CONTENT: PART I: has
introduced you to the following topics: * Who should read this page and why? *
Short overview of the "4 C's"- the 4 main Characteristics of the diamond gem;
* diamond Shapes & Styles ; * How are diamonds Priced.
Here, in PART II, you are
offered an in-depth study of the "4C's" (diagrams included...)
Here, in PART II, you are offered an in-depth study of the "4C's" (diagrams included...)
Welcome to Van-Daaz's "In-depth" information center.
Proportions and cut determine the brilliance (reflection of light from inside the diamond) scintillation (reflection of light from the surfaces of its facets) and dispersion (colour refraction-the twinkling of colours especially as the diamond is moved about) of a diamond. In the diamond trade, "Cut" (or, "Finish") consists, conventionally, of two separate grading parameters: 'Polish' (usually mentioned first), or, the actual finishing of the different facets' very surface, their very external layer, and, 'Symmetry'. In order to maximize this brilliance, the diamond cutter must place each of the diamond's facets, which act as light-dispersing mirrors, in exact geometric relation to one another. The symmetry of the placement of the facets, the integrity of each facet's borders, its alignment with all other bordering facets, whether or not the table plain is parallel to the girdle plain, whether or not and the extent to which the table or culet are off-center, the levelness (as opposed to waviness) of the girdle and perfect closure of all corners of each facet are contributors to the diamond's over all 'Symmetry' grade. When no such imperfection can be discerned under X10 maginificatyion the symmetry is "Excellent"; If the imperfection is Extremely Hard to discern under X10 times magnification-- the symmetry is graded as "Very Good". If such mishaps are Very Difficult to discern under the same conditions-- the symmetry is graded as Good. We do not promote or sell lower grades ("Fair" and "Poor"). Most diamonds score a Good/Good 'Cut' grading-- Good Polish & Good Symmetry, that is. This type of finish guarantees, due to its demanding criteria ("Very Difficult to descern under X10 time magnificatio...") very satisfactory cut grading, nice overall appearance dispersion & scintillation. On a classic Round Brilliant cut diamond, fifty eight (!) facets must be precisely aligned. Despite the somewhat loose use of the terms "Cut" & "Proportions"--strictly speaking, "Cut" pertains to the"Symmetry" & "Polish" grading (the use of the word "cut", sometimes , in reference to the diamond's shape, as in, e.g., "Radiant Cut" has nothing to do with the "Cut grading"). Proportions are referred to, simply, as "proportions" (rather than "Cut"). Few diamonds are cut to exacting standards since diamond cutters try to maximize their returns on the raw material by leaving the stone as large as possible with minimum waste. As a result, the proportions, symmetry and perfection of the cut and shape may be delegated to play a secondary role. The result is usually a compromise between profit (e.g., size) and beauty (perfection of cut, proportions and shape).
Marcel Tolkowsky is credited with calculating in 1919 the ideal proportions and facet angles that create maximum 'balanced' brilliance, scintillation and fire. Unfortunately the "ideal cut" results in smaller weight yield from the rough diamond crystal and is rarely practiced. Most cutters today slightly compromise Tolkowsky's "ideal cut" in what has come to be known as the "American Brilliant Cut" or "Modern American (brilliant) Cut" (see below). The slightly modified cut still creates impressive results. At the end of 1998, however, a lengthy 6 year meticulous research in the GIA labs yielded some shocking new results (see below).
When the diamond is well proportioned the path of a beam of light is returned directly back to the eye instead of escaping through the bottom or sides of the cut diamond, as a result the diamond will be more lively and brilliant.
A most important criteria of the Cut is the ratio of the depth to its diameter ( i.e. Depth/Diameter whereby the diameter is that of the girdle's--see diagram; In fancy shapes it is the girdle's shortest measurement). In order for the diamond to be considered within the "Ideal" tolerance bracket its depth ratio should be between, approx. 58/100 and 62.9/100 or, "58%" and "62.9%" respectively (see illustration). The measurements are taken in millimeters through the use of a Leveridge Gauge or Micrometer."Table" diameter percentage ( see illustrations for definitions of the names of the different diamond facets ), "Crown" angles and "Girdle" thickness & symmetry are also important. Each of these proportion criteria has its tolerance range. The GIA's 1998 research release points out how detrimental those could also be. These tolerance ranges, loosely speaking, are those manifested in the "American Brilliant Cut". Thus, acceptable table proportion tolerance range for the practical equivalent of the ideal cut ("The Modern American Cut") is larger than the allowed deviation range for its depth: tables are allowed the proportion range of approx. 52% to 59%. The European market, on the other hand, is less preoccupied with Tolkowsky's notion of the 'ideal cut' creating, allegedly, a 'prefect balnce' of brilliance, scintillation and fire as expressed in his, so called, "ideal" cut or, in its "American Brilliant Cut" extension. Europe is distinctively inclined, rather, towards diamonds with Tables between 59% to 66%, as diamonds of these Table proportions look larger to the eye and their brilliance is improved substantially (albeit, admittedly, at some expense of the diamond's scintillation and colour dispersion). Reputable European grading labs such as the HRD or IGI of Antwerp, grade such Table proportions as falling within the "Very Good" category. Similarly, depths ranging from 55% to 63.9% are also considered by the same market and grading labs to be of "Very Good" proportions. Some cutters and dealers promote a 'safe' compromise of a catchy sound--the "60/60" combination (depth of 60% and a table of 60% as well)--taken somewhat flexibly--+/-2, that is...
In fancy cut diamonds (Princess Cut, Emerald, Marquise, Oval, Pear etc.) proportions are measured in relation to the diamond's width--the girdle's cross section narrowest measurement- and tend to be considerably larger (in the high 60's and 70's for squarish shapes). Remember, however, that if they were close to the ideal cut standards--those proportions would be too low in the longer directions of the diamond (unless the culet was sufficiently stretched as well). It is a simple manifestation of the impossibility of "squaring the circle"--what works out for the circular shape simply cannot be fully applied to a square, rectangle or a heart shape...
In girdles, even though girdle thickness of very-thick does not affect a diamond's brilliance it does, however, render the diamond's appearance somewhat smaller as the bulk of its weight is concentrated in the girdle area. The girdle's affect on a diamond's brilliance is negligible. Faceted girdles, however, slightly improve a diamond's brilliance (provided that they have a sufficient number of facets--see below--) as the facets reflect the light back, not allowing, by and large, much of it to escape. Extremely thin girdles, on the other hand, should be avoided due to their fragility in the setting process and after (if exposed).
After 6 years of extensive and intensive research a scientific team of the GIA laboratories published the shocking results of their research into diamond proportions and their effect on diamonds brilliance (the reflection from within the diamond of light falling on and onto its crown). The results were published in the GIA's official publication Gems & Gemology" (Fall 1998 issue). Shorter reviews and discussions appeared in the diamond trade's JCK magazine (January 1999, February 1999) and in the National Jeweler (February 1st.1999). The research paper was co-authored by GIA senior researchers T. Scott Hemphill, Dr. Ilene M. Reinitz, Dr. Mary L. Johnson and Dr. James E. Shigley. While Marcel Tolkowsky based his calculations on a 2-D (two dimensional) model, the GIA team, abled by powerful computers to conduct large number of calculations in short periods of time, has created a 3-D (three dimensional) simulated diamond model capable of tracing light beams path inside the diamond (based on known diamond optical properties--its refractive qualities); The team proceeded to define and measure what they called "WLR" or, Weighted Light Return, a mathematical equivalent, by and large, of a diamond's brilliance. The computer model revealed shocking truths... Thus, after examining more than 20,000 combinations of Table & Depth proportions, Crown and Pavilion angles, as well as actual 67,621 GIA reports on file, the research has established, in its conductors view that--
Similar results have been reached by researchers at Moscow University-- a country known for its excellence in diamond cutting and great mathematicians. You may see those results at the page dedicated to those results--http://www.gemology.ru/cut/ at their site. The page includes also animated illustrations and different diamond proportions modeling and light-ray tracing software!
Arguments, preliminary conclusions and issues:
Admittedly the research did NOT cover scintillation and dispersion. The researchers answer to this accusation is that neither did Tolkowsky take those into consideration in a fully quantified manner (despite the myth...), if only for the most prosaic of reasons--there is not yet a quantifiable, adequate definition of those (the research will try to do exactly that in the coming years). So Tolkowsky too could not measure those and consider them for his final "Ideal Cut" proportions...
Furthermore--The research was based on an idealized, mathematical/geometrical 3-D model, what they refer to as a "virtual diamond", no consideration given to deviation from a perfect symmetry, flawless clarity and complete colorlessness--unlike most commercial diamonds. The researchers answer: Tolkowsky and other inventors of variety of so called "Ideal Cuts" have not taken those into consideration either. Those, incidentally, are also scheduled for future study.
How should these results affect your choices?
Effects on the diamond trade
The trade is still reeling from the publication... Houses that pride themselves of their "Ideal Cut" diamond use every mean to play down the report or flat-out reject it ("what about fire?" "what about symmetry?" "how about checking real-life diamonds and not simulations?"--etc.--but see also answers above...).
Our views?--future new "Ideal Cut" combinartionS are inevitable, termed, more modestly as 'high-brilliance' cuts... for now, the full gamete of 53%-65% seems capable of high brightness... The GIA should review its "less than 30 degrees" 'bad' comment and cutters should experiment more with those..., at the least, try to flirt in their cuts, for now, with just above the GIA crucial 30 degrees 'bad' figure cutting point (e.g., 30-31 degrees)... Ms. Ilene Reinitz, one of the GIA senior researchers involved in the research project and the published paper, admits that the GIA will have soon, upon completion of the project, to revise its educational material, its grading reports and some new instrument development will be required.
Clarity refers to the inclusions and blemishes in the crystal. Gemologists refer to these blemishes, rather, as identifying characteristics avoiding any negative associations and connotations. One must remember that a diamond is a natural substance and any inclusion or pattern of inclusions can be considered as the diamonds unique natural characteristic and "fingerprint". They can also help identify the diamond making your diamond as unique as a snowflake, since no two are exactly alike.
diamonds are graded for clarity according to the number, size, location and type of inclusion. Obviously, less numerous and smaller inclusions that are less centrally located are more desirable than the opposite. Examples of the type of internal inclusions include: "pinpoints", included crystals that are transparent, opaque or carbon . Groups of pinpoints are called "clouds" and fractures are called "feathers". External blemishes include polishing lines, grain lines ( mineral growth twinning planes), scratches, chips, nicks and naturals (part of the rough diamonds original surface or "skin").
As the value of a diamond is determined, partially, by its "purity" or "clarity", standards for measuring the diamond's clarity have been put into place . The clearer the diamond is the rarer and therefore, the more valuable it is . The following terminology is used by the industry.
diamonds in this category are free from internal and external imperfections when examined by skilled professionals under natural or artificial light with a 10X loupe corrected for chromatic and spherical aberration or with a 10X binocular microscope equipped with dark field illumination.
( The following conditions still qualify a diamond as flawless: an extra facet located on the pavilion which cannot be seen from the face-up position; a natural that does not extend beyond the maximum width of the girdle or break the symmetry of the girdle outline and is not seen from the face-up position )
diamonds in this category are free from all internal imperfections (inclusions) but do possess minor surface blemishes. Normally these diamonds may be made flawless by minor repolishing with the exception of surface grain lines.
These grades contain minute inclusions so small or insignificant that they are difficult to locate under 10X loop. When these inclusions are very difficult to locate visible only from the pavilion side or tiny enough to be easily removed by repolishing-the first VVS grade applies. Pinpoints, faint clouds, tiny feathers or bruises characterize the VVS grades.
These grades imply minor inclusions of a size, number and location that stand between those somewhat difficult to observe and those somewhat easier to observe under 10X loop. Small included crystals, small feathers, distinct clouds characterize the VS grades.
These grades contain noticeable inclusions which are easily visible under 10X loop. Normally these inclusions will be centrally located and noticed immediately when the diamond is examined. diamonds in these grades (particularly the SI2 grade) may disclose inclusions to the unaided eye when placed table down on a white background, but not when viewed face-up.
The "Imperfect Categories" contain obvious inclusions when viewed under 10X loop and are visible to the unaided eye in the face-up position. The grades vary from diamonds with inclusions that are difficult to locate by the unaided eye to those with severe inclusions that are easily noticeable.
Though a diamond is said to be "flawless" if no inclusions (internal or external) can be seen under 10 power magnification ( triplet loupe or binocular microscope) truly flawless diamonds are extremely rare.
Clarity Grading Scale
The VS1 category is the cut-off point for what is considered to be a fine clarity grade since the inclusions characteristic of this grade are extremely small and difficult to see at 10X magnification. To the left of the scale from the VS1 grade the differences between each clarity grade are significantly smaller than clarity grades to the right of the VS1 category, where the tolerances for each grade are larger. SI grades are still considered to be very good to good, since their inclusions are not eye visible, especially when examined under normal lighting conditions. Under gemological laboratory conditions where daylight is used the inclusions in the SI2 grade are eye visible when viewed through the back of the diamond (known as the "Pavilion View"). SI grades are considered good choices especially when combined with good color and cut since the cost due to the clarity is usually within popular price ranges and budgets.
Paradoxically enough, the more colorless the diamond, the greater is its rarity and value. Although many diamonds may appear colorless to the untrained eye, the majority contain very slight traces of yellow or brown.
Color quality is critical because a diamond's value increases dramatically the more colorless it is. Color determination consists of comparison with Master-Color diamonds under daylight conditions. A single increase in a diamonds color grade can boost a diamond's value by thousands of dollars depending on the size and clarity grade combinations. diamonds colors are graded from the letter "D" (Colorless) to "Z" (prominent hue).
diamonds are weighed on a carat scale. Trade legend has it that the weight unit's name, "Carat", is derived from the measuring unit of antiquity-the carob fruit seed Keraton in Greek-which seeds are alleged to average 0.2 grams in weight. There are 100 points in one carat. Therefore, weight can also be understood as a ratio ( i.e. points/ 100). A fifty point diamond -half a carat- is then 50/100's of a carat. The size of a diamond measured in millimeters can also assist in determining approximately the diamond's carat weight by using the following formula (not for the novice...): [ Average Diameter in mm. ]2 X [ Depth in mm. ] X 0.0061 (whereby "X" stands for the mathematical operator "times" and 0.0061 is the Size/Weight conversion factor). It is, accordingly, important to understand that there is no direct relationship between perceived size and weight: a fifty point diamond is NOT twice as large to the eye (or as wide) as a twenty five point diamond. It is only twice as heavy and only somewhat larger looking.
It is also important to note that size alone is not enough to determine a diamond's value : One has to consider also the cut and proportions of the diamond, its clarity as well as its color. A large diamond holds little value if it lacks brilliance, purity and good grade color.
A diamond's price is directly related to the combination of the four C's.
A diamond of twice the weight of another is much rarer and therefore more precious and will have a higher price per carat. The price per carat is the monetary value that when multiplied by the diamond's weight (in carats) produces the diamond's price.
Weight also has psychological as well as scarcity value since a diamond of 1 carat or slightly higher is worth more, weight for weight, than a diamond of 0.90 carat because it has reached or exceeded the conventional unit of the complete or full 1 carat. The same principle applies at the dividing line for 2 and 3 carat diamonds etc.-as the price increases in stages with each complete carat. Price jumps for full and numerically "round" "stages" are also applied to diamonds of lesser weights, i.e., a 50 points diamond vs. a 49 points diamond is more valuable weight per weight by being a "full" 1/2 carat.
Color also plays an important role in determining a diamonds value. The price of a diamond varies quite sharply with color. As a rough guide, depending on market conditions, if a diamond with certain characteristics and weight of color "H" were worth 100 units of currency another with the same characteristics of color "F" (two color levels higher) would be worth approximately 130 units, while one with color "J" (two color levels lower) would be worth 80. Moves in clarity grades will affect the price in a similar manner. As the combinations of clarity, cut and color increases in "total score" -- their effect on price becomes greater . However, due to the numerous different possible combinations of Clarity, Color and Cut grading for each Carat weight size the price of each stone is determined through the use of complicated formulas, through tables as well as through reliance on expertise and experience .
A few comments regarding diamond fluorescence are in place for the diamond-curious. Diamonds' fluorescence is their luminescence under light sources that contain UV rays, namely, sunlight and certain artificial lighting. About 47% of all cut diamonds have some traceable level of fluorescence, 99% of which is bluish (few have a yellowish or greenish one).
The property of fluorescence works as follows: under sunlight or any other source of illumination which contains ultra-violet rays, a gem with, e.g., blue fluorescence will emit a bluish 'glow', luminescence or 'halo'. It is considered a real asset in medium and low colour diamonds because the blue glow overcomes and 'cancels' the yellowish natural tint. In higher colours it is a question of personal taste: some frantically look for it because of its unique special effect while others want their diamond absolutely "white" or colourless. Fluorescence, as a rule, under the right (UV rays containing) lighting will render lower colors slightly higher; A diamond with fluorescence will appear as a 'good' example of the same color grade (an 'F' color diamond looking like a 'top' or 'very good' 'F') or, in border line cases, as one color grade higher (a-borderline-'F' case of 'G' will appear to be the same as an actual 'F' under sunlight)!. The authors of this document, personally (as well as a host of our clients), are fond of faint or medium blue fluorescence which adds some 'royal' glow, aura and uniqueness to the diamond, when viewed attentively under sun or UV rays containing, strong lighting. Fluorescent diamonds have traditionally been referred to as Jagers, Premiers, Overblues or just Blue Stones.
GIA repetitive experiments in recent years (1996-8) have shown that, as a matter of course, laymen as well as most experienced professionals could not, at all, discern fluorescing diamonds from non-fluorescing ones (without specialized equipment, that is) while the color-enhancement effect was real (under strong sunlight, in particular under 'northern-light'). Very strong fluorescence (one level above sheere "Strong-Fluorescence"), however, showed, in the minority of cases, occasional, albeit seldom, interference with the scintillation and reflection of the diamond by creating a measure of cloudiness. Accordingly, only and exclusively diamonds with "VERY strong" fluorescence should be checked individually for their clearness, brilliance and overall shine. Very few might justify rejection of these grounds. Otherwise, fluorescence, which is manifested to a degree by most diamonds, should be embraced if not promoted again. Diamonds' "fluorescence" has received a bad wrap following a hasty and poorly researched "investigative report" on South Korean television (at the time--a crucial and substantial diamond market), in the early 1990s, which claimed that buyers were being 'taken-in' by poor quality diamonds, a result, allegedly, of their fluorescence... The cascading and ripple effects of this poorly researched report are still felt today in the diamond trade world-wide, a decade of jewelers training was based on this false premise as well. All, despite the GIA's repeated emphasis in its reports that the claim was absolutely groundless...
"What is and what about the Bow tie Effect"?
Bow Tie Effect (BTE in what follows) is the result of the particular shape of MQ Cut (as well as Oval and other 'fancy' shapes--especially the elongated ones). By being elongated the pavilion angles of the facets along the narrower part of the diamond are steeper than those on the more remote parts of it. Such angles allow light that enters the diamond escape. The escaping light on the narrower parts of the diamond creates a darkish impression that is wider on the circumference of the diamond at those locations and converges to a point in the middle of the diamond. Just like... well, a bow tie shape. It is almost impossible to avoid it altogether as long as the elongated proportions are maintained since the narrower the shape--the steeper is the pavilion at the narrow parts (by getting close to the center, or, Culet of the diamond). Wider shapes might have a lesser BTE. There is no such thing as "acceptable" level of BTE. It is nicer to minimize it but expect, usually, a wider shape (still, not always! elongated shapes may also eliminate the BTE but then it would be at the cost of reduced overall brilliance).
The GIA--Gemological Institute of America-- may be credited with the longest engagement in gemological research of precious stones, and the introduction to the trade of the currently used grading scales. Their grading is considered strict and objective, sought, respected and reputable world wide. Most of the largest diamonds would be sent for GIA grading. Their certificate provides information on the diamond's weight, shape, measurements, total depth percentage, table percentage, girdle type and thickness, culet size, symmetry, polish, clarity, color, fluorescence, general comments and plotting. A new format called "Diamond Dossier" does not include plotting but is accompanied, usually, with laser marking of the report's number on the diamond's girdle for full-proof identification.
The EGL-- European Gemmological Laboratories and the IGI-- the International Gemological Institute-- were, originally Antwerp based only, but are now franchised in the US and other countries. There are two EGL labs in the US: in NY and in LA. Their reputation is somewhat lesser than that of the GIA as they lack the latter's theoretical research track record and are less 'academic' in nature than the GIA. They are smaller in size and in grading volume. While their color grading is largely similar to the GIA's (as they are all based on objective comparison to similar sets of Master Stones), they have been accused, on occasion, of being less strict in their "Clarity" and "Cut" grading. Such accusations, if true, are hardly ever in excess of one grade, if at all. Their service is faster (the EGL boasts a 72 hour guaranteed issue of report) and less costly. Many mid-size to small diamonds are, therefore, graded through them. Their report is more detailed than that of the GIA, providing also the important Crown and Pavilion Height (EGL) and angles (IGI) (so much more important now, in the aftermath of the GIA's published research into those parameters effect on the diamond's brilliance) and an overall grade of proportions (IGI).
The AGS --American Gemological Society-- issues a yet more detailed report than the EGL and IGI, showing also the percentage-height of the Crown, girdle and Pavilion. Like the GIA they are known for their research and laboratory academic activities, they are strict and reputable. Based on the extent of deviation from the proportions of Tolkowsky's cut diamonds are issued grades of AGS-000 through AGS 00, AGS 0, AGS 1 to AGS-5, the former being the closest to Tolkowsky's cut and the latter being the most remote from it...
HRD reports are rarer in the US market as they are issued, still, only in Antwerp by the para-governmental HRD institute-- a research and grading establishment put in place by the Belgian government to provide objective grading and needed reasearch on diamond cutting and marketing. The report is strict and most detailed.
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