The 4 C's
The 4 C's Diamond Grading System: CUT • CLARITY • CARAT WEIGHT • COLOR
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 a stone it will also be critical for you to learn how to read and understand the details of a diamond grading certificate. 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 Quality
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. 5 below), and not how it is faceted.
The Importance of Cut Quality
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.
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 rating system and GIA's new "Cut Grading System".
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 gem 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 pavilion 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.
Poor Diamond Faceting and Symmetry
Due to the mathematics 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.
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.
Balancing Cut and Weight
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.
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.
A Diamond's Spread
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.
FTC Guidelines on Diamond Weight
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.
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.
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.
Diamond Clarity Designations
- 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.
Internal Diamond Inclusions
- Carbon - Tiny black spots caused by carbon inclusions.
- 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 twinning during growth.
External Diamond Inclusions
- 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.
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.
Diamond Color Designations
- 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
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.
Sarin Color Typing
is a relatively new sub-classification of the D through Z grading 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 beneficial to know if your 'F' is a strong 'F,' or a borderline 'G.' Unfortunately, most gem labs do not currently provide color-typing data in their reports and certificates.
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.
Approximately 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.
Skin Tone and Settings
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 combination of other stones, diamonds with a visible tint may be preferred.