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Diamond Information
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Composition and color
 
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 Type I diamond has nitrogen atoms as the main impurity. If they are in clusters they do not affect the diamond's color (Type Ia). If dispersed throughout the crystal they give the stone a yellow tint (Type Ib), the Cape series. Typically a natural diamond crystal contains both Type Ia and Type Ib material. Synthetic diamond containing nitrogen is Type Ib.
 
 Type II diamond has very few nitrogen impurities. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation. Type IIb is the blue diamond containing scattered boron within the crystal matrix.
 
Diamonds occur in a variety of colors—steel, white, blue, yellow, orange, red, green, pink, brown, and black. Colored diamonds contain impurities or structural defects that cause the coloration, whilst theoretically, pure diamonds would be transparent and colorless.
 
In the late 18th century, diamonds were demonstrated to be made of carbon by the rather expensive experiment of igniting a diamond (by means of a burning-glass) in an oxygen atmosphere and showing that carbonic acid gas (carbon dioxide) was the product of the combustion. The fact that diamonds are combustible bears further examination because it is related to an interesting fact about diamonds. Diamonds are carbon crystals that form deep within the Earth under high temperatures and extreme pressures. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (dH = -2 kJ / mol). Diamonds had previously been shown to burn during Roman times.
 
So, despite De Beers' 1948 ad campaign, diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions.
 
The diamond industry
 
 

Only diamonds are hard enough to cut other diamonds. Polishing and mounting add further value, brilliance, and appeal as jewelry.

 
Due to their high dispersion and unsurpassed hardness, diamonds have long been prized as a constituent of jewellery. A large trade in gem-grade diamonds exists, mostly controlled by the De Beers company, which has used its monopoly to manipulate prices. Unlike precious metals such as gold or platinum, there is a substantial mark-up in the sale of diamonds and there is not a very active market for resale of diamonds, making them rather unsuitable as investments or as a store of value.
 
At one time it was thought over 80% of the world's rough diamonds passed through the Diamond Trading Company (DTC, a subsidiary of De Beers) in London, but presently the figure is estimated at c. 60%. In the late '90s, Canadian prospectors discovered several rich sources of diamonds. For example, the Ekati Diamond Mine, which was opened in 1998, produces 3 million carats (600 kg) of rough diamond every year. The Diavik Diamond Mine was opened in 2004.
 
Diamonds are valued according to the four C's of diamond grading, namely cut, clarity, color, and carat. Both rough and cut diamonds are graded and separated based on these four characteristics at a number of heavily guarded grading centers, such as the DTC.
 
Cut
The history of diamond cutting can be traced to the late Middle Ages, before which time diamonds were enjoyed in their natural octahedral state. The first "improvements" on nature's design involved a polishing of the crystal faces—this was called the point cut. Later still, a little less than one half of the crystal would be sawn off, creating the table cut. Neither of these early cuts would reveal what diamond is prized for today; its strong dispersion or fire. At the time, diamond was valued chiefly for its brilliant lustre and superlative hardness; a table-cut diamond would appear black to the eye, as they do in paintings of the era.
In 1375, there was a guild of diamond polishers at Nürnberg.

In or around 1476 Lodewyk (Louis) van Berquem, a Flemish polisher of Bruges, introduced absolute symmetry in the disposition of facets. He cut stones in the shape known as pendeloque or briolette.

About the middle of the sixteenth century, the rose or rosette was introduced.

The brilliant cut was introduced in the middle of the seventeenth century. The first brilliants were known as Mazarins. They had 17 facets on the crown (upper half). They are called double-cut brilliants.

Vincent Peruzzi, a Venetian polisher, increased the number of crown facets from 17 to 33 (triple-cut brilliants), thereby increasing very much the fire and brilliancy of the cut gem, which were already in the double-cut brilliant incomparably better than in the rose. Yet diamonds of that cut, when seen nowadays, seem exceedingly dull compared to modern-cut ones

Light dispersion from an ideal cut diamond simulant. Notice the near-perfect symmetry of the light reflected out of the stone.
Roughly 1900, the development of diamond saws and good jewellery lathes enabled the development of modern diamond cuts, chief among them the round brilliant cut. In 1919, Marcel Tolkowsky analyzed this cut. His calculations took both brilliance (the amount of white light reflected) and fire into consideration, creating a delicate balance between the two. His geometric calculations can be found in his book on Diamond Design (http://www.folds.net/diamond/index.html).
 
The modern round brilliant consists of 58 facets (or 57 if the culet is excluded); 33 on the crown (the top half above the middle or girdle of the stone) and 25 on the pavilion (the lower half below the girdle). In recent decades, most girdles are faceted. Many girdles have 32, 64, 80, or 96 facets; these facets are not counted in the total. While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.) are not universally agreed upon. One may speak of the American cut or the Scandinavian standard (Scan. D.N.), to give but two examples.
 
Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to.
 
Popular fancy cuts include the baguette (from the French, resembling a loaf of bread), marquise or navette ("little boat"), princess (square outline), heart, briolette (a form of the rose cut), and the pear or drop cuts. Generally speaking, these "fancy cuts" are not held to the same strict standards as Tolkowsky-derived round brilliants. Cuts are influenced heavily by fashion; baguettes—which accentuate a diamond's lustre and downplay its fire—were all the rage during the Art Deco period, whereas the princess cut—which accentuates a diamond's fire rather than its lustre—is currently gaining popularity. The princess cut is also popular amongst diamond cutters: of all the cuts, it wastes the least of the original crystal.
 
In the 1970s, Bruce Harding developed another mathematical model for gem design. Since then, several groups have used computer models (e.g., MSU, OctoNus (http://www.cutstudy.com), GIA (http://www.gia.org), and folds.net (http://www.folds.net/diamond/index.html)) and specialized scopes to design diamond cuts.
 
During the 1990s Israeli interests, centralized in Ramat Gan, acquired about 20% of the diamond trade, buying diamonds from Russia and from mines in Africa not controlled by De Beers. De Beers now deals only in diamonds from their own mines. A major diamond cutting industry has grown up in Gujarat State, India where 90% of the world's diamonds (as measured by number of diamonds) are cut by a workforce of 800,000[4] (http://www.vibrantgujarat.com/sp-gems.html). Small diamonds previously not worth cutting are cut in India, opening up a new market segment for small diamonds.
 
Some cuts are:

1) Round
2) Radiant
3) Pear
4) Marquise
5) Emerald
6) Oval
7) Heart
8) Princess


 
The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations. As far as the shape of the cut is concerned, it is very much a personal taste and preference. However, when jewelers judge the quality of a cut diamond, they often rate "Cut" as the most important of the "4-Cs." The key is not the shape, but how well the cutters executed that shape. The proportion, symmetry and quality of the polish are essential criteria of a good cut. Since the "brilliance" and "fire" of a diamond depends very much on the angle of the facets in relation to each other. A poorly cut diamond with facets cut only a few degrees from optimal will result in a stone that lacks the gem quality. For a round brilliant cut, there is a balance between "brilliance" and "fire". When a diamond is cut for too much "fire", it would look like a cubic zirconia which gives out much more "fire" than real diamond. A well executed round brilliant cut should reflect most light out from the tabletop and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows.
 
Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating. Since the per-carat price of diamond is much higher when the stone is over one carat (200 mg), many one-carat diamonds are the result of compromising "Cut" for "Carat". Some jewelry experts advise consumers to buy a 0.99 carat diamond for its better price or buy a 1.10 carat diamond for its better cut. A 1.00 carat diamond is usually poorly cut stone.
 
Cut Grading
 
The "Cut" of the "4-Cs" is the most difficult part for a consumer to choose in selecting a good diamond because a GIA certificate will not show the important measurements influencing cut (i.e. pavilon and crown angle) and will not provide a subjective ranking of how good the cut was. The other 3-Cs can be ranked simply by the rating in each category. It requires a trained eye to see the quality of a good "cut".
 
Several groups have developed diamond cut grading standards.
 
  • The AGA standards may be the strictest. David Atlas (who developed the AGA standards) has suggested that they are overly strict.
  • The HCA changed several times between 2001 and 2004. As of 2004, an HCA score below two represented an excellent cut. The HCA distinguishes between brilliant, Tolkowsky, and fiery cuts.
  • The AGS standards will change in the first quarter of 2005 to better match Tolkowsky's model and Octonus' ray tracing results.
 
The distance from the viewer's eye to the diamond is important. The 2005 AGS cut standards are based on a distance of 25 centimeters (about 10 inches). The 2004 HCA cut standards are based on a distance of 40 centimeters (about 16 inches).
 
Clarity
 
Clarity is a measure of internal structural imperfections called "inclusions". Grades of clarity, which are mostly those used by Gemological Institute of America (GIA), are:

  • FL - "flawless" in that no inclusions are visible under 10 times magnification
  • IF - "internally flawless" with no inclusions visible under 10 times magnification, only small blemishes
  • VVS1 and VVS2 - "very very small" inclusions that are difficult to see under 10 times magnification. VVS1 is a better grade than VVS2.
  • VS1 and VS2 - "very small" inclusions and visible under magnification but invisible to the naked eye.
  • SI1 and SI2 - "small inclusions" that can be noticeable to the naked eye, if you know where to look.
  • "SI3" is a grade sometimes used in the industry, originally popularized by the European Gemological Laboratory (EGL) Los Angeles grading office. While theoretically a range including lower SI2 and upper I1, it's commonly used to mean I1's which are "eye clean", that is, which have inclusions which aren't readily visible to the naked eye. Neither the GIA nor the American Gemological Society (AGS), the most reputable well known US labs, assign this grade.
  • I1, I2 and I3 - "imperfect" and visible to the naked eye. For I3, the inclusions impact the brilliance of the diamond and are large and obvious.
 
All grades reflect the appearance to an experienced grader when viewed from above at 10x magnification, though higher magnifications and viewing from other angles are used during the grading process. In "colorless" diamonds, dark inclusions will tend to create the greatest drop of clarity grade. In other colors pale inclusions may have greater relief (may stand out more) and may cause a greater drop in grade.
 
 
 
 
 
 
 

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