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4 C's of Diamonds
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The 4 Cs of Diamonds
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 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 - 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.
Cut Proportions ~ 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:
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.
Poor Diamond
Faceting and Symmetry 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.
The 4 C's of Diamonds: Carat (Weight)
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. CARATBalancing 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. Therefore, 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. 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 therefore, 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. 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. Diamond Clarity Designations
GIA Clarity Grading System The chart in Fig. 4 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.
Fig. 4
Diamond Clarity Grade InflationA 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. Internal Diamond Inclusions
External Diamond Inclusions
The Four Cs of Diamonds - Color
Color is one of the Four Cs representing the four variables that are used to calculate the quality and value of a diamond. 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 yellowier 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
Fig. 1
Fig. 2
Fig. 3
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