-
Please note that a detailed definition of all diamond terms
used is provided in the text below. Please also read the section
of this web-site titled "GIA/AGS
Reports"
Dimonz prices are the lowest anywhere
for finely cut round diamonds with reports from the American
Gem Society (A.G.S.) and the Gemological Institute of America
(G.I.A.), which are largely regarded as the most reliable certificates
by members of the diamond trade. Diamonds with an A.G.S. or
G.I.A. report generally have all of the relevant information
pertaining to the quality of the diamond, including it's cut.
It must be noted that in about the middle
of 2005, A.G.S. revised it's diamond cut grading system.
At about this same time G.I.A. completed a new diamond cut grading
system and, for the first time, started assigning diamonds an
overall cut grade on their diamond grading reports (prior to
2005,
G.I.A. had a diamond grading system but it is different than
the one they currently use and they did not assign an overall
cut grade on their diamond grading reports).
The new cut grading systems for both
A.G.S. and G.I.A. have different criteria than used in their
old systems. For example, in addition to the table, crown angle,
pavillion angle, polish and symmetry ratings previously used
to determine the cut grade of a round brilliant diamond (Class
I to Class IV, as described below), the new G.I.A. system also
includes measurements for the length of star facets and lower
girdle facets and uses a scale from Poor to Excellent to describe
the cut grade. A.G.S. added a measurement for overall light
performance of the diamond to their new reports.
THE OLD A.G.S. IDEAL CUT CRITERIA
VS. THE NEW A.G.S. IDEAL CUT CRITERIA
Diamonds with an AGS "000"
or ideal cut grade under both the old and the new systems
are very optically efficient. However, it is my opinion, that
the criteria used in the new system (i.e., post 2005, as described,
below) is less restrictive than the old one (e.g., under the
new system, diamonds with table percentages of up to 62% can
receive a an "ideal" cut grade-- under the old system
the maximum allowable was 57.5%). I believe that you are
more likely to achieve optimum optical efficiency in your diamond
if you apply the old A.G.S. ideal cut critera (described,
below). Only 1%-2% of all round diamonds meet the old criteria--
a significantly higher percentage of stones meet the new A.G.S.
"ideal" criteria.
THE OLD G.I.A.
CLASS I CUT CRITERIA VS. THE NEW G.I.A. EXCELLENT CUT CRITERIA
G.I.A.'s new cut grading
system does not recognize a single range of measurements (table%,
crown angle, pavilion angle, etc.) for it's Excellent cut
grade (note: Excellent is G.I.A.'s highest rating under
the new system). Rather, based on years of research,
observation andcomputer analysis, G.I.A.'s cut grade reflects
a composite of different combinations of diamond proportions,
polish and symmtery that can produce a very optically efficient
stone. While this is a very reasonable approach, it shoud be
noted a very small percentage of round diamonds meet the old
criteria for a Class I cut grade while a significantly larger
percentage have an Excellent cut grade under the new
system. I believe that you are more likely to achieve optimum
optical efficiency in your diamond if you apply the old G.I.A.
Class I critera (described, below), which is more restrictive
than the new criteria.
BOTTOM LINE:
Under the new cut grading systems, diamonds with an A.G.S. 000
ideal cut grade and those with a G.I.A. Excellent
cut grade are very aesthetic, optically efficicient stones and
are generally guaranteed to be better cut than the vast majority
of round brilliant diamonds. However, if you are looking for
the Creme de la Creme in terms of diamond cut-- it is better
to use the old A.G.S. and G.I.A. systems cut grading systems.
NOTE: It must be noted that old
GIA reports (i.e., those issued before the middle of 2005)
do not contain all of the information necessary to evaluate
cut and does not assign a cut grade. Two crtical pieces
of information not contained in the old G.I.A. reports are the
crown angle and the pavilion angle/depth of the diamond it documents.
Without this information you cannot tell if the diamond is cut
well and whether it represents a good value. All old G.I.A.
certified diamonds sold by Dimonz are accompanied by a Sarin
Brilliant-Eye Report , which provides all of the specific measurements
you need to evaluate the cut of a diamond (including the crown
angle, pavilion angle and pavilion depth) and assigns it a cut
grade using the A.G.S. system (i.e., 0 to 10).
Due
to the large number of requests I have recently received for "ideal cut" diamonds from people researching on the internet,
the following report provides a detailed discussion of Cut,
including a thorough discussion of what is meant by the term
"ideal cut." I apologize for the technical nature of the discussion
which follows. Unfortunately, there is no way of treating this
subject adequately without going into some rather arcane technical
detail.
Of the 4 C's (cut, color, clarity and carat weight), most experienced
gemologists believe that cut is the most important. Why? Because,
in most cases, the cut of the diamond has more impact on it's
brilliance and beauty than the other "C's". From the standpoint
of aesthetics, a beautifully cut diamond of J color and SI1
clarity will put a flawless, D color diamond with an inferior
cut to shame (although the D Flawless diamond may cost 3-4 times
the price of the J S11!!!). The price of diamonds with the same
carat weight, color and clarity may vary in price up to 50%
or more depending on the cut of the stone. The average diamond
sold in the U.S. is poorly cut and lacks the brilliance and
fire that you see in better cut diamonds.
Why
aren't all diamonds cut with "ideal" proportions? The
reason is that diamonds are sold by weight. Consequently, cutters
tend to change the optimum proportions of round diamonds to
retain weight from the rough diamond. The same rough diamond
that produces an "Ideal Cut" 1.20 carat diamond might produce
a poorly cut 1.50 carat diamond by changing the proportions
(e.g., giving the stone a larger table, changing the crown angle,
cutting it too deep, making an extra thick girdle, etc.). The
poorly cut 1.50 carat stone sells for much more than the 1.20
carat "Ideal Cut" stone. Not only is there a .25 carat gain
in weight, the heavier diamond costs more per carat because
the per carat price increases as diamonds increase in weight.
This is why heavier, poorly cut, "dead" looking diamonds, dominate
the domestic diamond market.
In
order to understand the impact of cut on the beauty and value
of the modern round brilliant diamond, it is necessary to understand
many "terms of art" pertaining to cut. You need to be familiar
with all of them if you are to understand what constitutes a
better cut, more brilliant diamond. These include: the Table
Percentage; Crown Angle; Depth Percentage; Pavilion Angle; Pavilion
Depth; Polish; Symmetry; Girdle Thickness; and Culet Size. After
a brief discussion of the A.G.S. and G.I.A. cut grading sytems,
there is a thorough discussion of these terms, what they measure,
and what is meant by "Ideal Cut." Please note that the
vast majority of the diamonds sold in the U.S. Market which
are purported to be "Ideal Cut" diamonds, do not meet
the criteria for this cut classification.
DISCUSSION
OF "IDEAL CUT" DIAMONDS
The
cut grade of a round brilliant diamond is generally based on
how closely it conforms to the "American Ideal Cut".
The Ideal Cut was developed by a mathematician named Tolkowsky
in 1919 (the Ideal Cut is a successor to European Cut and Mine
Cut diamonds but represents a dramatic improvement in optical
efficiency). The purpose of the Ideal Cut was to to produce
the most brilliant diamond possible.
There
are some diamond manufacturers who specialize in fine cut stones
that closely resemble Tolkowsky's model and have excellent cutting
detail. "Super-Ideal" cut diamonds (which cut very closely to
Tolkowsky's original model, and have superior cutting detail)
and "Hearts and Arrows" diamonds ("ideal cuts" which produce
a distinctive hearts and arrows image when viewed through a
special device) are examples, as are diamonds cut by Lazare
Kaplan (a firm specializing in ideal cuts). However, most of
these diamonds are very expensive, costing up to 40% or more
than diamonds available on the open market which are basically
equivalent in terms of optical efficiency.
There
are also many variations of Tolkowsky's ideal cut which employ
the same basic faceting arrangement (i.e., 59 facets) and have
similar proportions, such as the "Eppler Fine Cut"; the"Scandinavian
D.N."; and the "Johnson and Rosch" model (note: this model differs
significantly from Tolkowsky's in it's crown and pavilion angles).
In addition there are specialty cut round stones which generally
have more facets in a different arrangement and are purported
to be more optically efficient than the Tolkowsky's Ideal Cut,
e.g., the "Jubilee Cut" (80 facets), the "King Cut"(86 facets)
, the "Magna Cut"(102 facets), and the "Royal 144" (144 facets).
However, round diamonds with one of these specialty cuts are
generally difficult to find at workable prices and, in my opinion,
do not produce a significant improvement in brilliance over
Tolkowsky's "ideal cut."
Even
in the information age, the "American Ideal Cut" developed by
Tolkowsky over eighty tears ago remains one of the most optically
efficient models for diamonds ever developed. Generally speaking,
it is also the benchmark upon which the cut of all round brilliant
diamonds are currently judged. The measurements of Tolkowsky's
model are as follows:
TOLKOWSKY'S "AMERICAN IDEAL CUT"
Table: 53%
Crown Angle: 34.5 degrees
Pavilion Angle: 40.75
Pavilion Depth: 43.1%
Polish: (Unspecified)
Symmetry: (Unspecified)
Ave. Girdle Thickness: (Unspecified)
Culet Size: (Unspecified)
How
closely must a diamond conform to Tolkowsky's original model
to be considered "ideal"? In America, there are two widely accepted
schools of thought on this issue. The A.G.S.'s cut grade "0"
or "Ideal Cut" and G.I.A.'s "Class I" cut grade, differ in some
respects but are very similar. Each of these systems is dicussed,
below.
--------------------------------------------------------------------------------
A.G.S.'s SYSTEM
This
diamond cut grading system was originally developed by Robert
M. Shipley, known as the "Father of Gemology in America." Mr.
Shipley was the founder of both the American Gem Society and
the Gemological Institute of America. Under this system, the
cut grade of a diamond is graded on a scale from 0 (ideal) to
10 (very poor) based on Table %,Crown Angle, Pavilion Depth,
Pavilion Angle, Polish, Symmetry, Girdle Thickness and Culet
size:
A.G.S.
0 (or 000)- IDEAL CUT
A.G.S. 1 - EXCELLENT
A.G.S. 2 - VERY GOOD
A.G.S. 3/4 - GOOD
A.G.S. 5/6/7 - FAIR
A.G.S. 8/9/10 - POOR
A.G.S.
certificates assign the cut grade of a diamond based on how
much it deviates from the "ideal". Under the A.G.S. system,
the cut grade of the diamond is based on it's lowest
rating. For example, if a diamond has a rating of "5"(Fair)
for the crown angle and a rating "0" or ideal on all of the
other cut elements, the cut grade is "5" or Fair. Likewise,
a diamond with a cut grade of "5" on all of the elements, receives
a cut grade of "5."
In
order to be considered "ideal" cut, a diamond has to receive
a rating of "0" on every element, as defined below. Also defined
below, is the A.G.S. criteria for a cut grade of "1" (i.e.,
"Excellent"):
A.G.S. "0" IDEAL CUT (Note: A.G.S. grades diamonds from
0 to 10 on each factor, with "0" being "ideal"; "5" is the average)
Table: 52.4-57.5%
Crown Angle: 33.7-35.8 degrees
Pavilion Angle: 40.15-41.20 degrees
Pavilion Depth: 42.2-43.8%
Polish/Symmetry: Ideal (A.G.S.)-which is
roughly equivalent to G.I.A.'s Very Good or Excellent*
Ave. Girdle Thickness: Thin, Medium or
Slightly Thick
Culet Size: None, Very Small,Small,Medium
A.G.S. "1" EXCELLENT CUT (i.e., the diamond falls outside
of one or more of the allowable parameters for the "0" or "ideal"
cut grade, described above, and within all of the parameters
for the "1" or "Excellent" cut grade, described below)
Table: 51.4-59.5%
Crown Angle: 32.7- 36.3 degrees
Pavilion Angle: 40.15-41.55
Pavilion Depth: 42.2-44.3%
Polish/Symmetry: Excellent (A.G.S.)-which
is roughly equivalent to G.I.A.'s Good*
Ave. Girdle Thickness:
Thin, Medium, Slightly Thick (but may be
Very Thin at some point on the girdle)
Culet Size: None, Very Small, Small, Medium,
Slightly Large
*Note:
Since G.I.A. and A.G.S. use different scales, this represents
Dimonz' opinion as to the equivalence of G.I.A. and A.G.S. Polish
and Symmetry grades.
You
will generally pay 10-15% more for an A.G.S. "000" Ideal cut
diamond than for a diamond with an excellent or very good cut
grade (i.e., A.G.S. 1-2). Those with cut grades of 3 and below
will generally sell for between 25%-50% or more below the cost
of ideal cut stones.
Summary
of A.G.S. Cut Grade System by Element- 0 (Ideal) to 10 (Very
Poor) :
TABLE
%: (0) 52.4-57.5% ; (1) 57.6-59.5% OR 51.4-52.3%; (2)
59.6-61.5%; (3) 61.6-63.5% OR 50.4-51.3%; (4) 63.6-65.5%; (5)
65.6-67.5% OR 49.4-50.3%; (6) 67.6-69.5%; (7) 69.6-71.5% OR
48.4-49.3% ; (8) 71.6-73.5% OR 47.4-48.3%; (9) 73.6-75.5% OR
46.4-47.3%; (10) 75.6% and greater OR 46.3% and less.
CROWN
ANGLE (in degrees): (0) 33.7-35.8; (1) 32.7-33.6 OR 35.9-36.3;
(2) 32.2-32.6 OR 36.4-36.8; (3) 61.6-63.5% OR 50.4-51.3% ; (4)
31.2-31.6 OR 37.4-37.8; (5) 30.7-31.1 OR 37.9-38.3; (6) 30.2-30.6
OR 38.4-38.8; (7) 29.7-30.1 OR 38.9-39.3; (8) 29.2-29.6 OR 39.4-39.8
(9) 28.4-29.1 (10) 28.3 and less OR 39.9 and greater.
PAVILION
ANGLE (in degrees): (0) 40.15-41.20; (1) 41.30-41.55; (2)
39.80-40.10 OR 41.60-41.85; (4) 39.50-39.75 OR 41.90-42.15;
(5) 39.20-39.40 OR 42.20-42.45; (6) 42.50-42.80; (7) 38.80-39.10
OR 42.85-43.10; (8) 38.30-38.70 OR 43.15-43.55; (9) 43.60-44.10;
(10) 38.25 and less OR 42.20 and greater.
PAVILION
DEPTH %: (0) 42.2-43.8% ; (1) 43.9-44.3%; (2) 41.7-42.1%
OR 44.4-44.8%; (4) 41.2-41.6% OR 44.9-45.3%; (5) 40.7-41.1%
OR 45.4-45.8%; (6) 45.9-46.3% (7) 40.2-40.6% OR 46.4-46.8%;
(8) 39.5-40.1% OR 46.9-47.5% ; (9) 47.6-48.5%; (10) 39.4% and
less OR 48.6% and greater.
POLISH
AND SYMMETRY CHARACTERISTICS: (0) Extremely difficult to
locate under 10 power magnification (10X); (1) Very difficult
to locate under 10X; (2) Difficult to locate under 10X; (3)
Relatively easy to see under 10X; not visible to the unaided
eye; (4) Easy to see under 10X; exremely difficult to see with
the unaided eye; (5) Very easy to see under 10X; very difficult
to see with the unaided eye; (6) Obvious under 10X; difficult
to see with the unaided eye; (7) Relatively easy to see with
the unaided eye; (8) Easy to see with the unaided eye; (9-10)
Obvious to the unaided eye.
GIRDLE
THICKNESS: (0) Thin, Medium or Slightly Thick Average Girdle
Thickness; (1) Very Thin at any point on the girdle; (3) Extremely
Thin and/or Thick at any point on the girdle; (4) Very Thin
Average Girdle Thickness; (5) Very Thick at any point on the
girdle; (7) Extremely Thin Average Girdle Thickness; (10) Extremely
Thick at any point on the girdle.
CULET
SIZE: (0) Pointed/None, Very Small, Small, Medium; (1) Slightly
Large; (3) Large; (5) Very Large; (10) Extremely Large.
--------------------------------------------------------------------------------
G.I.A.'S SYSTEM
In
the G.I.A. cut grading system (a well as the the A.G.S. cut
grading system, defined above), the extremity sets the grade
-- that is, if a single cut characteristic (e.g., crown angle,
table %, polish, symmetry, etc.) falls into a lower category,
the diamond is assigned the cut grade for that category. For
example, if a diamond meets all of the criteria for G.I.A.'s
Class I cut grade but has a 62% table (a Class II characteristic)
the diamond is assigned a Class II cut grade.
It
should be noted that G.I.A. does not include pavilion angle
in assigning the cut grade and relies instead on the pavilion
depth (from which it is possible to closely estimate the pavilion
angle). Also, G.I.A. does not measure culet size in assigning
the cut grade. This is probably because culet size (e.g., None,Very
Small, Small or Medium) is largely irrelevant in evaluating
the cut of a diamond. Only when the culet is Large or Very Large
is it a concern because it may be eye visible, in which case
it is measured as a clarity and characteristic.
CLASS
I (the top cut grade, resembling
the "Ideal Cut"): 53%-60% table; 34-35 degree
crown angle; 43% pavilion depth (that is, the depth of the pavilion
or bottom part of the diamond is 43% of it's width when rounded
to the nearest 1/2%); "Very Good" or "Excellent" Polish and
Symmetry; Medium to Slightltly Thick average girdle thickness
(with no Very Thin, Extremely Thin, Very Thick
or Extremely Thick measurement at any point on the girdle).
You generally pay 15% more for diamonds
with a Class I cut grade than for a similar diamond with a Class
II cut grade.
CLASS
II ("International Fine Trade Cut"): 61%-64% table;
32-34 degree crown angle; 42.0%-42.5% or 43.5%-44.0% pavilion
depth (when rounded to the nearest 1/2%); "Good" Polish and
Symmetry; Thin to Thick average girdle thickness (with
no Very Thin, Extremely Thin, Very Thick or Extremely
Thick measurement at any point on the girdle). These are generally
regarded in the trade as well cut stones. Personally, I will
only buy a Class II diamond with a table of 62% or less. In
my opinion, a 63% or 64% table represents the lower end of this
cut grade and seems to be the point at which you start to observe
a significant reduction of fire. Also, I would not buy a diamond
with an average girdle thickness of "Thick" because they generally
look samller than they should when they are mounted-- i.e.,
they are not very wide because much of the weight of the diamond
is in it's depth (i.e., the girdle).
CLASS
III ("U.S. Domestic Average Cut"; diamonds that have been "stretched" to put them in higher weight categories): 65%-70%
table; 30-32 degree crown angle (when rounded to the nearest
1/2%); 41%-41.5% or 44.5%-46% pavilion depth; "Fair" Polish
and Symmetry; a Very Thin or Very Thick average girdle thickness
(and/or a Very Thin, Extremely Thin, Very Thick
or Extremely Thick measurement at any point on the girdle).
Other measurements may also fall outside of those prescribed
above. These diamonds typically sell
for 10% to 30% less than those with a Class II cut grade.
CLASS
IV: ("Below Average Beauty/Durability) typically discount 30%
to 50% or more from those with a Class II cut grade.
One or more elements fall outside of the parameters defined
for Class III cut, as defined above.
--------------------------------------------------------------------------------
OTHER
VIEWS OF "IDEAL CUT" DIAMONDS
To
further complicate this discussion, there are several other
gemological organizations which have defined their own version
of what constitutes an "ideal cut." For example, an organization
known as the Accredited Gem Appraisers (U.S.A.) has an
excellent system used by most American gem appraisers, which
breaks down each of G.I.A.'s cut grades (Classes I-IV) into
two subclasses, using a formula that is to complex for the lay
person.The International Gemological Institute stipulates
that "Ideal Cut" stones have a 53%-60% table; a 33-36 degree
crown angle; a 42%-44% pavilion depth; a thin to slightly thick
girdle; and a total depth of 58.5%-62.5%. The European Gemological
Laboratory's top cut grade is "Exceptional" and is characterized
by a 54%-57% table; a 34-35 degree crown angle; a 42.5%-43.5%
pavilion depth; and a thin to medium girdle (total depth is
unspecified). The top cut grade recognized by the the Central
Gem Laboratory (C.G.L.) of Japan have a 52%-58% table; a
33-35 degree crown angle; a 42%-44% pavilion depth; a thin to
slightly thick girdle; and a total depth of 59.2%-62.4%. The
requirements for assigning an "Excellent" cut grade specified
by the Association of Gemological Laboratories (A.G.L.)
of Japan are identical to those of the CGL with the exception
of allowable table % (C.G.L. allows for 52%-58% vis a vis 53%-58%
for A.G.L.). The top grade recognized by the Association
of Japan Gem Trust has a 53%-60% table; a 33-35 degree crown
angle; a 43% pavilion depth; a thin to slightly thick girdle;
and a total depth of 59%-63%.
BOTTOM
LINE: So whose definition of ideal cut do we accept? The current
thinking is that both the A.G.S. "Ideal Cut" (as defined above)
and G.I.A. Class I Cut, are considered the norms for the best
cut diamonds available in the market. Diamonds in these cut
categories comprise approximately 1%-3% of the total number
of stones available in the diamond market. For either the A.G.S.
or G.I.A. model, you will pay approximately 10-15% more than
you will for G.I.A.'s Class II (well-made or "International
Fine Trade Cut") diamond (see definition, above).
--------------------------------------------------------------------------------
COMPARISON
OF THE A.G.S. "IDEAL CUT" AND G.I.A.'S CLASS I CUT
Please
note the differences between the A.G.S. "Ideal" and G.I.A.'s
Class I cut parameters. The A.G.S. is stricter in terms of the
acceptable Table percentage for an Ideal Cut diamond, allowing
a maximum of 57.5%, while a G.I.A. Class I cut allows for up
to a 60% table.
G.I.A.
is stricter in terms of the acceptable Crown Angle (which affects
the quality of dispersion or fire in the diamond) and Pavilion
Depth (which determines how much of the light which enters a
diamond is reflected to the eye as "brilliance"). G.I.A. allows
for crown angles from 34-35 degrees while A.G.S. allows from
33.7-35.8 degrees; G.I.A allows for Pavilion Depths of 42.75-43.25%
while A.G.S. allows from 42.2%-43.8%.
Who's
right, A.G.S. or G.I.A.?.... I don't know. Generally speaking,
diamonds with either G.I.A.'s Class I cut or an A.G.S. "0" Ideal
Cut are magnificently brilliant and there don't appear to be
significant differences in light return. The bottom line is
that you'll generally pay 10-15% more for either one than you
will for a stone that is simply "well-cut" (e.g., an A.G.S.
2 or "Very Good" cut grade or a G.I.A. Class II cut).
--------------------------------------------------------------------------------
THE GENUINE IDEAL CUT DIAMOND-- HOW RARE??
The
most complete study of the optical efficiency of round diamonds
was published in the Fall 1998 edition of G.I.A.'s publication,
Gems & Gemology (titled: "Modeling the Appearance of the Round
Brilliant Cut; An Analysis of Brilliance"). One of the interesting
facts pointed out in this study, is that of the 67,621 diamonds
analyzed, only 2,051 or 3% had proportions that fell into the
"ideal" range, which they defined for purposes of this study
as: a 53%-57% table; a 34.0%-34.9% crown angle; and a 42.5%-44%
pavilion depth* which converts to a 40.2-41.3 degree pavilion
angle.
How
many of the 3% of diamonds with ideal proportions meet the other
criteria for an Ideal Cut diamond, i.e. proper girdle thickness
and Very Good to Excellent on Polish and Symmetry grades? We're
probably talking about 1% of available diamonds that meet the "Ideal Cut" criteria.
If
you want to purchase an Ideal Cut diamond, does this mean that
1% of the diamonds in your weight category (e.g. 1 carat, 2
carat, etc.) are worth considering? -- No. In actuality you
may be looking at as few as 1/5th of 1% (one in 500 diamonds
of a particular carat weight) to 1/100th of 1% (one in 10,000)
when you factor in other variables. First of all, you are probably
interested in considering diamonds only in a particular color
and clarity range, e.g., G or H in color and VS2 to SI1 in clarity.
You may also want to eliminate from consideration diamonds that
have strong or very strong fluorescence. Most importantly, you
probably want to eliminate at least 80% of those remaining on
the basis of cost. Remember, because of their scarcity and the
increasing demand for Ideal Cut diamonds, finding a good deal
on one is often very difficult.
*
(Note: these percentages fall outside of the range defined for
G.I.A.'s Class I and the A.G.S. Ideal Cut).
When
you factor in all of these parameters, the ideal cut diamond
you seek usually comprises an infinitesimal portion of the market.
My job is to help you find it at the lowest price available
anywhere!
--------------------------------------------------------------------------------
IMPORTANT
TERMS RELATED TO DIAMOND CUT
In
this section, the terms used in the discussion above, are defined.
Also discussed is how each of the factors, impacts the brilliance
and overall optical efficiency of round brilliant diamonds.
Diagram A
TABLE
PERCENTAGE- This is one of the most important measurements
of the diamond. This is the relative size of the "table" (the
large flat area across the top of the diamond), expressed as
a percentage of the width of the diamond, i.e., the "girdle
diameter" (see Diagram A). For example, if a diamond with a
6.50 millimeter diameter (i.e., the girdle diameter) has a table
measuring 3.90 millimeters across, the table percentage is 60%
(3.9 mm divided by 6.5 mm = 60%). Generally
speaking, the smaller the table, the better the play of light
in the diamond (unless the table is under 52.5%, which is rare).
Generally speaking, well cut diamonds should have a table percentage
of 53%-63%. Most gemological institutions allow for a table
of between 53%-58% for "Ideal Cut" diamonds (e.g., the American
Gem Society specifies a table percentage of 52.5%-57.5%), with
some allowing up to 60% (e.g., G.I.A.'s Class I cut).
Why
are small tables desirable? There are two types of brilliance
which come from a diamond: "life" and "fire" (see diagram B).
The "life" of the diamond is the white light that is reflected
from the table. The "fire" of the diamond is the multicolored
(blue, red, green, orange, yellow and violet), scintillating
light that reflects through the angled part of the crown of
the diamond. The "fire" is regarded as being more beautiful
than the "life" or white light. Stated simply, smaller tables
are desirable because, diamonds with small tables have more
fire and are more aesthetically pleasing than diamonds with
larger tables. However, diamond cutters frequently cut large
tables to save weight from the diamond rough (note: since diamonds
are sold by carat weight, manufacturers generally make more
money this way, although the play of light in the diamond is
negatively affected). You generally pay more for a diamond with
a smaller table because of the greater weight loss from the
rough diamond.
Diagram B
CROWN ANGLE - is the angle formed where the girdle intersects
with the crown (i.e., the top part of the diamond). This angle
forms a sort of prism that changes the white light reflected
from inside the diamond through the crown into the multicolored "fire." If the crown angle is too shallow or too deep, the fire
of the diamond is diminished. The American
Gem Society (A.G.S.) maintains that an "ideal cut" diamond should
have a crown angle of 33.7-35.8 degrees. A Class I cut (G.I.A.'s
top rating) must have a crown angle from 34-35 degrees.
Diagram C
TOTAL DEPTH PERCENTAGE - On a G.I.A. Certificate, this figure
represents the depth of the diamond expressed as a percentage
of it's width. To get the "depth percentage", you take the depth
of the stone in millimeters (the last figure under measurements
on a G.I.A. report) and divide by the diameter (i.e., the Average
Girdle Diameter). Generally speaking,
the Depth Percentage should be between 58.5% and 62.8%. Shallow stones with a depth percentage of less than 58% are
called "spready makes" in the gem trade. They appear to be larger
than normally cut stones of the same weight because they are
wider but they tend to be less brilliant because the pavilion
angle is too shallow and light leakage results (Diagram C, far
right figure). Stones with a depth of over 64% are termed "heavy"
or "deep makes" (Diagram C, middle figure). These stones will
be less brilliant than normally cut stones and may appear to
be dark because much of the light leaks out of the bottom or
pavilion of the stone because the pavilion angle is too steep.
Also called "Nailheads" (because they look dark), these stones
also appear to be smaller than normally cut stones of the same
weight because much of the weight is in the depth of the stone.
Although
the Total Depth Percentage may give a rough idea as to whether
the diamond is too shallow or too deep to play well with light
when the measurements exceed certain parameters (e.g., if it
is under 58% or over 64%), it is too imprecise in determining
the optical efficiency of a stones which fall within the recommended
range. For example, any diamond with a 59%-63% total depth percentage
could be "ideal cut" with a perfect 43% pavilion depth, a 40.8
degree pavilion angle and a 34.5 degree crown angle or it could
just as easily be abominably cut, with a 46% pavilion depth,
a 43 degree pavilion angle and a 29 degree crown angle. For
that matter, it could be the reverse, with a steep crown and
shallow pavilion. Quite frankly, in and of itself, the total
depth percentage of a diamond is usually of negligible value.
In most cases, you must have the pavilion angle and/or pavilion
depth to determine whether or not the stone you are considering
will leak light.
PAVILION
ANGLE (not recorded on the G.I.A. Report) -- This
angle, which correlates directly to the pavilion depth, is the
most important measurement in determining the brilliance of
a diamond. If the pavilion angle is too shallow, the diamond
is less brilliant because of light leakage (Diagram C, above,
far right figure). If the pavilion angle is too steep, you also
get light leakage (Diagram C, above, middle figure). In
conjunction with having a pavilion depth of 42.2%-43.8%, A.G.S.
Maintains that a diamond must have a pavilion angle of 40.15-41.20
degrees to be considered "ideal." Tolkowsky's "American Ideal
Cut" diamond has a pavilion angle of 40.75 degrees. G.I.A.,
to my knowledge, is silent on the issue of the proper pavilion
angle, instead relying solely on the pavilion depth of
the stone in assigning it's cut grades (see discussion, below).
PAVILION
DEPTH PERCENTAGE (not recorded on the G.I.A. Report)
-- This measurement is just another way of expressing the pavilion
angle. It is the distance between the girdle and the culet (point
at the very bottom of the diamond) expressed a a percentage
of the girdle diameter of the diamond. For example, if the distance
between the girdle and the culet is 2.8 mm and the diamond has
a girdle diameter of 6.5 mm, the pavilion depth is 43% (2.8
mm divided by 6.5 mm = .43 or 43%). The pavilion depth, like
the pavilion angle, determines how much of the light which enters
the diamond is reflected back to the eye as brilliance. If the
pavilion depth is too shallow or too deep, the diamond is less
brilliant because less light is reflected back to the eye (see
the middle and far right figures in Diagram C, above, i.e.,
either the light leaks out of the back of the stone or at an
angle where it can't be seen). The A.G.S.
Maintains that the pavilion depth for an "ideal cut" diamond
should be between 42.2%-43.8%. G.I.A.'s Class I cut classification
requires a pavilion depth of 43% when rounded to the nearest
1/2% (i.e., 42.75%-43.25%).
GIRDLE (see Diagram D, below)- This factor measures the thickness of
the "girdle" or the outside circumference of the diamond. There
are typically two measurements given on a G.I.A. Report. The
first measurement reflects the minimum thickness and the second
reflects the maximum thickness for the girdle of the diamond.
If the girdle is the same thickness all the way round, there
will be only one measurement given. The measurements are as
follows: Extremely Thin, Very Thin, Thin, Medium, Slightly Thick,
Thick, Very thick, Extremely Thick.
Diagram D
Do
not buy a diamond that has "extremely thin" as one of the girdle
measurements -- it may be prone to chipping along the girdle.
Don't buy a diamond that has " very thick" or "extremely thick" as one of the girdle measurements-- the cutter has added unnecessary
weight to the diamond which you will pay for! Also don't buy
or those with a single measurement of "thick." Again,
the cutter has added unnecessary weight to the diamond. For
the cut criteria used to evaluate girdle thickness, please refer
to the discussion of the A.G.S. and G.I.A. systems, above.
CULET
(Diagram E) - The culet is a very small facet on the pointed
end of the diamond. The following are
acceptable for all classes of cut, including Class I or "Ideal":
none, very small, small, or medium. Do not buy a
diamond with a large or very large culet. The latter are undesirable
because a large culet may be eye visible through the top of
the stone, appearing as a dark spot or small black hole in the
center of the diamond.
Diagram E
POLISH- This element measures the quality of the finish
on the surface of the diamond, e.g., the presence of abrasions,
polishing lines and other surface characteristics that were
made when the diamond was cut. There are five grades- i.e.,
Poor, Fair, Good, Very Good, Excellent. Any
diamond you consider purchasing should have a polish grade of "Good" or better. Class I or "Ideal" cut diamonds should have
a polish grade of "Very Good" or "Excellent." However,
please be aware that the Polish grade is not nearly as important
as other characteristics (e.g., table percentage, crown angle
and pavilion depth) in determining the optical efficiency of
a diamond. Polish and Symmetry when considered together, comprise
only 1/5 of the cut grade of a diamond.
SYMMETRY-
This element measures the shape and overall cutting detail of
the facets. There are five grades- i.e., Poor, Fair, Good, Very
Good, Excellent. As previously noted,
the symmetry grade in combination with any diamond you consider
purchasing should have a symmetry grade of "Good" or better.
Class I or "Ideal" cut diamonds should have a polish grade of
"Very Good" or "Excellent."
HOW
IMPORTANT ARE EACH OF THESE FACTORS ?
How
important is each of these factors in determining the brilliance
of a diamond? Below, I've done something very unscientific.
Assuming we stay within Class I or Class II cut parameters (as
defined, above) how important is each factor on a scale from
0 to 10 in determining the optical efficiency of a diamond?--
0 = not important at all; 1-3 = moderately important; 4-7 =
important; 8-10 = (critical; extremely important).
Table
Percentage......................6
Crown
Angle.............................8
Pavilion Depth/Angle................10
Girdle/Thickness/Culet/Depth must
be within guidelines described, above
Polish.......................................2
Symmetry................................2
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WHY IS IT SO IMPORTANT TO HAVE A SARIN REPORT IN ADDITION
TO THE G.I.A. REPORT?
Let's
illustrate with an example. You are in the market for an ideal
cut, G VS2 diamond, weighing about one and a half carats. You
think you've found one that sells for 20% lower than any other
one you've seen. The G.I.A. Report for the diamond reads as
follows:
Measurements:
7.42-7.45 X 4.54 mm
Weight: 1.50 carats
Depth: 61.1%
Table: 57%
Girdle: Medium
Culet: None
Polish: Excellent
Symmetry: Excellent
Clarity: G
Color: VS2
Fluorescence: None
Comments: None
Let's
analyze this report. The Measurements are fine for a
diamond weighing 1.50 carats. The Depth falls easily
between 58% and 62.8%. The 57 % Table meets the criteria
for both the A.G.S. Ideal Cut and the G.I.A. Class I cut grade.
It has a medium Girdle thickness, no Culet --
fine so far. It also has Excellent Polish and Symmetry.
There is no Fluorescence and the Comments section
is blank. Why is this "ideal cut" diamond selling so cheap?
The
answer is that this diamond is not ideal cut. In fact it is
cut very poorly. If a Sarin report were available, it would
indicate that the diamond has a shallow crown , producing a
crown angle of 30 degrees (negatively affecting the fire in
the stone). Additionally, the pavilion depth is 46%, i.e., the
pavilion is too deep. This means that most of the light that
enters the diamond falls through the bottom part of the stone
rather than being reflected back to the eye, creating a dark,
lifeless diamond (as in the middle figure in Diagram C, above).
What
looks like a great deal on a Class I or Ideal Cut diamond, is
really a lousy deal on a Class III - Class IV diamond that would
typically sell for about 30% -45% less.
Why
would a diamond be cut this way? Why wouldn't the cutter give
this diamond a Class I or Ideal Cut? The answer is simple. Diamonds
are sold by weight. Cutters lose weight from the diamond rough
when they cut a Class I or Ideal Cut stone. The same rough diamond
that produced this 1.50 carat Class III cut diamond might have
only produced a 1.25 carat Class I cut diamond (which is would
sell for $1,500-$2,000 less).
--------------------------------------------------------------------------------
ONE WAY TO SAVE MONEY ON A FINELY CUT STONE
In
my opinion, one of the best ways to save money and get an extraordinarily
optically efficient diamond, is to buy a diamond which meets
all of the criteria for the A.G.S. Ideal Cut but barely misses
on one or two factors - for example, a diamond which has a 33.5
degree crown angle ( A.G.S. "ideal" is 33.7-35.8 degrees) or
a 57.6%-60% table (A.G.S. "Ideal" is 52.4%-57.5% with G.I.A.
allowing up to 60% for it's Class I cut), and/or receives a
"Good" instead of "Very Good" on Polish or Symmetry. For all
intents and purposes, these diamonds are as optically efficient
as an ideal cut stones but cost less. However, if you are a
purist, it's well worth the money to buy a stone which fully
meets the A.G.S. "Ideal" or G.I.A. Class I cut parameters.
Unlike round diamonds, it is impossible to tell whether fancy
shaped diamonds (i.e., princess cut, radiant cut, marquise,
heart shaped, emerald cut, oval, and pear shape) are well cut
from the G.I.A. report. You must actually see the diamond in
order to determine whether fancy cut diamonds are properly shaped
and that the proportions are correct. Fancy shaped diamonds
that are poorly shaped may trade at up to 50% less than well
made stones of the same color, clarity and carat weight.
Dimonz does not generally list fancy shaped diamonds for sale
on the Internet. However, we will assist you in finding a better
quality fancy shape diamond at a good price. This usually takes
some time (occasionally as long as a month or longer) because
the vast majority of fancy shaped diamonds (90% or more) have
been cut improperly to save weight from the rough (since diamonds
are sold by carat weight, saving weight increases profit). For
example the majority of marquise, pear shapes and ovals usually
have pronounced "bow-ties" or dark, extinguished areas that
reduce the brilliance of the stones (usually caused by the stone
being too deep). Princess cuts tend to be too deep and have
thin crowns. Emerald cut diamonds frequently have "bulged pavilions"
or extra weight added by distorting the shape of the bottom
part of the stone. Heart shapes frequently have uneven lobes.
Some pear shapes look more like a shield than a "tear drop"
(a phenomenon known as "high shoulders and flat head") and many
fancy shapes have improper length-to-width ratios, making them
either too fat or too thin to be aesthetically pleasing.
These are just a few of the many cut problems you are likely
to encounter if you are buying a fancy shape. This is one
area where you need the help of an expert- not a sales clerk
at a jewelry store. Please call me (Bill Bailey) to discuss
how to evaluate the cut of different shapes and/or find out
what I have in inventory (phone # 703-237-6856). You may also
let me know if you want me to conduct a search for your stone.
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GENERAL
RECOMMENDATION: FOR ENGAGEMENT RINGS, BUY DIAMONDS WITH G, H
or I COLOR
Diamonds
are graded on a scale from D (perfectly white) through Z (light
yellow). These letter grades reflect the amount of yellow in
the diamond when the it is viewed through the side, against
a white background , with light that simulates North daylight.
The whiter the diamond (i.e., the less yellow) the more beautiful
and valuable it is. D is perfectly colorless or white and Z
is yellow.
For
an engagement ring, you generally want to select a diamond that
doesn't show any trace of yellow after it is mounted. Round
diamonds from D through I color will appear white when they
are mounted. This begs the question: "If all diamonds graded
'I' or better appear white when mounted, why should I pay more
for a D or E colored diamond than I would for one of I color?"
The
body color of all round diamonds graded D through I look white
when mounted. However, if all else is equal in terms of the
cut of the stones, the whiter diamonds, e.g., the D and E color
stones, will have an aesthetic advantage over those of I color.
Specifically, the brilliance or play of light in the top color
stones may appear somewhat brighter and whiter than those with
a slightly lower color. However, an "ideal" cut H or I colored
diamond that plays beautifully with light, may have a significant
aesthetic advantage over a much more expensive D or E color
diamond that is not as well cut.
I
generally recommend against buying diamonds of D or E color.
If you buy a diamond in this color range, you will pay substantially
more for relatively small differences in appearance. My own
preference is for diamonds of G, H or I in color. G, H and I
color diamonds face up perfectly white when mounted and represent,
in my opinion, the optimum combination of value and aesthetics.
Occasionally, I will carry diamonds of D or E color, but only
when I am able to offer them at an exceptionally good price.
When
mounted, diamonds of J color may show a slight tint but just
as frequently, they look white when they are mounted. Diamonds
of J color need to be evaluated on a case by case basis. Frequently,
diamonds of I or J in color with medium or strong blue fluorescence
will appear one or two colors whiter when mounted than they
actually are. If you want to save money and still have a bright
white looking stone, buying a diamond in this color range with
blue fluorescence is one way to do it.
At
K color and below, diamonds typically show increasing degrees
of yellow, as described below:
The
Gemological Institute of America defines color grades as follows:
| D-F |
Colorless
(appear colorless when mounted) |
| G-J
|
Near
Colorless (G, H and I appear colorless when mounted; J may
be slightly tinted) |
| K-M
|
Faint
Yellow |
| N-R
|
Very
Light Yellow |
| S-Z
|
Light
Yellow* |
| |
*
Diamonds with greater saturation than Z are termed "fancy" colored diamonds. |
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Clarity
is the measure of how "pure" the diamond is. Diamonds contain
many types of inclusions. Very small bits of graphite, olivine,
garnet, or other diamond crystals, are common inclusions in
diamonds. Other kinds of inclusions include feathers (small
cracks which can be contained entirely inside the stone or may,
in some cases, break the surface) or "naturals", i.e., slight
indentations on the girdle or outside perimeter of the diamond.
The clarity grade measures how pronounced or observable these
inclusions are.
GENERAL
RECOMMENDATION: BUY A DIAMOND WITH A VS1, VS2 OR SI1 CLARITY
GRADE (Note: As I've noted elsewhere, I only recommend
buying diamonds with G.I.A. Reports).
DIAMOND
CLARITY GRADES
The Gemological Institute of America recognizes the following
clarity grades (in descending order) :
Flawless
- No inclusions when viewed by a trained expert with 10 power
magnification.
VVS1 and VVS2 - "VVS" stands for "very, very slightly
included". Diamonds graded as VVS1 or VVS2 have extremely small
inclusions that are very difficult for a trained expert to find
with the aid of 10 power magnification.
VS1 - "VS" stands for "very slightly included". VS1 diamonds have
inclusions that are very small and discreet and are somewhat
difficult to find with the aid of ten power magnification, even
for someone with training.
VS2
- VS2 diamonds have very small, discreet inclusions that are
somewhat easy to find when examined with 10 power magnification.
Contains no eye visible inclusions.
SI1 - "SI" stands for "slightly included". SI1 stones have small
inclusions that are easy to see with the aid of 10 power magnification
but are totally "eye clean" , i.e., contains no eye visible
inclusions.
SI2 - SI2 stones have small inclusions that are very easy to see
with the aid of 10 power magnification but are "eye clean",
i.e., contains no eye visible inclusions.
I1 - I stands for "included". I1 stones have inclusions which are
obvious under 10 power magnification and may be eye visible.
I2
and I3 diamonds have large inclusions that are visible to
the naked eye and threaten the beauty and/or durability of the
diamond.
DISCUSSION:
If
you're looking to save a little money on your diamond, here
is where to do it. With the naked eye, even a trained expert
can't tell the difference between a "Flawless" diamond and a
diamond with an "SI1" clarity grade, yet a Flawless diamond
may cost two or three times as much as SI1 diamond of the same
color and carat weight . The inclusions in a properly graded
VS1, VS2 or SI1 diamond are small, even under ten power magnification.
Why pay large sums of money for Flawless or VVS diamonds, when
the differences are fairly arcane and cannot be seen with the
unaided eye?
Truthfully,
I don't see why anyone would pay one cent more for a Flawless
stone than a VS2 or an SI1 stone with a very small, beautiful
crystal that took two to four billion years to form inside the
diamond as it developed a hundred miles deep in the earth's
crust. I actually prefer a diamond with a little crystal or
other inclusions that give it a natural character, as long as
they're not eye visible and they don't affect the beauty or
light transmission in the stone (as they do in I1-I3 graded
stones). My feeling about it is this: diamonds are a natural
mineral that should exhibit some evidence of their geological
formation-- a Flawless diamond is just a faceted piece of carbon.
On
the other hand, you want to avoid stones with large, eye visible
inclusions that affect the beauty and/or durability of the stone,
i.e., those with an I1, I2 or I3 clarity grade. If you're buying
a diamond through the internet, without actually seeing the
stone under a microscope, you should also avoid SI2 stones.
Occasionally, SI2 stones have certain kinds of inclusions that
I consider undesirable-- such as large feathers (a euphemism
for "crack") which break the surface of the stone. Also, some
diamonds at the lower end of range for the SI2 clarity are actually
borderline I1 with inclusions that may be eye visible. The bottom
line is, while certain SI2 diamonds are excellent buys, don't
buy them sight unseen from the "net".
When
buying "emerald-cut" diamonds, you should request a slightly
higher clarity grade than SI1. Emerald cut diamonds are a rectangularly
shaped "step cut" stones. Inclusions in emerald cut stones are
visible to the naked eye at higher clarity grades than those
with a "brilliant cut" (e.g., rounds, pears, marquises, hearts,
etc.). If you are buying an emerald cut diamond, I would recommend
a clarity grade of at least VS2 or better.
Before
you purchase a diamond, I would recommend that you visit a couple
of jewelry stores that carry VS2 or SI1 diamonds with grading
certificates from the Gemological Institute of America (G.I.A.)
. View them under a gemological microscope (do not use a jeweler's
loupe!-- they are too difficult to use effectively without experience).
You will be able to see how small and unobtrusive the inclusions
are in a properly graded VS2 or SI1 diamond.
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The "per carat" price of diamonds increases significantly as the
carat weight goes up. This is primarily because the rough diamonds
needed to cut larger diamonds is much more scarce than the rough
used to produce smaller diamonds. As you go up in carat weight
the rough used to manufacture diamonds becomes scarcer and scarcer.
Round
Diamonds. The chart below demonstrates the per carat increase
in price* of round, G color, VS2 clarity and H color, SI1 clarity
diamonds of various weights:
| Weight
in Carats |
Price
Per Carat GVS2 |
Price
Per Carat HSI1 |
| .30.-.37 |
$2200 |
$1600 |
| .38-.45 |
$2400 |
$1900 |
| .46-.49 |
$2700 |
$2100 |
| .50-.59 |
$3400 |
$2600 |
| .60-.69 |
$3650 |
$2800 |
| .70-.79 |
$4500 |
$3700 |
| .80-.89 |
$4850 |
$4000 |
| .90-.95 |
$5500 |
$4600 |
| .96-.99 |
$6000 |
$5000 |
| 1.00-1.19 |
$6700 |
$5400 |
| 1.20-1.49 |
$7200 |
$5800 |
| 1.50-1.74 |
$8700 |
$6900 |
| 1.75-1.99 |
$9350 |
$7400 |
| 2.00-2.49 |
$10,800 |
$8,000 |
| 2.50-2.99 |
$11, 600 |
$8600 |
Fancy
Shapes (i.e., all shapes other than round), generally sell
for different per carat prices than rounds. This is because
of a number of factors. For some shapes, the rough from which
the diamonds are cut is cheaper than it is for rounds. For some
the weight retention for the rough is greater. Other factors,
such as the amount of labor involved in producing certain cuts
and more irregular demand also affects prices. Below is a comparison
of well cut, 1.00 carat, G color,VS2 diamonds of various shapes:
| 1.00
carat GVS2 |
Price
Per Carat* |
%
Difference from Round |
| Round |
$6700 |
0% |
| Pear-Shape |
$5800 |
-15.5% |
| Marquise |
$5700 |
-17.5% |
| Emerald
Cut |
$5900 |
-13.6% |
| Princess
Cut |
$5800 |
-15.5% |
| Radiant
Cut |
$5800 |
-15.5% |
| Oval |
$6000 |
-11.7% |
| Heart-Shaped |
$5350 |
-25.2% |
*Prices
quoted in this section are based on the Rapaport Diamond Report,
which reflects the New York high, cash wholesale asking price
for reasonably well cut diamonds. The Rapaport prices are normally
somewhat above actual wholesale prices but below average retail
prices. For example, Rapaport prices for one carat G/H VS2/SI1
round diamonds are generally 16-18% above actual wholesale prices
published in "The Guide" by Gemworld, Inc. Many, if not
most, of Dimonz' prices are at or below the actual wholesale
cost published in "The Guide."
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