|
| |
An In Depth Look at the Upcoming GIA Cut
Grading System
By Jonathan Weingarten (aka Rhino)
In the Fall 2004 Issue of Gems and Gemology, the GIA has released the specs of
various diamonds and the grading classifications they are going to receive in
their new and upcoming cut grading system. The GIA has been working with ray trace
software to help determine their metrics along with the observance of many
layman and professionals within the diamond trade and have provided 3 sample diamonds
within each of their 5 cut grades which will be released mid 2005.
Using a similar type of software (courtesy of MSU) we have re-created a sample
database consisting of the same diamonds they discuss in this issue. In
addition, we will
be including graphics that demonstrate the characteristics they are describing
for each diamond along with sample .gem files of each (for you to open and
compare) as well as my own commentary and experience regarding the optical
properties of the diamond in question.
What is nice about this is the GIA has included sufficient minor facet
information on each diamond to not only give a basic exam but to provide a more thorough
one as they have come to realize the importance of minor facet cutting to the appearance of
diamonds. For a thorough discussion on the minor facets (consisting of 40
out of 57 facets total) please consult our tutorial on the subject
here.
The metrics GIA will include for the overall Grade will be
those of
- brightness
- fire
- scintillation
- weight ratio
- durability
- polish
- symmetry
The total grade of the diamond will be determined by the
lowest scoring factor. With regards to the major labs ... the bar is being
raised.
To be able to download and view the Gem Advisor files
included in this tutorial you'll need to download the free Gem Advisor software
via this link.
After you install the software you'll also need to open it up and open the
sample file included. When you do this Windows will associate all .gem
files and automatically open the files with the correct program. After you've
completed these steps, to open a Gem Advisor file in this tutorial simply click
on the MSU graphic included in the tables below.
Part 1 - Grade 1
Grade 1 - Example 1 -
RD01
|
|
| Here is a diamond that is typical of
what we purchase for inventory. I generally like my
lower girdles a little longer but you'll find stones in
our inventory that are comparable to these stats that
are just downright beautiful. Amongst the H&A community this particular
stone resembles a certain percentage of unbranded H&A's.
There are many similarities to these particular sets of
angles & %'s to that of an 8starz Diamond, yet not
quite. An 8starz (or one cut similarly) will have
closed off or eliminated all blatant whites (thus
eliminating all leakage) and the little eight pointed
star in the center will also come to 8 perfect points.
The examples given for GIA's top grades reveal one
important factor. They are not cherry picking to the
level/degree of certain super ideal cut retailers or
factories who feature such products (ie. like us!), at
least with regards to optical symmetry (the H&A optical
pattern/design). Another important fact to point out
for those who have read and are fans of Fred Cuellars
(questionable) book on how to buy a diamond ... Fred
counsels his readers NOT to purchase diamonds with
depths over 61%, yet here we have GIA's top grade class
for cut and it's depth is 61.2%. Another point of note
is that GIA will not be making the separations it
appeared they were going to regarding the lower
girdles. In their report on DCLR (dispersed colored
light return) they had concluded that the
lengthening/shortening of the lower girdles
dramatically affected the diamonds appearance with
DCLR increasing as lg length increased. Perhaps they
will deem all lg lengths from 75%
up to 85% in the same
"Grade 1" category (or at least up to a certain
percentage)? |
|
|
Grade 1 - Example 2 -
RD08
| Diamond Stats |
Pic 1: MSU Jewelry Store Lighting |
Pic 2: Simulated LightScope Results |
GIA Image RD08 |
Table: 57%
Crown>:33.5°
Pavilion>:41.2°
Stars: 55%
lower gird: 85%
girdle: medium
culet: none
depth: 61.1%
polish: VG
symmetry: VG |
 |
 |
 |
|
|
| Drastically different minor facet combo here
primarily due to the lower girdles which in this example are increased
in length a full 10% (from 75% to 85%). There are paler reds under
the table indicating light being returned at a weaker intensity in that
location however more blacks are indicative of more light being returned
at higher angles which compensate. As in the first example all
facets are primarily functioning in the role of "mirror" (as opposed to
windows) giving what GIA considers to be an excellent
distribution of light. This diamond is also an excellent example of a
"non-traditional" set of proportions that would have not received the
"ideal" grade from the current AGS grading system. Crown angles of
33.5° would have caused it to
receive a less than ideal grade. With this diamond GIA is
demonstrating that you can get "ideal" brilliance from a set of
proportions that are not traditionally considered to be "ideal" and they
are to be applauded for this. MSU concur the results with
excellent scores for brilliance/light return however the HCA rates the
diamond with an undesirable score over 2.0 (2.5 in this case). In
this circumstance I would take sides with GIA/MSU as the light being
returned is sufficient to qualify for a Grade1 classification.
If one were to compare these first two diamonds side by side there *can*
be notable optical differences. The first diamond is generally
described by observers as having fewer, yet broader/bolder flashes of
light while this 2nd example having more tinier points/flashes of light
in direct light conditions. The more areas within the diamond that are
reflecting back light at high angles (75-90 degrees as indicated by the
blacks) causes an increase in the amount of sparkle being returned to
the eye while the former displays stronger and bolder flashes. The comparison is DEFINITELY not that of the pretty vs
the ugly, but a comparison of 2 beautiful diamonds with different
personalities. In suffuse light conditions the first diamond would
have more prominent symmetry which would be observable to the eye while
the 2nd (with skinnier arrows) would be less prominent, yet as GIA
points out there is an even pattern of brightness and dark areas.
This is an important thing to point out because this *contrast* that GIA
is examining is NOT a contrast of light return vs. light leakage (MSU
contrast) but is a contrast of facets reflecting back light vs. facets
reflecting back shadows/colors of things obstructing light (i.e..
lights/darks). The Isee2 analysis is technology that digitally
measures this feature of *brightness* and is a concept we first
introduced in our tutorial on the subject which can be learned more
about here. With regards to the 2 teachings on contrast I have always
personally favored the "light/dark" contrast (Isee2) as opposed to the
"light return/leakage" contrast (MSU/Holloway) as I don't feel a diamond
should be rewarded for leaking more light. I am glad to see GIA
concurs. One more point to note about this particular diamond is
that GIA is not placing any emphasis on the formation of a
"Hearts" pattern (clefts, points or chevrons). They are focusing
on the *face up* position which of course is the most important. Web
sites that place too much emphasis on the "hearts" (only observed
face down) is losing site of what's really important to a diamonds "face
up" appearance. And this is coming from a Hearts & Arrows nut
here. :) |
|
|
Grade 1 - Example 3
- RD20
| Diamond Stats |
Pic 1: MSU Jewelry Store Lighting |
Pic 2: Simulated LightScope Results |
GIA Image RD20 |
Table: 61%
Crown>: 34.5°
Pav>: 40.8°
Stars: 55%
lower gird: 80%
girdle: medium
culet: none
depth: 59.6%
polish: VG
symmetry: VG
|
 |
 |
 |
|
|
|
|
|
|
| Another great example, specifically for those in the
trade who favor the 60/60 combinations (although this diamond does not
have *exactly* a 60% depth with a 60% table, it's darn close). Of
course I'm going to point out that this diamond DOES not receive the top
grade from GIA because of its table/depth combination but primarily
because of the crown/pavilion angle relationship (34.5/40.8) which is
the primary determining feature to determine whether facets will
function as mirrors or windows. So
60/60 diamonds *can* indeed have ideal brilliance but not on
that virtue alone. They must be cut to the proper angles in order
to reflect back light properly. The primary feature to learn about
this particular diamond is how little table size actually contributes to
the (internal) reflective properties of the diamond. I
have a particular fondness of this particular combination of major and
minor facet proportions with the exception of the table size (I like em
around the mid 50's) as this particular combination gives off a nice
balance of brightness, fire and scintillation. Interestingly HCA
results do not concur with this GIA grade as well receiving a mediocre
score of over 2.0. |
|
Final thoughts on Grade 1: There is general debate
about which sets of proportions (primarily among the minor facets)
produce the highest brilliance among those in the trade who feature such
diamonds. The beautiful feature about GIA's system is that they
allow many different combinations as tastes may differ from one person
to the other. Some people prefer fewer broader chunkier flashes of
light while others may prefer more smaller flashes. Grade 1 allows
for *both* and all those that fall in between. What is consistent about the Grade 1 classification
is that the greater majority of all facets must be functioning as
mirrors (as opposed to windows) and that there is a balanced
distribution of lights and darks within the diamond
(contrast). Regarding
current optical grading technologies introduced to our trade
(BrillianceScope & Isee2), each of the 3 diamonds examined in this Grade
1 classification would receive no less than High White Light return,
Very High Colored Light Return and High Scintillation as measured on the GemEx BrillianceScope (excellent results reflecting direct light
appearance) and on the Isee2, high marks for brilliance and scintillation
(excellent results reflecting suffuse light appearance). The Isee2
does not measure Fire (colored light return) but it does grade and
measure optical symmetry which is the only category the example stones
provided by GIA would most likely take a hit on as the Isee2 also grades
the precision to which the diamonds optical symmetry has been cut
(Arrows or face up precision of the pattern of lights/darks). As
you'll see when we're exploring the other cut grade classifications, the MSU Jewelry Store lighting graphic (depicted in 2nd column) reflects the
appearance GIA describes in their analysis which is why I have chosen to
use these graphics in our tutorial. Another clear teaching from
the Grade1 classification is that you do not have to have GIA Ex/Ex
polish & symmetry to get the highest optics and apparently the Grade
1 classification. The dependence of excellent optics based on
proper sets of proportions is something we
have taught for years but now GIA confirms it is the proper sets of
angles that will produce the highest brilliance. For those who
feature precision cut Hearts & Arrows diamonds ... GIA has left you the
opportunity to point out how your product even exceeds their grading
standards as long as your Hearts & Arrows are cut to the proper
proportions. So most technologies agree with GIA's
assessment of Grade 1 classification with the exception of the HCA which
gave 2 out of these 3 stones a score of over 2.0. |
Part 2 - Grade 2
Grade 2 - Example 1
- RD16
|
|
|
Extremely interesting example for this Grade 2.
For those who have studied or kept abreast of our developments regarding
contrast brilliance and the Isee2 technology this diamond takes a hit
for what I would term a combination of angles I consider to be
shallow/shallow (introduced 4th quarter 2004 as opposed to steep/deep as
seen in the next GIA example).
The shallow/shallow combo's (shallow/shallow means that if you couple
certain crown angles with pavilion angles that are too shallow it
produces too much head obstruction or darkness) produce an off balance of
darks/lights with an emphasis on too many darks. GIA comments "the
combination of this particular set of proportions leads to increased
darkness in the pavilion mains". You can observe the results of this by comparing the
brightness image (in column 2) with those in the Grade 1 classification
to see what GIA is talking about. If you're looking at the IS
image and scratching your head, don't be surprised. Red reflector
technology can not (in most circumstances) detect the features that
cause this diamond to get the Grade 2 classification. Hence an HCA
score of less than 2.0 proves ineffective if you are interested in
picking GIA Grade 1 diamonds. This stone scores an amazing .8 on the
HCA which does not correlate with GIA's grade nor from our own testing
of shallow/shallow examples. 2 of these examples which we have
tested can be found at these links (1.10ct
F SI2 &
1.30ct J SI1). So ... if you're working with a company
that does provide IdealScope or HCA scores, bear in mind that these tools alone are
ineffective for selecting Grade 1 diamonds. The only tool we are
aware of at this time to detect these features for *brightness* and
*contrast* digitally is the Isee2.
The LR stereo in MSU software is the lowest grade we've seen so far in
the examples given and contrast is the lowest as well in the 4 examples
given thus far so this is a good indicator. Of grade 2
diamonds, it is these types (the shallow/shallows) that are hardest to
detect via the net and via it's Sarin measurements or most available
online tools (HCA and IdealScope). Expert consultation is required
to help determine these types with further tests (Isee2 &
BrillianceScope). Let's see how the other Grade 2's score. |
|
|
Grade 2 - Example 2
- RD07
|
|
|
This diamond falls into the Grade 2 classification for
more obvious reasons. #1: It's depth falling at 64.1% is the first
red flag (which would make it appear smaller than usual) and #2, the set
of crown/pavilion angles falls into what would be properly termed a
steep/deep combination. It is these combinations that produce the
extraneous leakage you see taking place under the table in the simulated
LightScope image above as indicated by the extremely pale reds & whites. There
are other, less steep/deep combo's that also produce what many would be
considered too much leakage but with shallower angles that I would have
thought would be a better example of a Grade 2 diamond.
Diamonds cut with these extremely long lower girdles (90%!) will
typically have it's optical strengths in way of scintillation/fire but
not brightness/contrast due to the amounts of leakage taking place
within the diamond. The "splintery" effect GIA speaks of can once again
be observed in the MSU Jewelry store graphic in column 2. Of these first 2 examples given for Grade 2 diamonds
the first example above (RD16) would definitely be the more attractive
of the 2 but the reasoning behind giving them both a Grade 2
classification is justified. These first 2 examples also show us
that there will be certain Grade 2's that some may find more appealing
than other Grade 2's. Also of note within this particular diamond
is it's MSU contrast score which gets a whopping 1.20. This
demonstrates the different nature with which MSU is grading contrast as
opposed to the GIA/Isee2 way. This diamond would have less than
desirable *brightness/contrast* due to it's leakage which is why we do
not side with the MSU results for contrast. |
|
|
Grade 2 - Example 3
- RD03
| Diamond Stats |
Pic 1: MSU Jewelry Store Lighting |
Pic 2: Simulated LightScope Results |
GIA Image RD03 |
Table: 63%
Crown >: 32°
Pav >: 41°
Stars: 60%
lower gird: 80%
girdle: med-sl.thck
culet: none
depth: 58.6%
polish: G
symmetry: G |
 |
 |
 |
|
|
| Another diamond that would fall under the shallow/shallow combo due
to the shallow 32 degree crown angles. In this case HCA concurs
with a score of 2.4 while MSU gives it a LightReturn rating comparable to some of the Grade
1 stones. If you take note the pavilion mains (arrows) are notably
darker in the first pic (similar to the first Grade 2 example) except
the arrows are skinnier due to longer lower girdles. This is a
stone that would perform better in direct and ambient light conditions
than it would in suffuse (or white hemisphere lighting). |
|
Final thoughts
on Grade 2: As we enter the Grade 2 classification we
begin to see deviations in crown/pavilion angles that side with either a
steep/deep or shallow/shallow combination of angles. Points of
note to be taken here once again ... red reflectors and HCA scores may
not be the best instruments for pre-determining these grades as diamonds
with IdealScope images similar to the 1st and 3rd examples
(shallow/shallow examples) are typical of stones that would generally
get high recommendations from people recommending stones with these
images/data via the web. The HCA is particularly useful for weeding out
steep/deep combo's but not the shallow/shallows. While we do
consult the results of these tools we do place a heavier emphasis on the
more advanced digital technologies (namely BrillianceScope & Isee2) as
many, even within our own trade do not know how to properly interpret
the results they see from the red reflectors (not to mention the large
variety of graphics that can be generated from these scopes from one
photographer to another on the same stone!). Our advice, if
you want to ensure a Grade 1 classification before the system is
released by GIA, is to pursue a relationship with retailers who are
offering advanced analysis on their stones and/or are familiar with what
stones will constitute the Grade 1 class and the characteristics that
constitute these grades. It would be my educated guess at
this point that as the grades go down we'll continue to see combinations
of angles that are even steeper/deeper or more shallow than the examples
given in Grade 2. |
Part 3 - Grade 3
Grade 3 - Example 1
- RD22
|
|
| While 35.5° may seem to be a crown angle on the
steep side, a pavilion angle of 39.4° is considerably
too shallow for this combo producing the dark pavilion
mains GIA notes and can be observed in the first
graphic. Our experience shows that when you have crown
angles in the mid 35 degree range, pavilion angles
around the 40.4-40.6 produce the brightness necessary to
cause this stone to get a Grade 1 classification. This
first example given here also demonstrates how an
IdealScope/LightScope image
coupled with a seemingly excellent HCA score of 1.8
may not be the best indicators for the layman, even as
we go down to the Grade 3 classification and actually
demonstrates some of the many of the mistakes I personally made with
red reflector technology when I didn't know how to
interpret what it was I was seeing through these
devices. This diamond will generally have a better
appearance in direct light conditions but will suffer in
softer light conditions where contrast/brightness is
best observed. Of all the technologies we work
with, once again, the BrillianceScope and Isee2 appear
to be the best tools for determining the metrics for
this grade so far. |
|
|
Grade 3 - Example 2
- RD11
|
|
| As compared to the steep/deep combo in Grade 2
(Example 2) here's an even worse combination of angles
(as suspected). HCA properly grades this with a
4.6 (although it did give the Grade 2 stone an even
worse score of 5.1) and MSU with .82 & .85 for light
return. Our only disagreement is with the
outstanding 1.10 contrast score via MSU which is
rewarding this diamond with higher contrast for more
leakage. The long lower girdles at 85% (also
similar to Gr2Ex2) contributes to a splintery appearance
making the best attributes of this stone that of fire &
scintillation as observed in direct light conditions.
You can observe the darkness in the upper girdles in
their graphic which is more than likely due to upper
girdle angles being => 44°.
It is good to know that GIA will be taking this into
account as well (how upper girdles impact appearance). |
|
|
Grade 3 - Example
3 - RD06
|
|
| 23° crown angles is the
red flag here which the HCA properly comments on
regarding the likelihood of this diamond chipping. HCA
will not grade stones with crown angles that are too
shallow. FINALLY (except we'd consider this too late in
the game) do we see the results of a stone that's too
shallow with regards to red reflectors as there are too
many blacks under the table contributing to the darkness
that GIA is talking about. As it is with the
other shallow/shallow combo's the IdealScope image is
seemingly excellent and MSU does reward the diamond with
high marks for light return (which it is properly
doing), however since the MSU software does not
differentiate between the lights/darks (for contrast
brilliance) this shows a general strength and weakness
of the Gem Advisor software (at least this version
anyhow). The strength is that the MSU software is
properly showing that this diamonds facets are primarily
functioning as mirrors (as opposed to windows), the
weakness is that this might lead someone to think this
is an excellent diamond when in fact the balance of
contrast stinks (too many reflections of darks and not
enough lights). |
|
|
|
Final thoughts on Grade 3: Grade 3
represents some of the more common crappers that exist on the market
that are generally found in your mall type operations. The 2nd two
examples have obvious red flags even if you were only looking at total
depth info (#2 has a depth of 64.9%, obviously deep while the 3rd
example has a total depth of 57.2%, obviously shallow). The tricky
one is the first example with a normal total depth of 60.6% which is
coupled with a table of 54%. A great example of how foolish
it is to make a decision based on strictly table/total depth alone.
Interestingly, thus far GIA has been giving two shallow/shallow and one
steep/deep in each of their 3 examples within each grade. As stated
earlier the steep/deeps are pretty easy to distinguish and weed out
especially with available online tools like HCA and
IdealScope/LightScope. Perhaps GIA is giving us this 2/1
comparison to emphasize how neglected the metric of brightness is
overlooked by those of us within the trade, especially by gemologists
who incorporate these technologies into their purchasing decisions. It
is also worth noting that there are certain H&A *brands* (not
inexpensive either!) who do charge a premium for their product who cut
their stones to these shallow/shallow combos. It may be worth
reconsidering this metric (and perhaps changing their cutting) if they
are to maintain top optical scores from the most well known lab in the
world. BrillianceScope & Isee2 would accurately determine the
grading here as well. |
Part 4 - Grade 4
Grade 4 - Example 1
- RD19
|
|
|
An extreme shallow/shallow combo for angles. The 54.5% is the initial
red flag here. Both MSU and HCA note the fish eye effect in this
case (which is caused by a reflection of the girdle under the table) and
the HCA is now accurately giving this diamond a hit in
performance as well (despite a seemingly saturated IS image). MSU gives
high marks for light return however the balance of lights/darks is
really poor. Stones this shallow have a more obvious darkness to it than
all previous examples and rightfully gets the Grade 4 classification.
While your rarest diamonds will get the Grade 1 classification, as we
head down the scale here stones getting this bad are sometimes equally
as rare but in the bad sense. :-P |
|
|
|
|
|
Grade 4 - Example 2
- RD33
| Diamond Stats |
Pic 1: MSU Jewelry Store Lighting |
Pic 2: Simulated LightScope Results |
GIA Image RD33 |
Table: 56%
Crown >: 37°
Pav >: 44°
Stars: 55%
Lower girds: 70%
girdle: thin - med
culet: none
depth: 68%
polish: VG
symmetry: VG |
 |
 |
 |
|
|
|
|
Really terrible combo of angles here. HCA fails to grade this due
to the deep pavilion angles and rightfully so. The pavilion is
really deep and evidence of a "nail head" is apparent by the darkness
observed under the table. MSU also shows significantly lower
scores for light return because of the steep/deep combo. The
really short lower girdles (70%) coupled with these angles give the
facets a really chunky look akin to many older cut diamonds on the
market (ie. old european cuts & old mine cuts). |
|
|
|
Grade 4 - Example
3 - RD37
| Diamond Stats |
Pic 1: MSU Jewelry Store Lighting |
Pic 2: Simulated LightScope Results |
GIA Image RD37 |
Table: 70%
Crown >: 33.5°
Pav >: 40.2
Stars: 60%
Lower girds: 80%
girdle: sl.thick-thick
culet: none
depth: 56.9%
polish: G
symmetry: G
|
 |
 |
 |
|
|
|
Oh yes... lack of brightness and scintillation is what characterizes
these shallow combos. A total depth of 56.9% is the initial red
flag. While the stone will have a considerably larger spread than
normal, its coming at the expense of optics (as is the case with all
shallow/shallows). *DEAD* would be one of the best ways to
describe this one. You will be some decent fire in direct light
conditions out of this one but why bother when you can get the best of
all metrics with a Grade 1? |
|
Final thoughts on Grade 4:
More severe angles in way of steep/deeps & shallow/shallows.
Visual performance proceeds to get worse and worse. It appears
that GIA is right on track with their grading system. All three
examples given in the Grade 4 designation have obvious red flags even if
you were just looking at the most basic table/total depth info.
Example 1: 54.5% depth with 62% table.
Example 2: 68% depth with 56% table.
Example 3: 56.9% depth with a 70% table.
Once again they gave us 2 shallow/shallows and 1 steep deep as
examples.
And just when you thought it couldn't get worse...
|
Part 5 - Grade 5
Grade 5 - Example 1
- RD39
| Diamond Stats |
Pic 1: MSU Jewelry Store Lighting |
Pic 2: Simulated LightScope Results |
GIA Image RD39 |
Table: 57%
Crown >: 35.5°
Pav >: 41.2°
Stars: 55%
lower girds: 80%
girdle: ex. thick
culet: none
depth: 74%
polish: G
symmetry: G |
 |
 |
 |
|
|
|
What's interesting about this first example is that GIA has chosen to
use angles & percentages which for the most part are representative of
the current AGS Ideal "0" grading standards with the obvious exception
of total depth (74%!) caused by an extremely thick girdle (and also the
fact that it didn't get the highest marks for polish & symmetry).
The HCA would not grade a stone with a 74% depth so I reduced this to
65% to get a score which in this case accurately weeds out with a score
over 2. All the whites you see under the table in the
LightScope image are indicative of leakage and are a demonstrative
example of the weakness of AGS' current grading system (ie. a proportion
based system as opposed to a performance based system). Excessive
leakage within diamonds such as you see in this example are the causes
for facets appearing darker than they should and this even is less
desirable when it happens under the table. Here is an optical
analysis on a diamond we have scanned in that very closely resembles this
one with the exception of its depth (ours is more shallow with a proper
depth, however the angles are comparable to this example).
http://www.goodoldgold.com/1_23ct_f_vs2_h%26a.htm Our Sarin
measured this diamond with angles of 35.5/41.2 (just like this GIA
example). I can understand this stone getting a Grade 5 classification
primarily because of its depth (which GIA notes) but this set of angles
are less steep/deep than Grade 2 - Example 2 in this tutorial which
would lead me to believe that if the depth of this stone had been more
in the mid 60% range would get a Grade 2 classification instead of a
miserable Grade 5. |
|
|
|
Grade 5 - Example 2
- RD43
|
