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Diamond Cut, Colour, Clarity, Carat Weight

What is Diamond : Diamond Grading : Is it a Diamond? : Diamond Help

  • Cut
  • Colour
  • Clarity
  • Clarity Enhancements
  • Carat Weight
  • Certificates
  • The Diamond 4C's

    Cut

    The main diamond cuts are:
    Round Brilliant Round Brilliant Diamond Emerald Cut Emerald Cut Diamond Princess Cut Princess Cut Diamond Heart Cut Heart Cut Diamond
    Oval Cut Oval Cut Diamond Marquise Cut Marquise Cut Diamond Pear Cut Pear Cut Diamond Round Brilliant Round Brilliant Diamond

    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

    Cut The most popular cut is the modern round brilliant (R/B):

    Round Brilliant Diamond top view Round Brilliant Diamond side view

    Round Brilliant Facets

    The standard brilliant comprises:

    Upper:

    1 Table facet
    8 Star facets
    8 Kite or Upper Main Facets
    16 Upper Girdle facets

    Total facets: 33 Crown Facets

    facets on a round brilliant cut diamond

    Girdle:

    This is the waist band in the middle, and is sometimes faceted.

    Pavilion:

    8 Pavilion
    16 Lower Girdle
    1 Culet

    Total facets: 25 Pavilion Facets

    Thus there are 58 facets in total.

     

    facets on a round brilliant cut diamond

    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)

    CriteriaUnusualGoodVery GoodGoodUnusual
    Crown Angle< 26.927.0 to 30.630.7 to 37.737.8 to 40.640.7 +
    Pavilion Angle< 38.438.5 to 39.539.6 to 42.242.3 to 43.143.2 +
    Table width71%+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 thicknessextremely thinvery thinthin & mediumthick & V thickextremely 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%+

    Cut Ratio

    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.

    Proportions %diameterIdeal Brilliant 1926Parker Brilliant 1951Tolkowsky Brilliant 1919Practical Fine Cut 1939Standard Brilliant 1969Eulitz Calculated Brilliant 1972
    Crown Height19.2%10.5%16.2%14.4%14.6%14.45%
    Girdle Thickness-----1.5%
    Pavilion Depth40.0%43.4%43.1%43.2%43.1%43.15%
    Table Diameter56.1%55.9%53.0%56.0%57.5%56.5%
    Crown Facets Angle (to girdle)41.125.534.533.234.533.36
    Pavilion Facets (to girdle)38.740.940.7540.840.7540.48
    Crown Height: Pavilion Depth1:2.071:4.131:2.661:31:2.951:3
    Light Yield29.88%42.39%32.39%33.03%--
    Brilliance Grade98.4%Low99.5%99.95%99.5%100%

    To find out more about the Brilliant cut click here:
    Round Brilliant

    Colour

    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:

    Colour: Description:
    DPure White - the most prized colour
    EExceptional white - colourless group
    FExcellent white - colourless group
    GGood white - colourless group
    HWhite - colourless group
    ISlightly tinted white/ white when viewed from top
    JSlightly tinted white/ commercial white
    KTinted white/ still acceptable white when mounted
    LTinted white/ needs yellow setting to look its best
    MSlightly yellowish/Tinted colour-champagne
    NSlightly yellowish/Tinted colour-champagne
    O-RYellowish/Tinted colour
    S-ZYellow/Tinted colour

    Fluorescence

    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.
    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 termed 'over-blue'.

    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 a premium.

    ColourFluorescenceIF-VVSVSSI-I3
    D EVery 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
     Weak000
    F G HVery Strong-7% to -10%-3% to -5%0
     Strong-5% to -7%-2% to -3%0
     Medium-1% to -3%0 to -2%0
     Weak000
    I J KVery Strong0 to 3%0 to 3%0 to 3%
     Strong0 to 2%0 to 2%0 to 3%
     Medium0 to 2%0 to 2%0 to 2%
     Weak000

    Clarity

    Clarity:Number and SizeExpert-10x loupeNaked EyeInfluence on Brilliance
    IFno inclusions-internally flawlessnothingnothingnone
    VVS1very very small inclusions, pin pricksvery difficultnothingnone
    VVS2very very small inclusions, pin pricksvery difficultnothingnone
    VS1very small, still minutedifficult to seenothingnone
    VS2very small, still minutedifficult to seenothingnone
    SI1tinyeasily seennothingnone
    SI2tinyeasily seennothing from topnone
    I1smallrecognisable immediatelydifficult to recognisenone
    I2larger and/or numerous inclusionsobviousrecognisable immediatelyslight
    I3large and/or numerousvery obviousvery easily recognisedheavy influence

    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.

    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.

    Enhancements

    Laser Drilling

    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.

    Filled Diamonds

    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.

    Carat Weight

    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.

    Weight: Size (diameter):Weight: pts (diameter):Weight: fractions
    0.05ct1.00mm5pts1/20th
    0.10ct3.00mm10pts1/10th
    0.20ct3.85mm20pts1/5th
    0.25ct4.10mm25pts1/4
    0.33ct4.55mm33pts1/3rd
    0.40ct4.80mm40pts
    0.50ct5.15mm50pts1/2
    0.66ct5.72mm66pts2/3
    0.75ct6.00mm75pts3/4
    0.90ct6.40mm90pts
    1.00ct6.65mm100pts1 carat
    1.50ct7.50mm150pts1 1/2
    2.00ct8.10mm200pts2 carats

    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 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.

    Certificates

    Where 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:

    Code: Laboratory:
    ADLAntwerp Diamond Laboratory
    AGAAmerican Gem Apraisal Laboratories
    CIBCIBJO (Europe)
    CSAJewellery Council of South Africa
    DGLDiamond Grading Laboratories (London)
    EGIEuropean Gemmological Institute (Antwerp)
    EGLEuropean Gemmological Institute (Antwerp & London)
    PNFP N Ferstenberg Pbv A
    GAGGesellschaft fur Angewandte Gemmologie
    GANGemological Institute of Antwerp
    GIAGemological Institute of America
    GIINational Gemological Institue of Israel
    GILGem Information Laboratory
    GTLGem Testing Laboratory of Great Britain
    NGLNorthern Gemmological Laboratories (UK)
    HRDDiamond High Council (Antwerp)
    HRGHeinz R Gartner, DGemG, FGA (Germany)
    IGIInternational Gemmological Institute (Antwerp)
    PSLPrecious Stone Laboratory (London)
    VPTVerena Pagel-Theisen, DGemG FGA (Germany)
    WGWerner Galia, DGem, (Germany)

    We sell diamonds issued with a GIA, AGS or HRD certificate, but other certificates may be available on request.

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