The 4 Cs of Diamonds: Cut
The 4 C's Diamond Grading System
More than 100 million diamonds are sold in the United States each year, yet most consumers know very little about the product they are purchasing, and how that product is valued. The '4 Cs' represent the four main variables that are used to calculate the quality and value of a diamond. Both rough and cut diamonds are separated and graded based on these four characteristics.
As a consumer, your first step in shopping for a diamond should be to learn and understand the '4 Cs' diamond grading system. If you are purchasing an expensive stone it will also be critical for you to learn how to read and understand the details of a GIA (Gemological Institute of America) 'Diamond Dossier,' AGL report, or AGS (American Gem Society) 'Diamond Certificate,' or Sarin 'Diamond Grading Report' (see full list of independent testing laboratories, below). You will also want to familiarize yourself with the Federal Trade Commission (FTC) guidelines on jeweler conduct and consumer awareness. This knowledge will help be invaluable when you are comparison shopping for diamonds.
DIAMOND CUT
When jewelers judge the quality of a diamond cut, or "make", they often rate "Cut" as the most important of the "4 Cs." The way a diamond is cut is primarily dependent upon the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, and the popularity of certain shapes. Don't confuse a diamond's "cut" with it's "shape". Shape refers only to the outward appearance of the diamond (Fig. 5below), and not how it is faceted.
When a diamond has a high quality cut (ideal cut), incident light will enter the stone through the table and crown, traveling toward the pavilion where it reflects from one side to the other before bouncing back out of the diamond's table toward the observer's eye (see Fig. 1 below). This phenomenon is referred to as "light return" (Fig. 2 below) which affects a diamond's brightness, brilliance, and dispersion. Any light-leakage caused by poor symmetry and/or cut proportions (off-make) will adversely affect the quality of light return.
The "Shallow Cut" and "Deep Cut" examples in Fig. 1 show how light that enters through the table of a Modern Round Brilliant diamond reaches the pavilion facets and then leaks out from the sides or bottom of the diamond rather than reflecting back to the eye through the table. Less light reflected back to the eye means less "Brilliance". In the "Ideal Cut" example, most of the light entering through the table is reflected back towards the observer from the pavilion facets.
Fig. 1
Keep in mind that the variance in proportions between an "Ideal Cut" (ideal make) and a "Fair, Poor, Shallow or Deep Cut" may be difficult to discern to the novice observer, although there will be a lack of brilliance, scintillation, and fire. Cut quality is divided into several grades listed below.
- Ideal Cut
- Premium Cut
- Very Good / Fine Cut
- Good Cut
- Fair Cut
- Poor Cut
In the past, the "Cut" quality of the "4 Cs" was the most difficult part for a consumer to understand when selecting a good diamond because a GIA or AGS certificate did not show the important measurements influencing cut (i.e. pavilion and crown angle) and did not provide a subjective ranking of how good the cut was. Only a trained eye could see the quality of a good cut. All of that has changed with the AGS Cut Grading system and GIA's new "Cut Grading System".
Fig. 2
The proportion and symmetry of the cuts as well as the quality of the polish are factors in determining the overall quality of the cut. A poorly cut diamond with facets cut just a few degrees from the optimal ratio will result in a stone that lacks gemmy quality because the "brilliance" and "fire" of a diamond largely depends on the angle of the facets in relation to each other. An Ideal Cut or Premium Cut "Round Brilliant" diamond has the following basic proportions according to the AGS:
- Table Size: 53% to 60% of the diameter
- Depth: 58% to 63% of diameter
- Crown Angle: 34 to 35 degrees
- Girdle Thickness: medium to slightly thick
- Facets: 58 (57 if the culet is excluded)
- Polish & Symmetry: very good to excellent
The girdle on a Modern Round Brilliant can have 32, 64, 80, or 96 facets which are not counted in the total number of facets (58). The crown will have 33 facets, and the pavillion will have 25 facets. Other variations of the "Modern Round Brilliant" include the "Ideal Brilliant" which was invented by Johnson and Roesch in 1929, the "Parker Brilliant" invented in 1951, and the "Eulitz Brilliant" invented in 1972.
Due to the mathmatics involved in light refraction, a Round Brilliant cut that does not have the proper proportions and symmetry (off-make) will have noticeably less brilliance. Common cutting problems can occur during the faceting process, when one incorrect facet angle can throw off the symmetry of the entire stone. This can also result in the undesirable creation of extra facets beyond the required 58. The chart below shows several common problems to look for.
Fig. 3
For a Modern Round Brilliant cut (Tolkowsky Brilliant), there is a balance between "brilliance" and "fire". A diamond cut for too much fire will look like cubic zirconia, which gives out much more fire than a real diamond. A well executed round brilliant cut should reflect the maximum amount light from the interior pavilion facets, out through the table, making the diamond appear white when viewed from the top. A cut with inferior proportions will produce a stone that appears dark at the center (due to light leaking out of the pavilion) and in some extreme cases the ring settings may show through the top of the diamond as shadows.
GIA vs AGS Cut Grading
GIA's new cut-grading system is based on averages that are rounded-up to predict 'light performance,' while AGS uses a more exacting combination of proportional facet ratios along with ray-tracing metrics to calculate light return. The "Ideal" designation is an AGS term that is not found on an GIA report. The GIA will give a symmetry demerit for what it calls "non-standard brillianteering" which some manufacturers use to 'improve' on the standardized Tolkowsky-type cuts.
AGS Triple-0 Certification
The American Gem Society (AGS) is the industry leader in laboratory testing of round gems for cut grade and quality. In order for a diamond to receive a "Triple-0" grading, all three categories of cut (Polish, Symetry, Proportion) must meet the "ideal" criteria. A Triple-0 diamond can also be called a "Triple Ideal Cut" or "AGS-Ideal Zero" diamond.
Hearts and Arrows Diamonds
A perfectly proportioned ideal cut that is cut to the exacting specifications of a Tolkowsky Cut,Eppler Cut (European Standard), or a Scan D. N. Cut (Scandinavian Standard) will display a "Hearts and Arrows" pattern when observed through a IdealScope (arrows only), or a H & A Viewer gemscope (FireScope).
Fig. 4
Perfectly formed Hearts and Arrows patterns with eight hearts AND eight arrows (above, left) are only found in diamonds that meet the American Gem Society Laboratories' "0" Ideal Cut specifications. The IdealScope was invented by Kazumi Okuda in the 1970's, and its later incarnation, the "FireScope," was invented by Ken Shigetomi and Kazumi Okuda in 1984. The first official H & A "EightStar" diamond was cut in 1985 by Kioyishi Higuchi for Japanese businessman and FireScope manufacturer, Takanori Tamura.
Fancy Diamond Cuts
The shape of the cut is a matter of personal taste and preference. However, the quality of the cutter's execution of that shape is of primary importance. The shape of the diamond cut is heavily dependent upon the original shape of the rough stone. The round brilliant cut is preferred when the crystal is an octahedron, as two stones could be cut from one crystal. Asymmetrical raw crystals such as macles are usually cut in a "Fancy" style. Several basic diamond shapes (Fig. 5) are listed below.
- Emerald
- Heart
- Marquise
- Oval
- Pear
- Princess
- Radiant
- Round
- Trillion (not shown at diagram)
Fig. 5
Popular fancy cuts include the "Baguette" (bread loaf), "Marquise" or "Navette" (little boat), "Princess" (square outline), "Heart," "Briolette" (a form of Rose cut), and the Pear. The "fancy cuts" are generally not held to the same strict standards as Round Brilliants.
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Independent Diamond Testing Laboratories
Patented Signature Diamond Cuts
Old European Diamond Cuts
Fancy Diamond Cuts
Diamond Cutting
Diamond Chemistry & Composition
The 4 C's of Diamonds: Carat (Weight)
The 4 C's Diamond Grading System
2. Carat
Carat weight is one of the 4 C's, representing the four variables that are used to calculate the quality and value of a diamond. Both rough and cut diamonds are separated and graded based on these four characteristics. As a consumer, your first step in shopping for a diamond should be to learn and understand the "4 C's" diamond grading system.
CARAT
A diamond or gemstone's "Carat" designation is a measurement of both the size and weight of the stone. One "Carat" is a unit of mass that is equal to 0.2 grams (200 milligrams or 3.086 grains) or 0.007 ounce. A carat can also be divided into "points" with one carat being equal to 100 points, and with each point being 2 milligrams in weight. Therefor, a 1/2 carat diamond would be 50 points, a 3/4 carat diamond is 75 points, and a 2 carat diamond is 200 points.
When a single piece of jewelry has multiple stones, the total mass of all diamonds or gemstones is referred to as "Total Carat Weight" or "T.C.W."
The word "Carat" is derived from the Greek word keration, or "seed of the carob". In ancient times, carob seeds were used to counterbalance scales, and as a benchmark weight due to their predictably uniform weight.
Note: Your screen resolution may alter the reproduction size of the chart above. This carat/millimeter sizing chart is meant for comparison purposes only.
Occasionally, a stone cutter will need to make compromises by accepting imperfect proportions and/or symmetry in order to avoid noticeable inclusions, or to preserve the carat rating of the rough stone. Since the per-carat price of diamond is much higher when the stone is over one carat, many one carat diamonds are the result of compromising cut quality to increase carat weight. It is for this reason that an even 1.00 carat diamond may be a poorly cut stone.
Some jewelry experts advise consumers to purchase a .99 carat diamond for its better price, or to buy a 1.10 carat diamond for its better cut. See the chart above for a millimeter to carat size comparison.
Think of the "spread" as the apparent size of a diamond. By sacrificing cut proportions and symmetry, a diamond can have a larger diameter and therefor, a larger apparent "size" for a given carat weight. The spread is the ratio between diameter and three principle geometric components of the crown, girdle and pavilion. A given diamond will have a 'zero spread penalty' if the correct 'ideal cut' symmetry of a 32.5º crown, 40º pavilion, 58% table and 1% girdle are maintained.
According to the Federal Trade Commission's (FTC's) Jewelry Guides on Decimal Representations, "If the diamond's weight is described in decimal parts of a carat, the figure should be accurate to the last decimal place." If the carat weight is shown as ".20 carat" could represent a diamond that weighs between .195 and .204 carat.
If the carat weight is shown as one decimal place, it must be accurate to the second decimal place. A diamond that has a specified carat weight of .5 carats must have an actual weight of between .495 carats and .504 carats.
| Carat Size | | Cost Per Carat (USD) | | Total Cost (USD) | |
|---|
| 0.5 carat | 3,600 | 1,800 |
| 1.0 carat | 6,600 | 6,600 |
| 1.5 carat | 8,500 | 12,750 |
| 2.0 carat | 15,000 | 30,000 |
Diamond prices do not increase in a steady line, as each jump past a even carat weight can mean a significant jump in pricing. The "Rapaport Diamond Report" is a weekly diamond price list based on cut, clarity and weight, that is published by the Rapaport Group of New York.
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Diamond Pricing
Independent Diamond Testing Laboratories
Diamond Chemistry & Composition
Rapaport.com - Rapaport Diamond Report
The Four C's of Diamonds: Clarity
The Four C's Diamond Grading System
Clarity is one of the Four C's, representing the four variables that are used to calculate the quality and value of a diamond. The term "Clarity" refers to the presence or absence of tiny imperfections (inclusions) within the stone, and/or on the surface of the stone. As a consumer, it is important to learn and understand the clarity designations found within the "Four C's" diamond grading system.
CLARITY
All of the grades of diamond clarity shown in the table below, reflect the appearance of inclusions within the stone when viewed from above at 10x magnification Higher magnifications and viewing from other angles are also used during the grading process. In "colorless" diamonds, darker inclusions will tend to create the most significant drop in clarity grade. In fancy-colored diamonds, light or pale inclusions may show greater relief, making them more apparent, causing a greater drop in grade.
- FL - "Flawless" no inclusions at 10 x magnification
- IF - "Internally Flawless" no inclusions at 10 x mag. - small blemishes
- VVS-1 - "Very Very Small" inclusions hard to see at 10 x magnification
- VVS-2 - "Very Very Small" inclusions. VVS1 better than VVS2
- VS-1 - "Very Small" inclusions visible at 10 x mag. - not naked eye
- VS-2 - "Very Small" inclusions VS1 is better grade than VS2
- SI-1 - "Small" or "Slight" Inclusions or "Imperfections" may be "eye clean"
- SI-2 - "Small" or "Slight" Inclusions or "Imperfections" visible to naked eye
- SI-3 - Inclusions large and obvious, little or no brilliance
- I1 to I3 - Imperfect, with large Inclusions, fractures, and flaws
GIA Clarity Grading System
The chart below explains the GIA grading system for inclusions and imperfections. Considerations in grading the clarity of a diamond include the type of stone, point size and the location of inclusions. Inclusions that are near to, or break the surface, may weaken the diamond structurally, therefore reducing its value significantly. On the other hand, it may be possible to hide certain inclusions behind the setting of the diamond (depending on where the inclusion is located), thus minimizing any negative impact of the inclusion.
Diamond Clarity Grade Inflation
A fairly common practice in the jewelry trade is grade-inflation or "grade bumping." According to the Federal Trade Commission's (FTC's) Jewelry Guides, a diamond must be within one clarity grade of its advertised amount at the time of sale. If a jeweler sells a diamond that has an actual grade of VS-1, he or she could legally sell it as a VVS-2.
- Carbon - Tiny black spots caused by undigested carbon inclusions (natts).
- Clouds - Cloudy grouping of tiny pinpoints that may not resolve at 10X Magnification.
- Feathers - Cleavage planes or internal fractures that have the appearance of feathers.
- Grain Center - Concentrated area of crystal growth that appear light or dark.
- Internal Graining - Irregular crystal growth causing internal distortions, waviness, haze.
- Needles - Rutile-like needle inclusions.
- Pinpoints - Minute crystals within the diamond that appear white.
- Pique - Garnet or other Included gem stones
- Twinning Wisps - Inclusions resulting from crystal twining during growth.
- Bearded Girdles - Fine cracks, chips, fringing, or feathers along the outer edge of girdle.
- Bruising - A percussion mark caused by impact.
- Cavities - An indentation resulting from a feather or damage during polishing.
- Chips - Damage usually occurring on the sharp edge of a facet.
- Knots - An inclusion that penetrates the surface, appearing as a raised area.
- Indented Naturals - A natural indentation that was not removed by polishing.
- Filled Fractures - Fractures that have been artificially filled.
- Pits - Dislodged pinpoint inclusions at the surface.
- Surface Graining - Visible surface lines caused by irregular crystallization during formation.
Diamond Fracture Filling
Diamond clarity is sometimes enhanced by filling fractures, much like repairing a crack in your car's windshield. Such diamonds are sometimes called "fracture filled diamonds". According to FTC guidelines, vendors should disclose this enhancement, and reputable filling companies will use filling agents which show an orange or pink flash of color.
There is a significant price discount for fracture-filled diamonds. The GIA will not grade fracture-filled diamonds, in part because the treatment isn't permanent. Reputable companies often provide for repeat treatments if heat causes damage to the filling. The heat generated by a blowtorch used to work on settings can cause damage, therefor it is essential to inform anyone working on a setting if the diamond is fracture-filled, so they can use greater care while working on the piece.
Laser Drilling
Laser drilling involves using a laser to burn a tunnel or hole to a carbon inclusion, followed by acid washing to remove the coloring agent. The drilling process leave tiny telltale shafts or tunnels that are visible under magnification.
The treatment is considered permanent and both the GIA and AGS will issue grades for laser drilled diamonds. The final clarity grade will be the grade that is assigned after treatment. According to Fred Cuellar in his book How to Buy a Diamond, "One out of every three diamonds sold in the United States is laser-drilled."
- Abrasions - Whitish haziness along the junction of facets caused by wear.
- Nicks - Small chips at facet junctions.
- Scratches - Grinding Wheel Marks of scratches from contact with other diamonds.
- Burn Marks - Surface burning from heat buildup during polishing.
"SI-3" is a grade sometimes used in the diamond industry. The designation of SI-3 was popularized by the EGL (European Gemological Laboratory) grading office. Neither the GIA nor the AGS (American Gemological Society), the most reputable well known US labs, assign this grade. Diamonds of this low grade would be inappropriate for jewelry.
Diamond Inclusion Library
Diamond Enhancements & Treatments
Diamond Chemistry & Composition
The Four Cs of Diamonds: Color
The Four Cs Diamond Grading System
Color is one of the Four Cs representing the four variables that are used to calculate the quality and value of a diamond. At present, a Sarin Diamond Color Grading report is the state-of-the-art color measuring standard. As a consumer, it will be beneficial to learn and understand some of the basic parameters for diamond color grading.
COLOR
Most all natural diamonds contain small quantities of nitrogen atoms that displacing the carbon atoms within the crystal's lattice structure. These nitrogen impurities are evenly dispersed throughout the stone, absorbing some of the blue spectrum, thereby making the diamond appear yellow. The higher the amount of nitrogen atoms, the yellower the stone will appear.
In determining the color rating of a diamond, the Gemological Institute of America uses a scale of "D" to "Z" in which "D" is totally colorless and "Z" is yellow. The color chart in Fig. 1 explains the GIA grading system for clear (not fancy-colored) stones.
- D, E, F - colorless (white)
- G, H, I, J - near colorless
- K, L, M - faint yellow or brown
- N, O, P, Q, R - very light yellow or brown
- S, T, U, V, W, X, Y, Z - light yellow or brown
Fig. 1
Due to a diamond's high brilliance, and dispersion of light (fire) when looking through the table or crown, color grading should be determined by examining the stone through the side of the pavilion (Fig. 2), and not by looking at the top of the stone, as in our Fig. 3 example below. Color grading by 'visual-observation is performed against a Master CZ Colored Grading Set.
Fig. 2
Sarin Color Typing
is a relatively new sub-classification of the D through Z gading scale. Each classification is divided into five sub-classifications (D1, D2, D3, D4, and D5). Using a Sarin Diamond Colorimeter DC3000 (aka Gran Colorimeter), jewelers and gem labs can accurately provide a 'color typing' printout of a diamond's color grading that is compatible with AGS, GIA-GEM, IGI, and HRD grading scales. For the consumer, it is extremely benificial to know if your 'F' is a strong 'F,' or a borderline 'G.' Unfortunatly, most gem labs do not currently provide color-typing data in their reports and certificates.
Fig. 3
Golconda Diamonds
Type IIa diamonds (aka Golconda Diamonds) are colorless stones containing negligible amounts nitrogen or boron impurities to absorb the blue end of the color spectrum. These colorless stones, sometimes referred to as "white diamonds," "whiter than white," or "D+," are named after the famous Golconda Diamond Mines located in the state of Hyderabad, India.
D-Flawless - The Holy Grail
Large D-flawless diamonds (those weighing more than 2 carats) are some of the rarest minerals on earth. Only around 600 D-flawless roughs are cut into gems weighing between 1 and 2 carats during a given year, according to the GIA. Even with microscopic inclusions, fewer than 5,000 D-color diamonds weighing over half a carat are found each year.
Diamond Fluorescence
Approximatly 1/3 (35%) of all diamonds have a tendency to fluoresce when exposed to ultra-violet (UV) light. When diamonds are viewed under a UV light-source, they tend to fluoresce as blue. This fluorescent effect can be beneficial to a diamond that has a yellow tint, as the blue fluorescence will cancel out some of the yellow, making the diamond appear "colorless," but the diamond will have a dull, murky appearance when compared to a non-fluorescing diamond. Ultra-violet light is a component of natural sunlight and artificial 4800k to 5000k color-proofing light, so this effect will be more apparent under natural daylight than under artificial incandescent light. See Color in Gemstones for more information.
For diamonds with a color grading of D through H (colorless), fluorescence can negatively impact the value of the stone by 3% to 20%. On the other hand, diamonds with a poorer color grading (I through K), fluorescence could increase the value by 0% to 2% buy improving the color (or lack thereof). Fluorescence is graded as none, faint, medium, and strong.
While some may prefer a very transparent D to F range, others may prefer a "warmer" color found in a G to J range to compliment their skin tone. In some settings with various combinations of other stones, diamonds with a visible tint may be preffered.
Fancy Colored Diamonds
Diamond Enhancements & Treatments
Colored Gemstone Grading Certificates & Reports
Diamond Chemistry & Composition
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