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...)
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.