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How to value your diamond using the 4cs, which diamond certificates are accepted and which grade labs grade to a weaker standard. Don’t be confused, please call me or e mail me.
COLOUR, CLARITY, CUT, CARAT -
The 4Cs is a systematic method of grading a diamond for its value through its properties based on a scale collaborated together to establish its value.
The grading system is an international system and is used by all credible gem labs rated with an iso or international standard rating. To grade a diamond for the 4Cs it has to be unset and totally clean and free from dust.
COLOUR, CLARITY, CUT, CARAT
A diamond’s colour is determined by viewing it under controlled lighting (white light or an approx. colour temperature of 5500 degrees Kelvin), through the pavilion.
The diamond being graded is compared to a set of diamonds of known colour called master diamonds. Diamonds are graded on a color scale from D (colorless) to Z for natural fancy colors such as blue, green, yellow, brown, orange and, very rarely, red. These diamonds, called ‘fancies’ are incredibly rare and valuable.
The corresponding descriptions below are the colour grades for grading white diamonds and they are as follows.
D (exceptional white +)
E (exceptional white)
F (rare white+)
G (rare white)
I and J (slightly tinted white)
K to Q (tinted)
The price difference for each colour grade is approx 7-10%.
In making your assessment, take into account that diamonds that are G and H colour will look very white when set and viewed through the crown as opposed to through the pavilion while being graded.
We recommend you to purchase a higher colour and slightly lower clarity such as a VS2, SI1 or SI2 (except emerald cut) as it may be easier to differentiate colour to the naked eye as opposed to clarity.
A diamond must be graded for clarity with a 10 times stereo binocular microscope after the stone has been carefully cleaned and must be continually wiped while grading for inclusions that are above VS2 clarity. The price between each clarity grade is approximately 7-10%.
The clarity grades are as follows
F or FL
Flawless. The diamond shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader. Note: Truly flawless or internally flawless (F or IF on the GIA’s grading scale) diamonds are extremely rare.
VVS1/ VVS2 (Very Very Slight)
Very, Very slightly included. The diamond contains minute inclusions that are difficult even for experienced graders to see under 10X magnification.
VS1/ VS2 (Very Slight)
Very slightly included. The diamond contains minute inclusions such as small crystals, clouds or feathers when observed with effort under 10X magnification.
SI1, SI2 (Small or Slight)
Slightly included. The diamond contains inclusions (clouds, included crystals, knots, cavities, and feathers) that are easily noticeable to an experienced grader under 10X magnification.
Included The diamond has inclusions which are easy to see with the 10X magnification but which are hard to see with the naked eye. This grade should not diminish the brilliance.
Included. The diamond contains inclusions (possibly large feathers or large included crystals) that are obvious under 10X magnification and may affect transparency and brilliance and are easy to see with the naked eye
When choosing a clarity grade we recommend a VS2, SI and in cases an SI2 clarity grade for fancy brilliants as the facets disguise the larger SI2 type inclusions which often cannot be seen at all with the naked eye when set. Remember that diamonds that are not fancy brilliants like an emerald cut may show SI inclusions that are visible to the naked eye, so when choosing this cut we recommend a clarity grade from VS2 upwards.
There are two aspects of cut.
One is the physical shape of the diamond the other is the proportion of the cut grade.
The round brilliant cut diamond is the most ideal shape to maximise brilliance and is the most expensive shape or cut. All other shapes are termed ‘fancy cuts’ and are approx 20% less in value than round brilliant cuts of matching quality.
Proportion of Cut.
Put most simply, many expensive commodities look poor or out of proportion when manufactured poorly. The cut of the diamond should be manufactured or cut to the scientific ideal proportions or tolerances. The cutter should choose to adhere to these statistics based on the individual piece of rough and what yields the maximum value within these tolerances for the finished piece. A poorly cut diamond looks dull and has incorrect dimensions and is worth substantially less then one that is well cut with the corresponding colour and clarity grades.
The ideal tolerances for a diamond are as follows and are listed on the diamond certificate.
Total diameter 100%
Table size 52-64%
Crown height 12-18%
Girdle thickness 2-5%
Pavilion depth 42-45%
Crown angle 34.5 degrees
Pavilion angle 43.5 degrees.
The overall cut grade or proportion of cut is assessed and written on the certificate under symmetry as well as the individual proportions of each category listed above. If the stone is within the ideal tolerance range then it will get a very good proportion of cut, a variance of 5% will yield a good proportion of cut, a variance of 10% will yield a medium proportion of cut, a variance of 15% will yield a poor proportion of cut.
A Carat is an expression of weight and is a fifth of a gram, therefore a five carat diamond will have a weight of one gram. The carat took its name from the carob seed which in nature has a consistent weight of a fifth of a gram. The weight of the stone is indirectly responsible for the size as stones cut to different proportions can have different sizes across the top of the diamond. Proportion of cut is important because a good proportioned cut diamond (well cut) can have very different dimensions to a stone that is medium or poorly cut resulting in different depths and light reflection and refraction through the stone. The facets may not be symmetrical giving black or dull portions of the diamond, therefore carat is an expression of weight which does not necessarily relate to size.
Diamonds are valued in weight categories as follows:
These categories are used to establish a consistent system for values of diamonds between certain size brackets. (Rapaport List) For eg if a diamond had a colour of G, a clarity of VS2, a very good proportion of cut, nil fluorescence and the same shape of cut, then the value of the diamond increases substantially in each size bracket not only by the weight but by the amount of the price increase of the price bracket above it.
One of the characteristics of diamonds is that they react to ultraviolet light. This is one of the many ways they are detected from other minerals when they are mined.
For gem quality diamonds it is important that the grade of fluorescence is stated on the certificate. All iso rated laboratories will have the fluorescence grade on the diamond grading report or certificate.
Gem quality diamonds are tested in certain UV wavelengths that are important for the visual effects the human eye can detect.
The grades are as follows
None or nil
V slight or slight
We recommend all our clients purchasing diamonds to select a diamond which displays slight or no fluorescence as diamonds which are strongly reactive to UV light react in the sunlight and have a masked, slightly oily or blurred effect when they fluoresce in sunlight or UV light.