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GENERAL DISCUSSION REGARDING DIAMOND GRADING REPORTS AND DOSSIERS ISSUED BY THE GEMOLOGICAL INSTITUTE OF AMERICA:

In my opinion, the Gemological Institute of America (G.I.A.) diamond grading reports are the most accurate and reliable that are readily available. I rarely use other reports. However, only about 1%-2% of G.I.A. certified round diamonds with an Excellent cut grade meet my criteria (described below under Cut, Fluorescence and Comments (based on round diamond samples taken from Rapnet.com in October 2014 and other studies pertaining round diamond cut).

As noted in a study conducted by Gemworld International and published in the July/August 2014 edition of the GemGuide (a wholesale pricing guide primarily for jewelry appraisers), 67.6% or 2/3 of all round diamonds in a sample of 117,679 stones, received an Excellent cut grade from G.I.A. (Excellent is G.I.A.'s highest rating for cut). The November/December 2014 edition of the GemGuide states "approximately 75% of the round diamonds that go through the GIA lab, receive an Excellent cut grade." The vast majority of G.I.A. certified diamonds with an Excellent cut grade do not meet Dimonz' criteria, which represent less than 3% of the round diamond market.

Also, it is imortant to note that within the past few years, G.I.A. has established diamond grading laboratories in Bangkok, Gaboronne, Mumbai, Ramat Gan and Tokyo. I have not personally seen diamonds and accompanying Reports/Dossiers from some of these these newer laboratories and do not have first-hand knowledge as to whether or not they are as consistent and reliable as the older diamond grading laboratories such as the Carlsbad (formerly in Santa Monica), Johannesburg, and New York laboratories. The location of the diamond grading laboratory that issued the Report/Dossier is identified at the top of the last page. I have heard very bad reviews from reliable trade sources of the diamond grading at one of the GIA laboratories mentioned.

G.I.A. Reports/Dossiers for Round Brilliant Cut Diamonds--Most of the information you need to evaluate the quality of a round brilliant diamond is contained in a G.I.A. Report/Dossier. Please also read the segment of this website on Cut under the "Four C's".

G.I.A. Reports/Dossiers for Fancy Shape Diamonds In my opinion, G.I.A. Reports/Dossiers for fancy shape diamonds (e.g. cushion cut, princess cut, emerald cut, radiant cut, pear shape, oval, marquise, heart shape, et al) do not contain sufficient information to let you know whether or not the diamond you are considering is of good quality and a good buy from the standpoint of cut. While the color, clarity and carat weight of a fancy shape diamond are described, the diamond grading report doesn't tell you enough about the cut.

For example, marquises, pears, radiants and ovals frequently have pronounced dark spots in the center in the shape of a bow-tie and/or may have an undesirable shape.

--Princess cut diamonds tend to be cut too deep to save weight from the rough (i.e., the total depth percentage is over 73% of the width of the stone) and they have dark, extinguished areas in the center of the stone (sometimes called the X effect because the dark spot in some deep stones freqeuntly looks like an X); they tend to have thin crowns (under 10% of the width of the stone) which negatively affects the play of light; and they look smaller than their weight would indicate when mounted. In other words

-- Pear shapes are often shaped more like shields than the ideal "teardrop" shape (this is known as having "high shoulders and a flat head"). Emerald-cut diamonds tend to be cut too squarish, too deep, with excessively large tables or with bulged pavilions in order to save weight from the rough, creating a dark, smallish looking diamond with an unappealing shape. Many oval and marquise shaped diamonds are cut too wide or fat to retain weight from the rough and have "bulged" or "flat" wings" (i.e., the four arcs that form the outline of the stone are flattened rather than rounded). G.I.A. reports and dossiers for fancy shaped diamonds do not contain the crown height percentage (ie., the height of the crown of the diamond expressed as a percentage of the width of the stone) which is crucial in determining the optical efficiency of the stone. Also, many fancy shaped diamonds fall outside of the preferred length-to-width ratio necessary to optimize the visual appeal of the stone. These are just some of the problems you encounter when buying a fancy shape. In my opinion, very few fancy shape diamonds are even reasonably well cut.

The bottom line is that cannot buy a fancy shape diamond based on the information given in the G.I.A. report. A quote from Rapaport Diamond Report (the diamond trade Bible, regarding wholesale diamond prices):

"Fancy shape diamonds are more complex than round diamonds and much harder to valuate.The quality of cut, proportions and overall shape of the fancy shape diamond all have great impact on price and liquidity. Poorly cut stones may trade at substantial discounts, while well shaped fine cut stones may trade at a premium. There is also a higher degree of availability difficulties in the fancy market and you may pay significantly higher prices for a select fine stone..... It is not advisable to trade diamonds solely on the basis of the grading report. All stones should be examined by an expert. Consumers are cautioned to consult with a reputable jeweler to avoid buying a poorly cut...diamond."

Fancy shaped diamond prices can vary by up to 50% or more, based on cut alone-- they cannot be purchased based on the information given in the G.I.A. report or dossier. Dimonz will help you find a finely cut fancy shape diamond that plays beautifully with light at a great price.

A SUMMARY OF WHAT I LOOK FOR IN A G.I.A. DIAMOND GRADING REPORT OR DOSSIER FOR A ROUND BRILLIANT DIAMOND:

The information presented below deals only with "round brilliant" cut diamonds. The author believes that diamond grading reports do not contain sufficient information for customers to confidently evaluate other shapes.

Color and Clarity: The author believes that the color and clarity ranges specified below represent the best value. However, I would be glad to assist you in finding stones of any color or clarity.

Color: G, H or I (stones above G in color tend to be too expensive with negligible aesthetic advantage for the money spent). J and below may show a yellowish tint, which is to be avoided.

Clarity: VS1, VS2 or some* SI1s.

Generally speaking, if you purchase stones in the VS1-SI1 clarity, you don't pay extra for arcane differences in clarity which have absolutely no impact on the beauty of the stone at the upper end of the clarity range-- i.e., Flawless (Fl), Internally Flawless (IF) and Very, Very Slightly Included (VVS1 and VVS2). In the top clarity grades, you pay for the rarity of these extremely clean stones and not for any aesthetic impact.

Generally speaking, you should also avoid stones at the lower end of the clarity range (SI2, I1, I2 and I3), because these stones may have inclusions that are visible to the naked eye or otherwise affect the beauty or durability of the stone.

Note: The author personally evaluates each stone offered for sale to make sure that the color and clarity are correctly graded and that they represent the middle to upper level of the color/clarity range. Recently, I've rejected several stones in the VS1 to SI1 clarity grades because they have significant clouds that may interfere with the play of light in the stone. The clouds tend to only be visible when the stone is viewed with a gemological microscope which provides illumination from behind the stone and are generally invisible when viewed with a jeweler's loupe where the light source is usually overhead. I also make sure that the stones I sell do not have dark inclusions, regardless of the clarity grade.

Cut, Fluorescence and Comments:

Measurements: If you add the first and second measurements of the diamond (the maximum and minimum widths of the stone) and divide by 2, you should have the Average Girdle Diameter (AGD). A 1.00 carat round brilliant cut diamond should have an AGD of about 6.5 mm; a 1.25 carat round brilliant diamond should have an AGD of about 7.00 mm; and a 1.50 carat round diamond should have an AGD of about 7.4 mm -- measurements may vary-- please see the table, below, for the appropriate AGD for round diamonds of various weights.

Cut Grade: Excellent

Polish: Very Good-Excellent

Symmetry: Very Good-Excellent

Fluorescence: None or Faint Blue

Depth: 59-63% (of the width of the stone)

Pavilion Angle: 40.4-41.2 degrees

Crown Angle: 33.5-35.5 degrees (Note: G.I.A. rounds the crown angle to the nearest 1/2 degree)

Table: 53-58% (of the width of the stone)

Girdle (thickness): Thin; Thin to Medium; Thin to Slightly Thick; Thin to Thick; Medium; Medium to Slightly Thick; Slightly thick; Medium to Thick.

Culet: None, Very Small or Small

Star Facet Length : 50%-55%

Lower Girdle Facet Length: 75%-80%+

Comments/Diamond Plot : No twinning wisps, laser drill holes, etch channels, knots, chips or cavities, or comments noting that the stone has a brown or other color tint.


HOW TO READ A DIAMOND GRADING REPORTS FOR ROUND BRILLIANT CUT DIAMONDS FROM THE GEMOLOGICAL INSTITUTE OF AMERICA:

Each field on G.I.A.'s diamond grading report is explained below:

1. SHAPE AND CUTTING STYLE- As stated, this field describes the shape and cutting style of the diamond (e.g., "round brilliant").

2. MEASUREMENTS - Example-- 6.45 - 6.52MM (min. and max. width)X 3.91 MM (depth).

To avoid buying a stone that appears too small, take an average of the first two measurements, which represent the maximum and minimum width measurements of the diamond (in the example above, 6.48 mm is the average diameter- i.e., 6.45mm+6.52mm divided by 2). The average should be approximately as follows:

  Ave. Approx. Acceptable Range
.50 carat 5.2 mm (5.1mm-5.3mm)
.75 carat 5.9 mm (5.75mm - 6.0mm)
.85 carat 6.2mm (6.05mm-6.3mm)
1.00 carat 6.5mm (6.45mm-6.55mm)
1.25 carats 7.0mm (6.85mm-7.1mm)
1.50 carats 7.4mm (7.3mm-7.5mm)
1.75 carats 7.8mm (7.6mm-7.9mm)
2.00 carats 8.2mm (8.0mm-8.35mm)
2.25 carats 8.6mm (8.45mm-8.75mm)
2.50 carats 9.0mm (8.75mm-9.2mm)

If you have to interpolate between sizes, there is a direct linear relationship. For example, a diamond weighing 1.12 or 1.13 carats should have an Average Girdle Diameter of approximately 6.75 mm (i.e., halfway between 6.5 mm for a 1.00 carat and 7.0 mm for 1.25 carat).

3. WEIGHT- Weight of the diamond in carats. A carat is equal to 1/5 of a gram.

4. COLOR GRADE - Please see discussion under "Color" on this web-site. Generally, I recommend G, H or I color as representing the best value.

5. CLARITY GRADE - Please see discussion under "Clarity" on this web-site. Generally, I recommend VS1, VS2 or (some) SI1* clarity diamonds. I think these represent the best value. You don't want to pay a high price for exceptionally clean stones (Flawless or VVS clarity diamonds) because the high clarity contributes virtually nothing to their beauty. By the same token, you don't want to buy a lower clarity diamond with eye visible inclusions or other characteristics which may noticeably impact the beauty of the stone (SI2 or Imperfect stones--I1, I2 or I3).

*Note: SI1 represents a broad range of clarity. I only select about one in three diamonds with an SI1 clarity grade (those at the top of the range).

6. CUT GRADE - In my opinion, the overall cut grade for round diamond must be Excellent -- in addition, it must meet all of the other criteria described in this section. The Cut Grade reflects both the Proportions of the stone (the table percentage, pavilion angle,crown angle, the length of the lower girdle and star facets) and the Finish (Polish and Symmetry--see #7 and #8, below).

7. FINISH -- Finish is divided into two parts -- Polish and Symmetry (as defined, below).

Some diamond dealers believe that a diamond that has an Excellent Cut Grade and Excellent Polish and Symmetry is better cut than one with an Excellent Cut Grade and Very Good Polish and/or Symmetry. This is not necessarily so. The proportions of the diamond as defined in this discussion (i.e., the table percentage, the crown angle, pavilion angle, the length of the lower girdle and star facets, etc.) are far more important than the Polish and Symmetry grades in determining the optical efficiency and overall cut quality of the stone. In G.I.A. round diamond cut grading classes I took in 1995, the Finish of the stone (i.e., the Polish and Symmetry grades combined) comprised only 20% or 1/5 of the overall cut grade. The Proportions (i.e., the table percentage, crown angle, and pavilion%/angle) comprised 80% or 4/5 of the overall cut grade.

In many cases, a round diamond with an Excellent Cut Grade and Very Good Polish and Symmetry, is much better cut than a stone with an Excellent Cut Grade, and Excellent Polish and Symmetry. For example, a round diamond with an Excellent Cut Grade that has a 53-57% table, a 34.5% crown angle, and a 40.8 degree pavilion angle (as well as the proper length of the lower girdle and star facets, as defined above) and Very Good Polish and Symmetry, is much better cut than one with Excellent grades on all three factors if the stone has a 62% table, a 41.8 degree pavilion angle or a 31.5 degree crown angle.

Bottom Line: 1) insist on an Excellent overall Cut Grade 2) stay within the Proportions parameters I have described above (i.e., table percentage, crown angle, pavilion angle, lower girdle and star facet length) and 3) don't pay much attention to the Polish and Symmetry grades as long as they are Very Good or better.

7a. 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. In my opinion round stones should have a Polish grade of Very Good or Excellent.

7b. 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. In my opinion, stones should have a Symmetry grade of Very Good or Excellent.

8. FLUORESCENCE- G.I.A. assigns one of five levels for this element: None (i.e., no fluorescence), faint, medium, strong, very strong. Generally speaking, ratings of "none" or "faint blue" fluorescence have little or no impact on the value or aesthetic appeal or value of a diamond in the D to I color and VS1 to SI2 clarity range. In most cases, medium, strong or very strong blue fluorescence does not adversely affect the appearance of a diamond. However, a small percentage of strongly fluorescent diamonds appear milky when exposed to strong ultraviolet light. It should also be noted that diamonds with medium, strong or very strong blue fluorescence in the D through H color range in VS and better clarities, generally discount 5%-10% or more from those with faint blue or without fluorescence. When buying diamonds in the J-Z color range, you may pay premiums for stones with blue fluorescence because the blue negates the yellow tint in these diamonds and makes them appear whiter than they actually are.

What is Fluorescence? Diamonds are composed of carbon. They develop approximately 100 miles deep in the earth from a form of carbon called graphite (the same as in pencil lead) which is under tremendous pressure and heat. Sometimes, over a period of hundreds of millions of years, the forming diamond absorbs trace elements of minerals other than carbon. After it is mined, these "absorbed minerals" may cause the diamond to show traces of another color (usually blue) when exposed to ultraviolet light.

The effect of blue fluorescence on the appearance and price of diamonds is one of the most controversial and confusing subjects in the diamond business. A study of fluorescence conducted by G.I.A. And published in the Winter 1997 edition of Gems and Gemology (A Contribution to Understanding the Effects of Blue Fluorescence on the Appearance of Diamonds) states: "(when viewed by experienced observers) In the table up position (as is commonly encountered in jewelry), diamonds described as strongly or very strongly fluorescent were, on average, reported as having a better color appearance than less fluorescent stones. In this study, blue fluorescence was found to have even less effect on transparency. These observations confirm G.I.A. GTL's (Gem Trade Lab's) experience grading millions of diamonds over the decades." Ironically, strongly and very strongly blue fluorescent diamonds in better colors discount even though the effect of fluorescence on the diamond's appearance is generally positive.

Another irony is that in the traditional color grading scale (pre-G.I.A.) the top color grade for diamonds was "Jager" or "Blue-White." This referred to perfect "D" color white diamonds with strong blue fluorescence, which were regarded as a full color grade above "D" color diamonds without fluorescence, because of their beautiful blue-white brilliance. Many years ago you'd pay a premium for a "blue-white." In today's market "blue-whites" discount approximately 10% from D colored stones without fluorescence.

Acceptable Grades for Fluorescence: When buying a better quality diamond of D-I in color and Flawless to SI1 in clarity, I recommend None or Faint Blue fluorescence. In many cases, stones with Medium, Strong or Very Strong Blue fluorescence are also acceptable in terms of appearance but I generally recommend against buying them because they lack liquidity (they are more difficult to sell or trade in for another stone and discount compared to those with faint or no fluorescence).

Diamonds with Fluorescence Other than Blue: As a rule, do not buy diamonds with fluorescence other than blue (e.g., green, orange, et al). Especially, do not buy diamonds with yellow fluorescence. Generally speaking, even very white diamonds may appear yellow if they have yellow fluorescence.

9. COMMENTS & THE DIAMOND PLOT (ON FULL DIAMOND GRADING REPORTS) - Generally avoid stones with twinning wisps (which may interfere with light transmission) and other inclusions which may lower the value and desirability of the stone, such as chips, cavities, knots, or a brown tint. Also avoid stones with laser drill holes (which have been used to remove flaws)--these stones generally sell at a significant discount to unadulterated stones.

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SEVEN IMPORTANT MEASUREMENTS NOTED ON THE IMAGE OF THE STONE DRAWN IN THE G.I.A. REPORT/DOSSIER--

TABLE - This figure represents the table percentage which, like the depth percentage, 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 stone. For example, if a diamond with a 6.50 millimeter diameter (i.e., the Average Girdle Diameter) has a table measuring 3.90 millimeters, 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.

There are two types of brilliance which come from a diamond: life and fire. The "life" of the diamond is the white light that is reflected from the table. The "fire" of the diamond is the multicolored, scintillating light that comes from the diamond. The fire comes from the "crown facets" that surround the table and is regarded as being more beautiful than the "life" or white light.

Smaller tables are desirable because, diamonds with small tables generally 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 rough.

DIAGRAM A

53%-57.5% - Ideal - If all the other factors on the G.I.A. Report are acceptable (e.g. a crown angle of 33.7 to 35.8 degrees; a pavilion depth of 42.2%-43.8%; a pavilion angle of 40.15-41.2 degrees; Very Good or Excellent polish and symmetry; and girdle and culet measurements as defined, below) you will generally pay a premium of 10% to 15% for stones with table percentages in this range, which produce exceptional "fire".

57.6-60% - Superior - If all the other measurements of the diamond are within acceptable parameters, diamonds with tables in this range demonstrate excellent brilliance and fire. Dimonz generally does not sell round diamonds with tables larger than 60%.

Diamonds with tables larger than 60% will have less fire than those with smaller tables.

DEPTH - 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 59% and 63.0%. 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 and crown angles are too shallow and light leakage results (Diagram B, below,far right figure). Stones with a depth of over 64% are termed "heavy" or "deep makes" (Diagram B, middle figure). These stones will be less brilliant than well 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.

DIAGRAM B

PAVILION ANGLE - This angle, which correlates directly to the pavilion depth, is (IMHO) the most important measurement in determining the brilliance of a diamond. If the pavilion angle is too shallow or too steep, the diamond is less brilliant because of light leakage (see Diagram B, above). I generally recommend a pavilion angle of 40.2 to 41.2 degrees.

CROWN ANGLE - This 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. I generally recommend a crown angle of 34 to 35.5 degrees.

GIRDLE -- This factor measures the thickness of the "girdle" or the outside circumference of the diamond. There are typically two measurements given. 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 C

Do not buy a diamond that has "extremely thin" as a girdle measurement -- it may be prone to chipping along the girdle. Don't buy a diamond that has "very thick" or "extremely thick" as a girdle measurement-- the cutter has added unnecessary weight to the diamond which you will pay for! Also don't buy or those have a single measurement of "thick." Again, the cutter has added unnecessary weight to the diamond.

Generally, the following girdle thicknesses are acceptable: Thin; Thin to Medium; Thin to Slightly Thick; Thin to Thick; Medium; Medium to Slightly Thick; Slightly thick; Medium to Thick. Diamonds with Very Thin as one of the measurements may also be acceptable.

CULET- The culet is a very small facet on the pointed end of the diamond (please see Diagram D, below). The following culet sizes are acceptable: none, very small, or small. Do not buy a diamond with a medium, large or very large culet. Medium to very large culets may be visible to the unaided eye through the top of the stone, appearing as a dark spot or small black hole in the center of the diamond.

DIAGRAM D

STAR & LOWER GIRDLE FACET LENGTH - G.I.A. studies have shown that in addition to the pavilion angle, crown angle and table perentage, the length of the star facets and lower girdle facets can have a significant impact on the light return and aesthetics of the stone. The triangular star facets on the crown shoud have a length of 50%-55% (i.e., at least half the distance between the table and the girdle) and the pairs of lower girdle facets should extend from 75%-80% of the distance between the girdle and the culet (please see the Proportions diagram, above).

 

 

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