The 4Cs of Diamond Grading
The 4Cs are four variables that are used to calculate the grade and the value of a diamond: Cut, Color, Clarity, and Carat Weight. Recently Fluorescence has also become a variable in the grading and the value of a diamond.
Cut is the most important "C" of diamond grading. Cut and refers to the proportions, finish, symmetry, and polish, of a diamond and not the shape of the stone. The cut determines the “brilliance” and the "fire" of a diamond and is the most important element in determining a stone’s beauty and value. You can purchase a flawless, colorless diamond and if it’s not "well cut" the stone will look lifeless and dull. You can also buy a SI1 clarity diamond with J color, and if it is cut to the correct proportions, you will have a brilliant stone in spite of the less than perfect grades in both color and clarity. Cut is the first “C” you should consider when buying a diamond, because a stone’s true beauty is determined more by cut and proportion than by color and clarity.
A diamond refracts light just like water, glass, or any transparent medium. An “Ideal Cut” diamond is proportioned so that no matter where light enters the stone, it is redirected out the top. Every surface of a diamond is placed there by a cutter, and the cutter evaluates the stone to achieve the best light return, as well as the best return for their investment. Sometimes a better cut requires a larger amount of the stone to be cut away, and this reduces the diamond’s “carat weight”. Since diamonds are also valued by weight, this creates a dilemma for the cutter in choosing between a quality cut and carat weight. As a result, some diamonds are not cut as well as others because a better cut causes a greater loss in weight. Therefore, you have to consider the quality of the cut, and how it relates to the value of the stone. Well cut diamonds sell at a premium and poorly cut diamonds sell at discounted prices. Cut and proportioning can account for a twenty to a forty percent cost difference between two stones that are otherwise identical. A well cut diamond explodes with dazzling romance, brilliance and fire, and is priced accordingly. This is known as “Flash for Cash”.
Cut and proportioning gained importance in the early 1900s, when a mathematician named Marcel Tolkowsky developed a mathematical model that calculates the behavior of light as it passes through a diamond. He systematically analyzed the optics of the diamond, and he used mathematical formulas to determine the optimum angles that would refract the greatest amount of light back out of the top of the stone. He estimated the best proportions of the “Round Brilliant Cut” so that all of the light entering the diamond followed a controlled path back out. These ideal cut proportions are alternately referred to as the "Tolkowsky Ideal Cut". With minor changes, today's standards for ideal cut diamonds are still based on Tolkowsky's formula. True ideal proportions have only been calculated for round brilliant cut diamonds. Less than ten percent of round brilliant cut diamonds qualify as true ideal cuts, and only about twenty percent qualify as “Preferred Cuts”. This means about eighty percent of diamonds on today’s market are cut for greater carat weight instead of brilliance.
Below are the various numbers that deem a diamond to be an ideal cut diamond. Notice that even the ideal cut has variations. For instance, the table percentage can range from 52.5% to 58.4%. These numbers can vary slightly and the stone will still give an optimum light return.
Round Brilliant "Ideal Cut" Proportions:
A round brilliant cut diamond which has 58 facets is shown below. Since the quality of the cut is directly responsible for the stone's true beauty, the precision with which the facets are arranged is of prime importance. They determine the amount of light reflected back to the eye, called brilliance.
Without "quality cutting” light is lost and not returned to the eye, and the stone will appear to have glassy, watery, or dark areas.
Two important factors of cut proportion grading are “Total Depth Percentage” and “Table Percentage”, and they are usually expressed on grading reports. Measurement of three different parameters allows for easy calculation of these percentages by using the formulas expressed below.
For a round brilliant cut diamond, Total Depth Percentage is calculated as follows:Total Depth (%) = total depth (in mm)
average girdle diameter (in mm)
For a round brilliant cut diamond, Table Percentage is calculated as follows:Table (%) = longest table measurement (in mm)
average girdle diameter (in mm)
Well cut diamonds have a total depth percentage between 58.0% and 63.8%. Diamonds within this range usually provide excellent brilliance. Diamonds that have depths outside this range usually cost much less because brilliance is lost. When the depth percentage is less than 57% or greater than 65%, the center of the diamond appears dark because light is not refracted through the top of the stone.
“Ideal Cut” Proportions for Round Brilliant:
"Premium Cut"
"Tolkowsky Ideal Cut"
"Excellent Ideal Cut"
Total Depth Percentage
58.8% to 63.8%
58.0% to 63.8%
59.2% to 62.4%
Table Percentage
58.0% to 61.0%
53.0% to 58.0%
52.5% to 58.4%
Crown Height
13.0% to 17.0%
14.2% to 16.2%
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Crown Angle
32.7° to 36.3°
33.7° to 35.8°
32.5° to 35.4°
Pavilion Depth
41.7% to 45.0%
42.2% to 43.8%
41.5% to 44.4%
True "Ideal Cut" proportions have only been calculated for the Round Brilliant Cut diamond as they are defined in the table above. Each cut style above represents, in the opinion of its respective designer, the proportions which best balance the brilliance and color dispersion ("fire") within a round brilliant diamond. The table below shows the best or "Preferred Cut” proportions for diamonds of most shapes.
"Preferred Cut" Proportions for Most Shapes:
"Ideal Cut"
Total Depth Percentage
Table Percentage
Round Brilliant 59.2% to 62.4% 52.5% to 61% "Preferred Cut"
Round Brilliant 58% to 63% 53% to 64% Marquise, Oval, and Pear 58% to 66% 56% to 64% Emerald and Radiant 59% to 69% 60% to 69% Princess 60% to 75% 60% to 79% Heart Shape 55% to 65% 51% to 65%
The cut of a diamond can be determined through the use of a standard millimeter gauge, or the Dia-Mension system, a computerized system which takes accurate measurements and proportions of a diamond in seconds.
Remember, the beauty is in the cutting! It is where the cutter truly expresses artistic skill, as the other 3 C's are determined by nature alone...
Color is the second most important “C” of diamond grading. Diamond color usually ranges from colorless (“white”) to yellow with slight tints of gray or brown. “Fancy” colored diamonds can range from intense yellow (“canary”) to various shades of brown (from light “champagne” to “cognac”), and include blue, green, pink and red. Diamonds exist in almost every color of the rainbow, from the very rare red to the sometimes radioactive greens. With exception to the brown shades, some of the “natural fancy colors” are very extraordinary, and can be quite valuable and expensive depending on the color. The champagne colored diamond shows various intensities of brown, and is the most prevalent of fancy colored stones. Since the GIA Color Grade Scale (as shown below) covers tints of yellow and not brown, a new color system named the “C-Scale" (as shown below) was developed to accommodate the champagne and cognac colored diamond. This was primarily due to the opening of Australia’s Argyle Diamond Mine which produces many champagne and brown tinted stones.
"C-Scale" Color Master for Brown Tinted Diamonds:
The D-E-F colors are known as the colorless grades. Grade "D" is reserved for larger diamonds whose colors can be more accurately graded due to their size. Due to the difficulty of grading the color a smaller stones, diamonds less than .50 carats usually receive a top grade of "F".
The G-H-I are known as the "face white" or "face up colorless" because they appear colorless when viewed through the "face up" position, but show a very slight tint of color when viewed upside down. The "brilliance" masks the tint when viewed through the face.
The J-K-L color range offers nice diamonds if they are proportioned properly. A well cut diamond of the J-K-L color range will appear mostly colorless, and can be very cost effective when compared to a diamond of a higher color grade. Remember the "cut" is the key to a beautiful diamond.
GIA Color Grading Scale:
GIA
Color - Commercial Grading
D
E
FColorless
(White)G
H
I
JNear Colorless
(White)K
L
MFaint Yellow
N, O, P, Q, R
Very Light Yellow
S, T, U, V,
W, X, Y, Z
Be aware of "irradiated" diamonds! It is possible to influence the color of a diamond by irradiation followed by heat treatment. This method is not recommended for two reasons. The first is the hazard of exposure to irradiated objects, and the second is the possibility of the color changing over time. Most recently the diamond market has been flooded with low clarity, “irradiated" blue colored diamonds. The Federal Trade Commission requires disclosure of "irradiated" color treated diamonds at the point-of-sale, and I do not deal with "irradiated" diamonds!
The color of the stone can be determined by using a GIA (Gemological Institute of America) Certified set of master stones and/or the Colorimeter, a computer which accurately grades the color of a polished diamond.
Fluorescence refers to the diamond’s ability to fluoresce under ultraviolet (UV) light. Fluorescence is caused by the natural mineral properties of the diamond and is not directly related to a diamond’s color or clarity. Fluorescence in diamonds can be either clear or cloudy (less desirable), and may appear in various colors, but blue and yellow are the most common. A diamond’s fluorescence is usually rated as: Nil or None, Very Faint, Faint, Medium, Strong, or Very Strong. The effect of fluorescence on a diamond’s value depends on its color and its intensity. Usually Nil to Faint fluorescence has very little to no impact. For diamonds of high color grades a “strong” fluorescence gives the stone an oily or milky white appearance, which decreases the stone’s value. In most instances, fluorescence is hardly noticeable and has minimal impact on the diamond's value. Fluorescence often adds value to diamonds of the lower color grades, because it gives the stone a whiter, brighter appearance. It’s not uncommon to find that diamonds with color grades D, E, F, G, and H are lower in price when exhibiting fluorescence and that diamonds with color grades I, J, K, L, M, and N are higher in price when exhibiting fluorescence. Consumers routinely pay more for highly fluorescent diamonds with "I" color grades and below. Generally speaking, the higher the color grade of the diamond the more fluorescence lowers the diamond’s value. Diamonds with cloudy or yellow fluorescence may require even more additional discounts.
A Diamond that Exhibits Strong Fluorescence under Ultraviolet Light:
Diamonds Exhibiting Fluorescence may Fluctuate in Cost:
D to H Colors IF to VS Clarity SI1 to I3 Clarity Very Strong Fluorescence -8% to -12% -3% to 0% Strong Fluorescence -5% to - 7% -1% to 0% Medium Fluorescence -2% to - 4% 0%
I to N Colors IF to VS Clarity SI1 to I3 Clarity Very Strong Fluorescence 0% to +4% 0% to +4% Strong Fluorescence 0% to +4% 0% to +4% Medium Fluorescence 0% to +3% 0% to +3% Slight to Faint 0% to +1% 0%
Clarity is the least important "C" of diamond grading. Clarity describes the clearness or purity of a diamond. This is determined by the number, size, nature, and location of the internal (inclusions) and external (blemishes) imperfections. Since clarity is the easiest grade to demonstrate, many jewelry merchants claim it to be the “most important”. Unfortunately, this could not be further from the truth, and because a lot of merchants commonly resort to quick demonstrations of clarity, it has become the popular “C” with the consumer. Anyone can put a diamond under a jeweler's loupe or microscope to see if it has inclusions, but it takes extensive knowledge and experience to grade the "cut" and the "color" of a diamond.
By definition, any clarity grade of SI2 and above requires magnification to see the inclusion. Since any diamond of SI2 clarity and above is considered "eye clean", why worry about clarity above the SI2 range. You can save a lot of money by buying a diamond that is well cut and proportioned, and with good color, but is in the SI1 or SI2 clarity range. A perfectly cut diamond of D color and SI2 clarity will look the same to the unaided eye as a perfectly cut diamond of D color and VS1 clarity. Of course, if you are told that you are getting a VS1 clarity diamond you want to be certain that you actually are. Diamonds with VS2 clarity and above make for good investments; however, the SI2 diamond could save you hundreds of dollars.
The I2 to SI1 clarity diamonds are the primary stones you should consider for everyday jewelry. Many jewelry merchants only promote the clarity and color grades, and in that order. This is not the proper approach to diamond grading; because a stone’s true value is determined more by cut and proportion than by clarity and color. Cut and proportion should be considered first when buying a diamond. Leave clarity for last because it’s the one area where you can save a lot of money, without giving up true beauty.
GIA Clarity Grading Scale:
Symbol
Meaning
Definition
FL
Flawless
Free from all inclusions or blemishes
IF
Internally Flawless
No inclusions visible at 10x magnification
VVS1
Very Very Slightly Included #1
Inclusions extremely difficult to locate at 10x
VVS2
Very Very Slightly Included #2
Inclusions very difficult to locate at 10x
VS1
Very Slightly Included #1
Minor inclusions difficult to locate at 10x
VS2
Very Slightly Included #2
Minor inclusions somewhat difficult to locate at 10x
SI1
Slightly Included #1
Noticeable inclusions easy to locate at 10x
Sl2
Slightly Included #2
Noticeable inclusions very easy to locate at 10x
I1
Included #1
Obvious inclusions somewhat easy to locate with the unaided eye
I2
Included #2
Obvious inclusions easy to locate with the unaided eye
I3
Included #3
Obvious inclusions very easy to locate with the unaided eye
The above clarity grading scale is in accordance with the GIA (Gemological Institute of America). It is important to note that the GIA Grading system is not static, and has changed slowly over time.
What is SI3? Diamonds graded as SI3 (“slightly included #3") contain clarity characteristics that are very easy to see under 10X magnification. The SI3 category lies between the SI2 and the I1 grade. SI3 was introduced to the diamond trade in 1992 to better serve the changing needs of the marketplace. The following year the Rapaport Diamond Report created an SI3 price column, and the grade has gained wider acceptance over the past decade. While not all labs have adopted SI3, EGL (European Gemological Laboratory) USA began using it on its diamond grading reports in 1997. This step was validated by important global industry organizations that officially recognize the grade, among them are the "World Federation of Diamond Bourses" and the "International Diamond Manufacturers Association".
Be aware of "clarity enhanced" diamonds! Two methods used to enhance the clarity grade of a diamond are “fracture filling” and “laser drilling”. The most common method is fracture filling. A clear glass-like compound is used to fill surface reaching fractures (cracks) within a diamond. This process does not improve the clarity of the diamond, but it definitely improves the appearance of the stone compared to "before enhancement". This process is not stable or permanent, and most major gemological laboratories will not certify fracture-filled diamonds. Most reputable jewelers will not work on jewelry that contains fractured-filled diamonds.
The second method is laser drilling. Laser drilling is used for improving the appearance of diamonds with dark inclusions. A fine laser beam is used to tunnel into the diamond, and to burn-out the existing dark imperfection. Afterwards, acid is then applied to lighten the treated area. This process is considered stable, and all gemological laboratories will grade laser-drilled diamonds. The Federal Trade Commission requires disclosure of “clarity enhanced” (fracture-filled or laser-drilled) diamonds at the point-of-sale, and I do not deal with "clarity enhanced" diamonds!
Carat Weight is the unit of weight for the diamond. A carat is further subdivided in 100 points ( 0.01 carat = l point ). One carat is equal to 0.20 grams. Value per carat increases with carat size, because larger rough diamonds occur less frequently. In other words, 2 half (1/2) carat diamonds taken together will not cost as much as a one (1) carat diamond, as the one carat stone is more rare.
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