All about DiamondsDiamonds

Colour: Colourless, yellow, brown, rarely green, blue, reddish, orange black
Transparency: Transparent to opaque
Colour Of Streak: White
Refractive Index: 2.417-2.410
Moh's Hardness: 10
Double Refraction: None
Density: 3.50-3.53
Dispersion: 0.44(0.025)
Cleavage: Perfect
Absorption: Colourless and yellow D, 478, 465, 451, 435, 423, 415, 435, 401,  390;
Brown and greenish D, (537), 504, (498)
Fracture: Conchoidal to splintery
Pleochroism: None
Crystals: (Cubic), mainly octahedrons, also cubes, rhombic dodecahedrons, twins, plates
Flourescence: Very variable;
 Colourless and yellow D, mostly blue
 Brown and greenish D, often green
Chemical Composition: C, Crystallized carbon

The King Of The Gemstones
The name Diamond refers to its hardness (Greek—adamas, the unconquerable). There is nothing comparable to it in hardness. Its cutting resistance is 140 times greater than that of ruby and sapphire, the gemstones next in hardness after diamond. However the hardness of a diamond is different in the individual crystal directions. This allows one to cut diamond with diamond and/or with diamond powder. Because of the perfect cleavage, care must be taken not to accidently bang against an edge of a diamond, and also when setting it. Its very strong luster sometimes enables the experienced eye to differentiate between a diamond and its imitations. Diamond is generally insensitive to chemical reactions. High temperatures, on the other hand, can induce etchings on the facets. Therefore special care must be taken during soldering! In the last fifty years, it has been recognized that there are various types of diamonds with different characteristics. Science differentiates between type la, Ib, IIa, and IIb. This is of little importance to the trade, but does assist the cutter. Due to the optical effects, the high hardness, and its rarity, the diamond is considered the king of gemstones. It has been used for adornment since ancient times.


Valuation of Diamonds
All diamonds that De Beers brings on the market are classified beforehand into one of the 5,000 different standards of quality, according to form, quality, colour, and size Besides London, there are such sorting centers in Lucerne in Switzerland, Gaborone in Botswana, Windhoek in Namibia, and Kimberley in South Africa.
Formerly, 20 percent of all diamonds were considered suitable for jewellery, having been of "gemstone quality." The rest were sold to the industry as so-called industrial diamonds to be used for drilling crowns, milling machines, cutting wheels, etc. Since 1983, another 20 percent have been classified as "almost gemstone quality" and are cut mainly in India. The smallest diamonds and diamonds of lesser quality can be worked and offered to buyers other than the strictly controlled diamond market.

In the valuation of faceted diamonds, colour, clarity, cut, and carat are taken into consideration. These four c's decide the value of a diamond.

Grading for Colour
Diamonds are found in all colours. Mostly they are yellowish. In the grading, these are evaluated together with the purely colourless diamonds. The rarer strong colours (green, red, blue, purple, and yellow), the so-called fancy colours, are valued individually and fetch collector's prices. Brown and black diamonds also occur
Formerly, terms and definitions in grading for color were not uniform and often confusing, until an international agreement was reached to cover the so-called "yellow series." This was published in 1970 as RAL 560 A5E. Since then, various institutions have come up with improved guidelines, especially the Gemological Institute of America (GIA), the International Diamond Council (IDC), and the Confederation Internationale de la Bijouterie, Joaillerie, Orfevrerie des Diamants Perles, et Pierres (CIBJO). Today, the IDC regulations, written in English, are accepted worldwide. In the United States, the GIA system is most commonly used
The old grading terms, the "Old Terms," should not be used anymore. In fact, however, they are still in usage in the gemstone trade.
Experts use standard sample collections for consistent, comparison color grading.

Colour Grading of Faceted Diamonds

CIBJO IDC GIA Old Terms RAL 560 A5E
very fine white + very fine white exceptional+ white
exceptional white
D E River blue-white
fine white+ fine white rare white + rare white F G Top Wesselton fine white
white white H Wesselton white
slightly tinted white slightly tinted white I J Top Crystal weakly tinted white
tinted white tinted white K L Crystal tinted white
tinted 1 tinted colour1 M N Top Cape weakly yellow
tinted 2 tinted colour 2 O P Cape yellowish
tinted 3 tinted colour 3 Q R Light Yellow weakly yellow
tinted 4 tinted colour 4 S-Z Yellow yellow


Grading for Clarity
In Germany only the inner perfection is understood as "clarity while in the United States and in Scandinavia aspects of the quality of the outer finish are taken into consideration. Enclosed minerals, cleavages, and growth lines affect clarity; they are collectively called inclusions, but formerly were called "flaws" "carbon spots." Polished diamonds without any inclusions under a 10 X loupe are considered "flawless." Inclusions visible with larger magnification are not taken into account for grading.

 

Grading for Clarity of Faceted Diamonds
CIBJO Definition GIA
Lr flawless Free of inclusions under 10 X magnification and absolutely transparent If internally flawless
VVS very very small inclusions Very few, very small inclusions, under 10 X magnification very difficult to see VVS 1 very very VVS 2 slightly included
VS very small inclusions Very small inclusions, under 10 X magnification difficult to find VS 1 very slightly included VS 2 slightly included
SI small inclusions Small inclusions, easily recognized under 10 X magnification SI 1 slightly included SI 2 slightly included
PI distinct inclusions Inclusions, immediately recognized under 10 X magnification, but not diminishing brilliance 11 included I
P11 larger inclusions Larger and/or numerous inclusions slightly diminishing the brilliance recognizable with the naked eye 12 included II
P111 large Large and/or numerous inclusions, diminishing the brilliance considerably 13 included III

According to CIBJO, it is permitted to subdivide the clarity grades WS, VS, and SI into two subgroups each, for stone sizes over 0.47 ct. Definitions assume a trained grader working under favourable conditions.

Grading for Cut
To grade for cut, the type and shape of cut, proportions, and symmetry as well as outer marks are taken into consideration. In Germany the normal cut is the "fine brilliant cut", in the rest of Europe the "Scandinavian-standard brilliant." In the United States, the only widely used cut grading system is that of the American Gem Society, based on the "AGS Ideal Cut." The following table shows the terms and definitions for grading in a simplified form, according to the RAL 560 A5E, published in 1971.

Grading of Cut of the Diamond Brilliants

RAL 560 A5E Definition
Very good Exceptional brilliance. Few and only minor outer marks. Very good proportions.
Good Good brilliance. Some outer marks. Proportions with some deviations.
Medium Slightly less brilliance. Several larger outer marks. Proportions with considerable deviations.
Poor Brilliance considerably less. Larger and/or numerous outer marks. Proportions with very distinct deviations.