Mar 19 2004
Background
When selecting a diamond, most jewellers refer to the 4 C’s:
- Colour
- Carat or weight
- Clarity
- Cut
These four factors largely determine the value of a diamond.
Colour
Diamonds come in a range of colours from faint yellow or brown, through to very rare pinks, blues, greens and other colours known as fancies. The best colour for a diamond is no colour, i.e. a diamond that allows white light to pass through it effortlessly and be dispersed in a rainbow of colours.
The best colourless stones carry a grading allocated ‘D’. From here, grades are designated letters ranging all the way through the alphabet down to Z, for diamonds which may be light yellow, brown or grey. Colour gradings are difficult compare/determine without the correct conditions and equipment.
The colour of diamonds is determined by the presence of trace elements present in the atomic structure of the diamond. The more intense the colour, the further the grading descends down the scale.
Some colours occur extremely rarely and are calssified by a different scale. Such colours may include pinks, blues, greens, amber and red. As mentioned above, these colours are called ‘fancy colours’, with classifications dertermined by hue and saturation.
Carat or Weight
The weight of diamonds is measured in ‘carats’ (often abbreviated to ‘ct’), with diamonds being available in various weights and fractions of a carat. One carat is divided up into 100 points such that 0.75 carat is the same as ¾ carat.
The word carat is derived from the carob tree or Ceratonia Siliqua, which produces seeds of high uniformity and consistent weight. Diamonds and other gemstones were originally weighed against these seeds. More recently, one carat (or 100 points) has been standardised at 0.2grams
While size is a major determining factor in the price of a diamond, quality can also play a significant role. It should also be noted that the larger a diamond, the rarer it is, which will also have a bearing on its value.
Clarity
Almost all diamonds contain inclusions (often called birthmarks) which affect its clarity. There are an internal flaws or inclusions. External flaws also exist and may consist of surface irregularities or blemishes which also affect clarity.
Imperfections may not be seen by the naked eye but can be seen using microscopes operated at 10x magnification. Clarity of diamonds is graded using a complex method which evaluates the size, location and visibility of the inclusions.
The fewer the number of inclusions, the rarer the diamond and hence the higher its desirability and value. The type, size and number of imperfections influences a diamonds’ grade. These grades are summarised in table 1.
Table 1. Classifications of diamonds.
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Flawless and Internally Flawless
F1 & FL
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Flawless is the highest grade. These diamonds contain no detectable flaws when viewed with a microscope at 10x magnification.
Internally flawless diamonds contain no visible internal flaws when viewed with a microscope at 10x magnification, but have minor surface blemishes.
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Very Very Slightly Included
VVS1 & VVS2
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The classification is divided into 2 categories. They contain minute inclusions often only seen by experienced graders under a microscope at 10x magnification.
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Very Slightly Included
VS1 & VS2
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Again, this category is divided into 2 categories. They contain slight imperfections which are still difficult to detect under a microscope.
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Slightly Included
SI1 & SI2
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Also divided into 2 categories. These diamonds contain slight imperfections that can be seen under a microscope at 10x magnification.
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Included
I1, I2 & I3
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This category is divided into 3 classes, with increasing number indicating flaws that are more obvious, with some being visible to the naked eye.
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Cut
Often confused with the shape of a diamond. Diamonds are cut into many shapes, with the shape normally dictated by the shape of the rough diamond. This is only factor that is not dictated by nature.
When cut by a skilled diamond cutter, not only is the resultant diamond a sight to behold, but it is also better able to handle light, producing more scintillation and sparkle or brilliance.
A well cut diamond reflects light from one facet to another and then out through the top. A diamond cut too deep (called a nailhead) or shallow (called fish eye) will allow light to escape through the bottom or pavillion portion.
Diamonds are usually cut with 58 flat surfaces of facets. The size and location (in relation to other facets) are determined by a precise mathematical formula, designed to maximise a diamonds’ brilliance.
Some common cuts of diamond include:
• Round
• Princess
• Oval
• Marquise
• Emerald
• Heart
Source: AZoM.com