WHAT IS A GEM DIAMOND? GEM DIAMONDS – A DEFINITION, By RD Ferraris
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THE ULTIMATE GEM
Diamonds are separated into two different types; namely Type I and Type IIa. Type I diamonds contain nitrogen while Type IIa diamonds are nitrogen free and are usually white, brown or pink and very rarely red or green. Type IIa and Type IIb (blue colour) are very rare and generally thought to comprise less than 1% of all diamonds. Because of the absence of nitrogen, Type IIa diamonds can never be yellow. While it is possible to obtain D Flawless diamonds from Type I diamonds, the most sought after diamonds are Type IIa Flawless diamonds. Type II diamonds have superior optical properties and have a superior overall polish to Type I diamonds.
In ancient times, incredible white diamonds were recovered in Golconda in India, and to this day Golconda diamonds have held a superior position to white diamonds produced anywhere else in the world. However, notwithstanding these Golconda gems, the Gem Diamonds Marketing Consultants and some of the world's leading Diamantaires believe that the D Flawless diamonds from Letšeng are the prize gems of them all.
ROUGH GEM QUALITY DIAMONDS
These diamonds are attractive when viewed and are the easiest diamonds to manufacture and polish for jewellery.
Gem quality diamonds are based on the combination of the following characteristics:
To a large degree size does matter, especially with large white D, E F & G colours. However, when dealing with rare fancy colours such as reds, blues, oranges and greens, even small stones are highly prized gems.
A range of white, moving to lighter yellows and browns are regarded as gem colours, with the whiter colours being the highest value colours. Deeper colours of yellow and brown, as well as unusual colours such as orange, violet, purple, green, pink, blue and red are referred to as fancy colours.
Originally gem quality rough diamonds were those diamonds without cracks, twins or large inclusions, the equivalent of the polished grade SI3 or better. Lesser qualities were referred to as near-gem and included low clivage and semi-opaque rejection material.
In today's terminology, the better near-gem qualities are included as gem quality, as it is now viewed that any diamond which can provide a polishable gem be included, regardless of the fact that more splits (sawing, cleaving or lasering) are required to achieve polishable pieces.
The most desired rough gem shapes are the following:
crystals (Sharp edged octahedrons),
octahedrons with some rounding to the edges and points
rounded dodecahedral maccles
shapes that have high yielding forms either for rounds or fancy cuts
Less desirable gem shapes are cubes, irregular low yielding shapes and twinned or aggregated forms.
Other factors which influence the overall gem description would include white or fancy colour diamonds that have high blue fluorescence or stones with unattractive clouds, milkiness or colour banding/zoning.
Therefore, the most desired rough gem diamonds would be those having good colour, shape and internal clarity, without ignoring the size factor.
POLISHED GEM DIAMONDS
Based on the descriptions above, a polished gem diamond requires the basic 4 C's:
The size of the polished gem does matter and is further complicated by reaching stipulated price bands, such as 0.25ct, 0.50ct, 1.00ct, 3.00ct, 5.00ct, and 10.00ct and so on. The price difference between a 0.99 carat and a 1.00 carat is very high and this continues throughout all the size bands.
After size, colour is the first step to the pricing of a diamond, and as with the rough, the whiter colours are the most sought after. Fancy colours are in a different set of price bands altogether and are affected by the saturation of the colour as well as colour overtones such as orangey-pink, etc.
The internal quality is very important and there are large price differentials between Internally Flawless and VVS, etc. Therefore, the higher the clarity, the more prized and expensive the polished gem becomes.
Rounds are the most desired cut or shape, followed by fancy cuts such as the Princess and Pear cuts. Fancy cuts are always discounted to the round shape and this decreases according to the cut with shapes such as the Heart and Trilliant as well as some obscure shapes having the highest discount.
OTHER IMPORTANT FACTORS FOR POLISHED GEMS
QUALITY OF POLISH
The quality of the cut in terms of actual polishing such as Cut Grade, Polish and Symmetry is essential in achieving the incredibly rare clarity rating of Flawless gems. Therefore, it is essential that if you have the correct size, for example a 1.05 carat polished stone, it should be a D colour round brilliant shape diamond that has no internal or external blemishes and be graded Excellent for the Cut Grade, Polish and Symmetry. The stone should have zero fluorescence.
The above description is the highly prized and rare D Flawless diamond. It is estimated that of all the diamonds mined only 0.001% will produce D Flawless finished stones. [Bryan Boyne, G.G. (GIA)].
The quality of polish and symmetry is vital to achieve maximum brilliance, scintillation ('sparkle') and dispersion ('fire').
As with rough diamonds, there are other factors which influence the overall gem description would include white or fancy colour diamonds that have high blue fluorescence or stones with unattractive clouds, milkiness or colour banding/zoning.