment, and the diamond’s proportions, we propose the concept of obscuration. There is no doubt that an observer greatly influences a diamond’s appearance when he or she is viewing it. Additionally, the surrounding environment can obscure.

Premises: Obscuration is the primary producer of contrast. The observer’s head is the most common cause of obscuration.

http://dictionary.reference.com/search?q=obscuration


Diamonds do not possess much inherent contrast. Here’s a simulation of the Tolkowsky model ( p4075t53c345s50lg78 ) in isometric lighting without the presence of a viewer at 25 cm:

Face Up 5 degree tilt 10 degree tilt


Looking at the same stone, we’ll add a 30 degree cone of obscuration:


The Observer’s Head

Our ‘average’ human being’s head obscures a cone of 30 degrees or plus/minus 15 degrees from the normal (perpendicular to the table facet) at 25 cm.

Our ‘average’ human being’s head is circular in shape.

Assumption: The ability to discern differences in diamond cut quality decreases as the distance from the observer’s eyes increases.


The Observer’s Body

The observer’s body also obscures a diamond.

In a typical viewing scenario, the closer a diamond gets to an observer’s body, the less the effect produced by the observer’s body.

Or to say this another way, as distance increases, the effect of an observer’s body increases.

This may seem paradoxical, so let’s look at a typical viewing scenario.


The Observer’s BodyThese viewers are looking at a diamond at about 10 inches from their eyes.

As you can see, the observers’ bodies obscure somewhere between 30 and 40 degrees of lighting that may be coming from behind them.


The Observer’s BodyHere’s what happens to that angular relationship at a viewing distance of 16 inches.

Now the observers are obscuring somewhere between 40 and 50 degrees.


ContrastPremise: Contrast can produce positive and negative optical effects.

Humans are ‘hard wired’ to detect edges. Contrast provides us with these edges. Here’s an example of a shape with virtually no contrast and the same shape with contrast. Humans find the image on the right to be very appealing compared to the left. Other researchers on diamond cutting have pointed out that the presence of contrast enhances our perception of diamond brilliance. We agree.


Humans are sensitive to the amount and distribution of contrast.

Examples of too little and too much contrast:


Poor distribution of contrast:


FrequencyWe are also ‘hard wired’ to find certain frequencies appealing.

When shown this frequency chart, the majority of people will pick a spot close to the area marked in red as being the most appealing. Weinstinctively find the frequencies to the left as being too broad and the frequencies to the right as being too narrow. In addition to contrast, frequency has implications for scintillation as well.


Let’s apply a 30 degree cone of obscuration to different round brilliant cut diamonds:

41.1 Pavilion Angle Tolkowsky Nail Head

Negative – Positive Effect Negative – too much no primary contrast


We have named two types of obscuration induced contrast – primary and secondary. Primary contrast is the face up and/or stationary view and therefore static in nature. Secondary contrast is the light/dark pattern as the stone moves and is dynamic in nature.

Below is an illustration of how the primary contrast at 25 cm varies with amount of the angular obscuration for the Tolkowsky model.

~21 degrees ~25 degrees ~44 degrees ~47 degrees

No effect Positive effect Still Positive Negative effect

It is evident that the Tolkowsky model handles a large range of obscuration in a positive manner. Most importantly, it handles this obscuration in the range a human observer’s head (30 degrees) provides. Or, you may say that it accommodates, in a positive manner, a wide range of different head sizes.


Examples of secondary contrast using 30 degrees of obscuration at 25 cm:

4 degrees of tilt 5 degrees of tilt 6 degrees of tilt 7 degrees of tilt

8 degrees of tilt 9 degrees of tilt 10 degrees of tilt 11 degrees of tilt

1) Very little happens to the light/dark pattern in the first 4 to 5 degrees of tilt.

2 As the optical ‘windows’ or compound mirrors go from light to dark and back to light, you see fire.

Assumption: Contrast also enhances our ability to see fire.


As you have seen, contrast is a two edged sword – too little, too much, or poor distribution is ‘bad’. The right amount with pleasing distribution is ‘good’. Contrast is a very important aspect of diamond appearance.

Fortunately, contrast in the standard round brilliant is independent of table size. It’s a function of crown and pavilion angles, influenced slightly by star and lower girdle height. This allows us to create an obscuration chart:

In fancy shapes, the contrast produced by obscuration is unique to each cut. It is, however, very important to assess the effect of obscuration for each shape.


Diamond Appearance as Distance Increases

Assumption: The ability to discern differences in cutting quality decreases as distance increases. Our starting point is 25 cm or 9.84 inches.

Premise: As distance increases, the effect of an observer’s head decreases.Tolkowsky at 25 cm at 40 cm at 80 cm

p4075t53c345s50lg78

Inferior make at 25 cm at 40 cm at 80 cm

p393t55c330s50lg80


The previous slide demonstrates that an inferior make can look quite good as the distance increases between your eyes and the stone.

Great makes look great both ‘up close’and far away. Inferior makes are readily discernable as inferior ‘up close’.


Brilliance

Assumption: The world is lit from above.

The terms ‘brilliance’ and ‘brightness’ are not interchangeable in this presentation.

By color-coding angular ranges ( green = 0 to 45 degrees, red = 45 to 75 degrees, blue = 75 to 90 degrees from the horizon) we can model where diamonds gather light.


Tolkowsky Fish Eye Nail Head

p4075t53c345s50lg78 p370t62c345s50lg78 p440t62c345s50lg78

Well made round diamonds gather a large portion of light from the angular range of 45 to 75 degrees from the horizon. This is the area where a diamond is most likely to find direct sources of light and that light will miss the observer’s head and body. In the above illustration, you see that a fish eye also gathers a large portion of light from this range and yet it is universally accepted to be an inferior make. So it’s obvious that brightness alone does not complete the description of brilliance.


Many fancy shapes don’t gather a large portion of light from this range and they tend to leak a lot of light. Here are examples of an oval and a princess cut. The color-coded images here are backlit to show the white leakage areas. The photo real images are not backlit.


We know from experience that well made rounds are brilliant. We also know that fancy shapes can appear brilliant as well. So it seems paradoxical that we can perceive both as being brilliant when the round gathers a majority of high quality light ( red ) and some fancies gather a large amount of low quality light ( green ).

Brightness is relative. Our brain innately and constantly adjusts levels of brightness to make sense of what it ‘sees’. This is just like the auto exposure control on a camera, except humans do it better and faster. We can observe in the above examples that differences in brightness set up areas of contrast. You might call this ‘brightness contrast’. It’s this effect that can produce a pleasing ‘look’ and the stone will appear to be brilliant to us.

Therefore, in our opinion, there are three things that affect our perception of brilliance:1) Brightness2) Contrast caused by obscuration3) Contrast caused by changes in brightness

It is not so important to measure brightness but more important to understand that brightness is relative, and if combined with positive obscuration contrast effects and/or positive brightness contrast effects, the stone will appear brilliant.

We are defining brilliance as: brightness with positive contrast effects.


The Illumination of Great Diamond Design

The most desirable angular range is 45 to 75 degrees.

Why? 1) Because it misses the observer’s head and body. 2) This is where the diamond will most likely find

direct sources of illumination.


FireThe perception of fire is accentuated by the presence of multiple spot light sources.

The perception of fire is diminished by the presence of broad diffuse light.


Since lighting environments change constantly, we measure dispersion.

First, we divide the diamond into three zones of equal area:


Next, we ray traced hundreds of thousands of virtual and wire frame models and averaged the dispersion for each zone at a viewing distance of 25 cm.

Here are the dispersion values ( in millimeters ) for the Tolkowsky, Fish Eye and Nail Head stones shown earlier in this presentation.

Tolkowsky Fish Eye Nail HeadTable 3.7 1.6 0.8Inner Bezel 2.8 2.7 4.4Outer Bezel 3.8 2.6 6.0Average 3.4 2.3 3.7

Finally, we analyzed the data looking for relevance. Indeed, we did find relevance. Industry accepted fine makes produced high values across all three zones while inferior makes suffer in one or more zones.

As an aside, we initially looked at the average dispersion across the entire crown. What we found was that a very high reading in one zone could skew the average. We concluded that an entire crown average was useless.Here’s an example:p420t55c385s50lg78Table 2.1Inner Bezel 4.0Outer Bezel 7.0Average 4.4


We postulate that diamonds with high-dispersion-averages across all three zones have the greatest potential to exhibit fire.

This becomes more important as viewing distance decreases.

there are primary (static) and secondary (dynamic) states.

We look at fire similarly to contrast in the sense that


LeakageIn the bulk of our studies, no light was allowed to interact through the pavilion or girdle plane. Or, to state another way, light was only allowed to interact through the crown facets and table.

Assumption: small amounts of leakage is essentially inconsequential. Large amounts of leakage, typically occurring in some fancy shapes and some standard round brilliant proportion sets, is detrimental.

Leakage is readily quantifiable and can be factored into a grading system.In these color-coded and ray-traced examples, leakage is quantified and shown in white.

Fine Make 5.1% Fish Eye 11.0% Nail Head 28.9%

It should be noted that leakage is one of the two vehicles whereby brightness contrast effects are produced. The other is the size and distribution of areas that draw light from low angles – the greens in these images. These brightness contrast effects can be positive or negative.


Scintillation or Sparkle

Here are a couple of definitions of scintillation:GIA Diamond Dictionary, 1977 EditionScintillation in gemstones can be defined broadly as an alternating display of reflections from the polished facets of a gemstone seen by the observer as either the gemstone, the illuminant or the observer moves; it is a flashing or twinkling of light from the facets. Comparative scintillation, or the degree of scintillation in a diamond, is determined by (1) the number of facets on the stone that will reflect light to the eye as the stone is moved about (i.e., the number of individual reflections), and (2) the quality of the polish of the facets, since the more highly polished the facets, the brighter the reflections and hence the stronger the flashes from them.

GIA Diamond Dictionary Online, http://giaonline.gia.edu/public/cgi/as_web.exe?dia_dic.ask+FFlashes of light reflected from a polished diamond, seen when either the diamond, the light source, or the observer moves. Besides diamond's inherent optical properties, scintillation depends on the number and size of the facets, the precision of the facet angles, and the quality of the polish. Sometimes called sparkle.


Earlier in this presentation we stated that the light/dark areas changed very little over the first 4 to 5 degrees of tilt. Here’s an example:

0 1 2 3 4 5 degrees


Let’s put the Tolkowsky model in a lighting environment that allows us to see what happens with fire:

0 1 2 3 4 5 degrees

Depending on relative lighting conditions, you may not be able to resolve these as fire, only as a sparkles. That’s because the brightness may be overpowering your ability to discriminate.


As you can see, the changes are abrupt and dramatic. They occurover very small changes in angular displacement.

We believe that any definition of scintillation should include white and colored sparkles. We also believe that fire-in-motion or dynamic fire is a strong component of scintillation.

Adding fire-in-motion as a component of scintillation requires that a diamond have a high potential (dispersion) to produce fire in order to generate high scintillation.

From a common sense and practical standpoint, this consolidationof white and colored sparkles into the definition of scintillation probably best describes what diamantaires have called ‘life’.

We propose the following as a definition of scintillation:The sparkle of white and colored flashes seen as the stone and/or the observer and/or the light source(s) move.


Scintillation - Continuing Research

We continue to research scintillation. Here’s what we believe at this point in time. The trick is in measuring it or creating a metric for it.Scintillation is a function of the double reflection pattern of a faceted diamond. We call these compound mirrors.


Scintillation - Continuing ResearchYou can change the amount of scintillation in a faceted

gemstone in two ways that we know of: 1) Add more facets.2) Change the size of the facets, thereby changing the

compound mirrors.This is an example of adding facets ( facet arrangement

on left, compound mirrors image on right):


Scintillation - Continuing ResearchThese examples show the compound mirrors for the Tolkowsky

proportion set but with changes in the length of the stars and height of the lower girdle facets.

35% Star 50% star 50% star60% lower girdle 80% lower girdle 90% lower girdle

Image 1 Image 2 Image 3


Scintillation - Continuing ResearchImage 1 is a classic Old European cut. These stones were known for

big, broad flashes of fire with less scintillation than today’s modern round brilliant.

Looking at the compound mirrors, you can see why.


Scintillation - Continuing ResearchImage 2 is a modern round brilliant. Over time, cutters lengthened

the stars and lower girdle facets. The net effect is more scintillation with good perception of fire. Research by scientists at Moscow State University postulate that a well cut stone should

have a nice balance of large and small compound mirrors.


Scintillation - Continuing ResearchImage 3 shows the effects of too long lower girdle facets. The compound mirrors are similar in size and the lower girdle facets

overpower the table area. The net effect is that scintillation may be higher but there is lower dispersion in the outer bezel and

contrast is adversely affected.


Scintillation - Continuing ResearchWith excellent performance to begin with, you might say:Big compound mirrors = big fire but small scintillationSmall compound mirrors = small fire but big scintillation.

Dynamic contrast + dynamic fire = scintillation.

The new AGS Grading System handles scintillation passively, and depending on the outcome of our continuing research, probably sufficiently. Here’s how: if the lower girdle facets get too short, contrast becomes a negative factor. If the lower girdle facets get too long, contrast and dispersion suffer.

You probably deduced that it is not necessarily the number of compound mirrors, but the balance and distribution of large and small compound mirrors in any given cut that matters.

You may also have speculated that different size compound mirrors may enhance diamonds of different size - .50 ct vs 2.00 ct vs 7.00 ct., for example. This may lead to new faceting arrangements based on physical size.


Weight Ratio or ‘Spread’‘Spread’ is an industry term that refers to a diamond’s face up size compared to its weight. You can also call this ‘weight ratio’ or ‘millimeter footprint versus weight’.

The classic example is that a fine make 1.00 carat round brilliant cut diamond should have a ‘spread’ of about 6.5 millimeters. Naturally, you would want to purchase the largest millimeter stone that weighs the least amount and still performs. Why pay for unwanted weight?

For a one-carat diamond, the current AGS Ideal 0 proportions allow a millimeter ‘spread’ range of 6.30 to 6.57 mm.


Most people would not consider a 1.00 carat round brilliant cut diamond with a ‘spread’ of 6.30 millimeters to be an Ideal.

Therefore, we are using a 5% ‘spread’ factor for the round brilliant in our new grading system. We are normalizing to the Tolkowsky cut with a 2.7% girdle thickness at the mains and 1% at the scallops. This Tolkowsky model will weigh 1.00 carat at 6.47 millimeters in diameter.

A tight ‘spread’ tolerance is a beautiful thing because it self corrects a lot of cutting faults.

Cutters know how to ‘swindle’ our existing proportion sets to maximize weight at the expense of beauty. We hope that the ‘spread’ component will go a long way in furthering the world diamond community’s and consumer’s perception of fine make. It’s also reasonable in today’s world of precision diamond cutting. Lastly, it’s easy to teach and understand.


Indexing the Upper Half Facets on a Round Brilliant Cut

‘Normal’ cutting produces equal girdle thickness at the junction of the mains and the half facets.


Indexing the Upper Half Facets

Cutting the upper halves on a non-normal index results in girdle thickness that is different at the halves than at the mains.

Example 1 Example 2Thicker at Mains Thicker at Halves



Example 1 can result in better weight retention but at the expense of optical performance.

AGS ASET ‘Hearts & Arrows’ Fire Scope

Brightness simulation



Example 2 can result in less weight retention but face up leakage is eliminated.

AGS ASET ‘Hearts & Arrows’ Fire Scope

Brightness simulation



Example 1 can be an AGS 0 in our existing system. It will not be an AGS 0 in our new system.

Example 2 can be an AGS 0 in either system.

The AGS ASET provides, at a glance, much more information than other types of viewers.

A complete article on this topic is included on this CDRom disk.


TiltGeorge Kaplan wrote a letter to Gems and Gemology and it was published in the Summer 2002 issue. In that article he made a case for the concept of the ‘Cone of Beauty’. He said that a well made round brilliant can stand a larger amount of tilt before the girdle is reflected in the table of the stone. As an example, his firm cut two identical diamonds except one had a 55% table and the other a 65% table. With a tilt of 10 degrees, the 65% tablestone started to show dull girdle reflections in the table. On the other hand, the 55% table handled a tilt of 18 degrees. Therefore, he said that the 65% table stone had a ‘Cone of Beauty’ of 20 degrees. The 55% table stone had a ‘Cone of Beauty’ of 36 degrees.

We support George Kaplan’s astute observation and think it should be part of our new grading system. It’s another factor that helps to separate fine makes from inferior makes. It’s also another factor that adds to the concept of an Ideal.


Tilt Examples It’s easy to make tilt charts for the standard round brilliant. Westarted with the Tolkowsky model and verified what it looked like at 18 degrees of tilt. In order to build a grading system, we needed to ‘relax’ that number while still maintaining the same ‘look’. 14 degrees of tilt seems to be realistic.

Tolkowsky @18 degrees of tilt 59 table at 14 degrees of tilt.

Girdle reflection shown in green


Tilt Charts Table % Minimum Pavilion Angle

47 39.048 39.149 39.250 39.451 39.552 39.653 39.754 39.955 40.056 40.157 40.258 40.459 40.560 40.661 40.762 40.963 41.064 41.165 41.366 41.467 41.568 41.669 41.770 41.9


Girdle ThicknessOur research has shown that the only good things about a girdle are:1) it defines the shape of the stone.2) if it is sufficiently thick, it helps to prevent chipping.

Other than that, the girdle is an area that allows detrimental infiltration and leakage of light.

Here are color-coded, face up simulations of the Tolkowsky model and photo realsimulations of their profiles.

very thin thin medium sl. thick thick very thick ex. thick


TasteWith respect to the standard round brilliant, the three areas of taste are:

Table reflection

Width of Pavilion Main facets

Table Size


Some fancy shapes can offer a wide variety of equal performance with different ‘looks’.

Here are some Princess cuts.55% Table

65% Table

70% Table

The new AGS grading system allows for taste factors.


Insights Gained Using the AGS ASETWhy Older Cuts Have Short Star Facets

Before the invention of the diamond saw, the diamond’s table was fashioned by grinding away one of the points on an octahedron. In

order to save weight, small table sizes were the rule.


Insights Gained Using the AGS ASET

Cutters are very, very smart. These ASET images show you why cutters shortened the star length when making older cuts.

P410t47c358s50lg60

Crown ASET Brightness Sim Profile

It’s readily apparent that the 50% star length makes the upper halves too steep. Performance suffers.


Insights Gained Using the AGS ASET

See what happens when the star facets are shortened to 35%:P410t47c358s35lg60

Crown ASET Brightness Sim Profile

Shorter star facet length lowers the angle of the halves so they draw light from the red area. Performance is greatly improved.

In this case, looking at the past helps to validate the present.


Lower Girdle Height

We measure lower girdle length by height. This is the same as the OctoNus DiamCalc software.

GIA measures lower girdle length by radius. That way you can measure it with a table gauge.

It can cause confusion because the two aren’t identical.


Lower Girdle Height – AGS / DiamCalc to GIA Conversion Chart

Special thanks to Bruce Harding and Jason Quick


Lower Girdle Height – GIA to AGS / DiamCalc Conversion Chart

Special thanks to Bruce Harding and Jason Quick


Foundation Summary

• Studied the effects of an observer, surrounding environment, and lighting.

• Studied how humans ‘see’ our world.• Developed metrics that reflect actual

observation.• Invented new tools.• Proposed new definitions.• New system is three-dimensional in nature.


Research Results


The Round Brilliant

• Tolkowsky’s Five DiamondsStone 1 Stone 2 Stone 3 Stone 4 Stone 5 Average Theoretical

Diameter 7.00 7.08 6.50 21.07 9.12

Depth 4.12 4.35 3.61 12.34 5.47

Pavilion Angle 40.75° 40.75° 40° 41° 41° 40.7 40.75

Pavilion Depth % 43.0 42.8 42.1 42.8 42.2 42.6 43.1

Crown Angle 35° 35° 34.5° 33° 34° 34.3 34.5

Crown Height % 15.7 18.6 13.3 15.7 17.8 16.2 16.2

Girdle Thickness v. thin v. thin v. thin v. thin v.thin

Est. Table % 55 47 61 52 47

Est. Weight 1.23 1.31 .94 33.26 2.77


Their Appearance with 50% Star Length, 80% Lower Girdle Height

1 2 3 4 5


Conjecture

• If Tolkowsky had the tools we have, he might have picked this one for his Stone #3:

• P411t61c329s50lg80


Why Now?

• Fast computers, accurate measuring devices, ray tracing software, OctoNus DiamCalc software.

• Advanced science and technology allows us to grade the diamond in three-dimensional space rather than two-dimensionally.


Explanation of Charts

• In case it’s hard to read them, the following charts are set up in the following manner:

• Pavilion angle is 43 degrees in the top left corner and descends in 0.2 degree increments to 39.8 degrees in the bottom left corner.

• Crown angle starts at 29 degrees in the top left corner and increases in 0.2 degree increments to 40 degrees in the top right corner.

• The charts are for a 6 millimeter diameter stone, 50% star length, 80% lower girdle height, and a 3.5% girdle thickness at the mains.


Findings• Combined overlays:

• Tilt, Weight Ratio, Contrast, Durability

• You’ll notice that we’ve defined an area for potential 0’s for a 55% table without knowing anything about brightness, dispersion, or leakage.


Defining the New AGS 0

• The previous chart with the candidates for a 55% Table.


Candidates

• The reason we use the word ‘candidates’ is because the entire system is dynamic. For example, contrast changes with size.

• The boundary edges are ‘fuzzy’ in the sense that a cutter can bring a borderline stone into a higher category by adjusting star length and lower girdle heights. A cutter can also adjust girdle thickness to bring some stones into a higher grade if itsgrade is being reduced by the weight ratio factor.

• You can also lower a candidate through sloppy cutting or indexing the facets, especially the upper girdle facets.

• To consistently produce a desired cut grade, cutters will have to cut to ‘fat’ portions of the charts.


Round Brilliant Cutting Guideline Charts for Table

Sizes 47 through 70%

All of the following charts are included on this CDRom disk


Special thanks to Jake Sheffield for the charts


The Old and the New

• 55% Table

• The steep pavilion - steep crown and the shallow pavilion - shallow crown corners of our existing two-dimensional system will no longer be AGS Ideal 0’s.


Star Length• This chart shows the effects of changing the star length for a

6mm round brilliant, cut normally with a 55% table:

• Shortening the stars to 40% increases the candidates by almost 25%.• Lengthening the stars to 60% reduces the candidates by over 75%.


Lower Girdle Height• This chart shows the effects of changing the lower girdle height for a

6mm round brilliant, cut normally with a 55% table:

• Shortening the lower girdle facets to 75% decreases the candidates by about75%.

• By increasing the lower girdle facets height to 85%, the number of candidatesremains about the same, but shifts slightly up and to the left.


Opportunities

• Candidates in new table sizes. • Better weight retention and weight

ratio options.


What’s Ahead

• More research for smaller diamonds– Diamonds under 15 points not eligible for

grading

• Commercial and Industrial AGS Software – Batch processing with industrial version


The Princess Cut

• Our new methodology will enable us todevelop cut grading systems for anyshape and facet arrangement.


Configuration• New grading system for square princess cuts

– Bezel Corner– French Corner

Bezel Corner - 45 Facets French Corner - 41 Facets


Complexity

• Princess cut more complex– Two pavilion main angles and two crown

main angles.– Increases combinations exponentially.

Not really exponentially, but a whole lot.‘Exponentially’ sounds better than ‘awhole lot’ and I couldn’t think of a betterword.


Example


Versatility

• Very wide range of table sizes.• When tilted, girdle reflections under

the table are broken up into smallpieces.


Top Performers

• These charts are for a 6 millimeter square with 2 rows of chevron shaped facets on the pavilion.


Macro Chart

All of the macro Square Princess Guidelines Charts are included on this CDRom disk.


55 Appearance


55 Cutting Suggestion


Micro View of 55 Table Guideline Chart


60 Appearance


65 Appearance


70 Appearance


75 Appearance


Top Performer Distribution By Table Size


AGS Grade Distribution


Application / Methodology

The New AGS Cut Grade System


Introduction

• Software driven system.• Combination of deduction and net

lowering categories.• Complex set of criteria is evaluated to

establish a grade.


Expression

• Same AGS cut grade format.• Modified sub-categories.

Cut Grade AGS Ideal 0Light Performance 0Proportion Factors 0Finish 0


Sub-Category 1

• Light Performance– Brightness– Dispersion– Leakage– Contrast


What’s Going On Inside the AGS Software?

• The following slides will simulate grading for a Round Brilliant Cut diamond with a 55% Table, 50% star length and 80% lower girdle height


Brightness Deduction Charts• Face up, tilted 15 degrees and overlay


Dispersion Deduction Charts• Face up, tilted 15 degrees and overlay


Leakage Deduction Charts• Face up, tilted 15 degrees and overlay


Contrast Deduction Chart• 30 degree obscuration, 40 degree

obscuration and overlay


Overlay Result

• The 55% table round brilliant cut diamondmust fall within the white area of this chartto be an AGS Zero candidate


Sub-Category 2

• Proportion Factors– Girdle Thickness– Culet Size– Weight ratio or millimeter footprint versus

weight or ‘spread’– Durability ( Crown Angles less than 30

degrees )– Tilt ( at what point does the girdle reflect

under the table )


New Girdle Thickness Chart*

* Reflects AGS Diamond Grading Standards ChangeEffective May 1, 2013


Net Lowering Chart

Culet Size – same as before

Culet Size AGS GradePointed, Very small, Small, Medium

0

Slightly large 1Large 3Very large 5Extremely large 7,8,9,10


Weight Ratio Deduction Chart


Durability Deduction Chart


DurabilityTraditionally the industry discounts diamonds with extremely thin and very thin girdles. We also do the same. The other durability factor that we do not address is shallow crown angles. Industry wisdom says that a diamond with crown angles under 30 degrees is more likely to break under normal wear and tear. GIA currently issues a statement on its reports if the crown angle is less than 30 degrees.

We’ll address shallow crown angles in our new system.

Here’s an example of a round brilliant with high, but not the highest performance and crown angles of less than 30 degrees:

p416t55c296s50lg78


Tilt Deduction Chart

55% Table


Sub-Category 3

• Finish– Polish– Symmetry


Net Lowering Chart*

• Polish and Symmetry

AGS Ideal® (0) Cut GradeLight Performance /

Proportion Factors Polish Symmetry Numeric Designator

Ideal (0) Ideal (0) Ideal (0) 0 0 0 The Triple Zero®

Ideal (0) Excellent (1) Ideal (0) 0 1 0

Ideal (0) Ideal (0) Excellent (1) 0 0 1

Ideal (0) Excellent (1) Excellent (1) 0 1 1

AGS Excellent (1) Cut Grade Light Performance /

Proportion Factors Polish Symmetry Numeric Designator

Excellent (1) Excellent (1) Excellent (1) 1 1 1

Excellent (1) Very Good (2) Excellent (1) 1 2 1

Excellent (1) Excellent (1) Very Good (2) 1 1 2

Excellent (1) Very Good (2) Very Good (2) 1 2 2

This Cut Grade model continues for Very Good, Good, and so forth.

* Reflects AGS Diamond Grading Standards ChangeEffective November 15, 2012

The AGS Ideal® (0) Cut grade is attainable with Ideal or Excellent polish and symmetry grades as follows:


Deduction vs. Net Lowering

• Cumulative deductions– Brightness, Dispersion, Leakage, Contrast,

Durability, Weight Ratio, and Tilt– Add them up or sum them. I.e. 1+1+1 = 3

• Net lowering deductions– Girdle Thickness, Culet Size, Polish and

Symmetry– They only lower the cut grade if lower than the

sum of the deductions

• Software performs calculations


Length-to-Width RatioWe have had much discussion on what length-to-width ratios should be included in our new system.

The existing AGS Diamond Standards specify acceptable length-to-width ratios for various fancy shapes.

Here are the ratios for some fancy shapes:Oval length to width range: 1.33 to 1.66


Length-to-Width Ratio

Emerald Cut length to width range: 1.50 to 1.75



Marquise length to width range: 1.75 to 2.25



Pear length to width range: 1.5 to 1.75


How Do I Cut Grade a Diamond?

• Step by step demonstration.• Mostly software automated.


Step One

• Measure the diamond with a machine.• Create a three-dimensional model.• Does require a hardware investment.


Step Two

• Import three-dimensional image intoAGS Software and ray trace.

• Optical performance is measured.

Pavilion angles

Crown angles Table

Star Length

Lower girdle

T Dispersion T value

I Dispersion I value

O Dispersion O value Blues Reds Greens Leakage

40.75 34.5 53 50% 78% 1.0 21.2 1.0 19.9 1.0 27.4 21.2 66.2 7.2 5.4

15 degree T

Dispersion 15 degree T value

15 degree I Dispersion

15 degree I value

15 degree O

Dispersion15 degree O value Blues Reds Greens Leakage

0.9 21.9 1.3 22.9 1.0 19.0 11.4 64.9 18.5 5.2


Step Three

• Software will compare values and assign adeduction grade.

• Software will compare values to net loweringcategories and adjust.

• Grader inputs polish and symmetry grades,verifies girdle thickness and culet size.

• Software assigns light performance portionof final cut grade.


Don’t I Get To Do Anything?

• Check or verify girdle thickness andculet size.

• Evaluate polish and symmetry.• You may have to assess contrast on

some fancy shapes.


Easy as 1, 2, 3

• The new AGS Cut Grading System is the mostsophisticated system ever developed.

• Even so, it is the easiest AGS system to use –ever.

• Most importantly, the methodology can beapplied to any shape and facet arrangement.


Wait, There’s More

• Research on rectangular Princess Cuts and impact of more ‘chevron’ shaped facets.

• Results in very near future.


Afraid of Diamond Commodities?Let’s Revisit ‘Taste’

• Most of us probably feel that a diamond commodityis a bad thing.

• Some are afraid that this new grading system willmake diamond a commodity.

• The research only quantifies what experiencedpeople already know.

• You and your expertise are still the most importantpart of a diamond sale.

• Let’s look at some examples of different AGS Gradesand you decide for yourself.

• The following examples have 50% star length and80% lower girdle height.


Afraid of Diamond Commodities?AGS 4 Cut Grade

• P410t65c298 P426t51c324



• P418t49c338 P416t68c304



• P400t55c382 P412t63c302



• P412t58c322 P402t55c372



• P418t47c338 P412t61c328


Afraid of Diamond Commodities?Conclusion

In this case, seeing is believing. I submit that the new AGS Grading System does more to keep diamonds from becoming a commodity than anything else others have proposed.

I believe that the cutting community is looking at vast and broad opportunities because of the new AGS system.

You are empowered by knowing that equivalent grades are equivalent in performance but different in look ( taste ).

You can empower your customer, get them into your store, and make more sales by asking them what their taste is in an Ideal, or a Very Good, or a Good cut.

The new AGS Cut system will serve you well, if you learn it.

The ball’s in your court.


Thank You!

Special thanks to JCK and all involved in this historic project

here - american gem society laboratories

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