Diamond Cut, Colour, Clarity, Carat Weight
The Diamond 4C's
The main diamond cuts are:
Popular diamond cuts include Heart, Emerald, Marquise (Oval with pointed ends), Oval, Pear, and Princess. There are unusual cuts appearing all the time such as the J C Millennium which is basically a Round Cut stone similar to the Round Brilliant, and the Radiant Cut which is an octagonal stone similar to an Emerald or Step Cut with upper girdle facets similar to the Princess Cut which is a square stone. If you would like more detailed information on any particular cut just e-mail customer services.E-mail: Help
The most popular cut is the modern round brilliant (R/B):
Round Brilliant Facets
The standard brilliant comprises:
1 Table facet
8 Star facets
8 Kite or Upper Main Facets
16 Upper Girdle facets
Total facets: 33 Crown Facets
Girdle:This is the waist band in the middle, and is sometimes faceted.
There are many ideal cuts or sets of proportions and facet angles for the round brilliant cut. Below are the proportions for a brilliant in percentages of girdle diameter according to the IDC (International Diamond Council formed in 1979)
16 Lower Girdle
Total facets: 25 Pavilion Facets
Thus there are 58 facets in total.
|Crown Angle||< 26.9||27.0 to 30.6||30.7 to 37.7||37.8 to 40.6||40.7 +|
|Pavilion Angle||< 38.4||38.5 to 39.5||39.6 to 42.2||42.3 to 43.1||43.2 +|
|Table width||71%+||70% to 67%||66% to 53%||52% to 51%||< 50%|
|Crown height||< 8.5%||9% to 10.5%||11% to 16%||16.5% to 18%||18.5% +|
|Girdle thickness||extremely thin||very thin||thin & medium||thick & V thick||extremely thick|
|Pavilion Depth (for pointed culet)||< 39.5%||40% to 41%||41.5% to 45%||45.5% to 46.5%||47%+|
|Culet Size|| || ||pointed to 1.9%||2% to 3.9%||4%+|
|Total depth||< 52.9%||53.0% to 55.4%||55.5% to 63.9%||64% to 66.9%||67.0%+|
It can be seen therefore that a ratio can be realised for any given brilliant cut diamond, and which when calculated, will yield its deviation from the 100% brilliance of the Eulitz Cut (mathematically perfect). We can calculate this for you when you purchase a diamond from us and it indicates mathematically how well your diamond has been cut. We generally reject stones that fall below 9% deviation. You might think this is a hard line approach, but we want you to be delighted and so we always aim to supply you with diamonds that exceed your expectations.
Types of Brilliant cut:
The 'Ideal' round brilliant cut has changed through out history, but in 1972 Euliz calculated the proportions necessary for 100% brilliance in a diamond. We are currently translating the work from German and will provide more information on the solution in the near future.
To find out more about the Brilliant cut click here:Round Brilliant
|Proportions %diameter||Ideal Brilliant 1926||Parker Brilliant 1951||Tolkowsky Brilliant 1919||Practical Fine Cut 1939||Standard Brilliant 1969||Eulitz Calculated Brilliant 1972|
|Crown Facets Angle (to girdle)||41.1||25.5||34.5||33.2||34.5||33.36|
|Pavilion Facets (to girdle)||38.7||40.9||40.75||40.8||40.75||40.48|
|Crown Height: Pavilion Depth||1:2.07||1:4.13||1:2.66||1:3||1:2.95||1:3|
There are many differing scales used by different organisations for colour, but the most common one is an alphanumeric scale starting at the colour D. This is the whitest colour exhibited by diamond. A typical commercial colour seen in jewellery shops in the UK is probably around J to K which is still very pleasing when set in a ring. To give you a feel for the colours we have prepared a table below:
Around two thirds of diamonds fluoresce to some extent under both artificial, and natural ultra violet or UV light. The bright rich purple type of lamp found in sun bed and pubs/clubs, is a typical artificial UV source. Sun light is of course a natural source of ultra violet light, and most diamonds that flouresce srongly will take on a bluish tint. This phenomena has consequences for colour grading because a strongly fluorescing diamond will appear to have a different colour when viewed in strong sunlight than it does when viewed under artificial light in your home.
|D||Pure White - the most prized colour|
|E||Exceptional white - colourless group|
|F||Excellent white - colourless group|
|G||Good white - colourless group|
|H||White - colourless group|
|I||Slightly tinted white/ white when viewed from top|
|J||Slightly tinted white/ commercial white|
|K||Tinted white/ still acceptable white when mounted|
|L||Tinted white/ needs yellow setting to look its best|
|M||Slightly yellowish/Tinted colour-champagne|
|N||Slightly yellowish/Tinted colour-champagne|
When blue flourescence is observed in colourless diamonds these diamonds are additionally described as JAGER, indicacating their property of fluorescence. Jager (from the South African Jagerfontein mine) is not to be confused with an old term for describing the best white diamonds. The Jager or 'blue white' colour, it was realised, was in fact a 'D' colour diamond which exhibited fluorescence and hence Jager is no longer used in this respect.
Diamonds with a slight yellow tint when mixed with the bluish glow from fluorescence may appear a better colour, or less yellow, than they are in artificial light. Colour grading is therefore performed under an ultra violet free source and then graded for fluorescence separately. We use white light of colour temperature between 5000/5500 Kelvin to colour grade. To examine fluorescence we use two forms of artificial UV light, mostly long wave UV (LWUV) producing radiation at 365nm and Short Wave (SWUV) radiation at 254nm (nm=nanometre or 0.000000001 metre). Most fluorescent diamonds are excited by long wave UV and just a few at shorter wavelengths.
In the GIA system two comparison Master stones are used and these are located
at the borders between faint/medium and medium/strong. This permits five grades:
NONE, FAINT, MEDIUM, STRONG and VERY STRONG. The strength is a direct comparison
with the two master stones. Fluorescence is not always a good thing though.
A few diamonds exhibit a yellow fluorescent glow which will make the diamond
appear to be a colour grade worse in UV rich sunlight. Extremely fluorescent
tinted diamonds exhibit a milky-bluish or petrol-coloured effect and are often
Fluorescence: Influence on price
The nature of blue fluorescence on price is dependent on its visual impact.
For higher colour stones, strong fluorescence causes a detrimental milky
effect which lowers the value, see table below. However at the other end
of the scale with lower coloured stones, strong fluorescence will attract
|D E||Very Strong||-10% to -15%||-6% to -10%||0 to -3%|
| ||Strong||-7% to -10%||-3% to -5%||0 to -1%|
| ||Medium||-3% to -7%||-1% to 2%||0|
|F G H||Very Strong||-7% to -10%||-3% to -5%||0|
| ||Strong||-5% to -7%||-2% to -3%||0|
| ||Medium||-1% to -3%||0 to -2%||0|
|I J K||Very Strong||0 to 3%||0 to 3%||0 to 3%|
| ||Strong||0 to 2%||0 to 2%||0 to 3%|
| ||Medium||0 to 2%||0 to 2%||0 to 2%|
Clarity is an indication of a diamond's purity. It describes the degree to which a diamond is free of imperfections. The internal clarity grades range from internally flawless (IF) to fairly included (I3)or third pique (pronounced peekay) also written P3.
Flaws in diamonds may include external blemishes (from naturals and polishing defects) and internal inclusions. Most blemishes are so small as to have no affect on the beauty or brilliance of the stone. In nearly all diamonds, traces of minerals, gasses or other elements were trapped inside during the crystallization process. Inclusions look like tiny crystals, clouds, or feathers and are unique to every diamond. It is very rare to find a diamond that is completely clean to the expert eye using magnification.
The clarity of a diamond is graded by how many, how big and how visible the inclusions are, and where they are located within the diamond. The fewer and smaller the inclusions, the more rare and valuable the diamond. It is very rare to find an internally flawless (IF) diamond.
|Clarity:||Number and Size||Expert-10x loupe||Naked Eye||Influence on Brilliance|
|IF||no inclusions-internally flawless||nothing||nothing||none|
|VVS1||very very small inclusions, pin pricks||very difficult||nothing||none|
|VVS2||very very small inclusions, pin pricks||very difficult||nothing||none|
|VS1||very small, still minute||difficult to see||nothing||none|
|VS2||very small, still minute||difficult to see||nothing||none|
|SI2||tiny||easily seen||nothing from top||none|
|I1||small||recognisable immediately||difficult to recognise||none|
|I2||larger and/or numerous inclusions||obvious||recognisable immediately||slight|
|I3||large and/or numerous||very obvious||very easily recognised||heavy influence|
Grading according to discernability of inclusions:
It can be seen that diamonds graded SI2 and better will appear to be perfect, and no loss of brilliance will be detected. Combined with a good cut and colour of H or better, we have a perfect diamond for any piece of jewellery.
Lasers have been used commercially for drilling diamonds since the late 1960's. It is possible to improve the appearance of diamonds which have dark magnetic pyrites and magnetite inclusions by drilling into the diamond surface and then bleaching out or chemically dissolving the inclusions with an etching fluid such as sulphuric acid and saltpetre. The drill holes are then usually filled with a highly refractive wax or synthetic resin and this protects the drill chanel against penetration of dust and dirt. This can be affected if your diamond is ever subjected to heat or acid as often is the case when being set in jewellery or worked on by an unsuspecting working jewller. Although the treatment is fairly permanent, we will not sell you a diamond that has been drilled.
This is a more recent enhancement by which inclusions and especially cracks which break the surface can be made more transparent and hence improve the clarity of a cut diamond. The cracks are filled under pressure (50 atmospheres) in a vacuum at high temperature (400 degrees Celcius) with a glass of refractive index close to that of diamond at 2.417. A colour flash similar to that on the surface of a detergent bubble is visible due to the juxtaposition of the two different materials. Unfortunately the process though widely used is neither durable or permanent and will not withstand the cutting and repair processes involved in jewellery work. We will not sell you a diamond that has been filled.
The weight of a diamond and is measured in Carats. 1 Carat equals 0.2 gram and there are 100 points to a carat. Thus a 50 point diamond is half a carat (0.50ct) and weights 0.1 gram. A Grain, no longer used, is accepted to be 0.050 grams. Many dealers still use the terms a grainer meaning 0.25ct, two grainer - half carat, six grainer- 1.5 carats etc.
There is an approximate relationship between weight and diameter of a round brilliant cut diamond. This is useful when trying to estimate the size of a diamond.
Most diamonds are accurately weighed on an electronic scale to the nearest 1000 th of a carat (0.001). If a stone weighs 0.009 it is rounded up and 0.008 is rounded down. This is standard practice in accordance with diamond club rules, but in all other industries 5 is rounded up and 4 is rounded down. Example:
|Weight: ||Size (diameter):||Weight: pts (diameter):||Weight: fractions |
Weight 2.329 carats will be described as 2.33 carats.
Weight 2.328 carats will be described as 2.32 carats
According to Trading Standards, jewellers are technically allowed to round up at the 5, hence 2.325 carats rounds up to 2.33 carats but this is frowned upon in the trade.
CertificatesWhere a diamond has been assessed by a laboratory it is termed a certificated or certified stone. The codes for the different laboratories used are as follows:
We sell diamonds issued with a GIA, AGS or HRD certificate, but other certificates
may be available on request.
|ADL||Antwerp Diamond Laboratory|
|AGA||American Gem Apraisal Laboratories|
|CSA||Jewellery Council of South Africa|
|DGL||Diamond Grading Laboratories (London)|
|EGI||European Gemmological Institute (Antwerp)|
|EGL||European Gemmological Institute (Antwerp & London)|
|PNF||P N Ferstenberg Pbv A|
|GAG||Gesellschaft fur Angewandte Gemmologie|
|GAN||Gemological Institute of Antwerp|
|GIA||Gemological Institute of America|
|GII||National Gemological Institue of Israel|
|GIL||Gem Information Laboratory|
|GTL||Gem Testing Laboratory of Great Britain|
|NGL||Northern Gemmological Laboratories (UK)|
|HRD||Diamond High Council (Antwerp)|
|HRG||Heinz R Gartner, DGemG, FGA (Germany)|
|IGI||International Gemmological Institute (Antwerp)|
|PSL||Precious Stone Laboratory (London)|
|VPT||Verena Pagel-Theisen, DGemG FGA (Germany)|
|WG||Werner Galia, DGem, (Germany)|
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