The term carat dates back to when gemstones were weighed using the carob as a counter balance. Unlike colour, clarity and cut, which are the result of visual assessment, carat weight is conclusively determined by weighing the stone on a diamond balance or scale.
Carat weight can be expressed as points, where:
1 carat (ct) = 100 points = 0.200 gram
Larger carat weight does not always equate to greater diamond value. The value of a diamond is determined by its rarity and the combination of all the four C’s: carat weight, colour, clarity and cut.
Two stones of equal carat weight can have vastly different prices if their colour, clarity or quality of cut differs.
The international colour grading system uses the letters, D to Z, to denote a colour, where D is colourless and the depth of colour increases down the scale to Z.
Colour grade is assigned by comparison to a master set of colour grading stones that each act as the borderline between two colour grades. D to Z grades are a range of tones of colour where one merges into the next.
There may be very little distinguishable difference between two diamonds that are close to each other on the scale, such as a low F colour and a high G colour.
Clarity grading uses a series of abbreviations to denote the size, number, location, type and intensity of inclusions as well as external blemishes. The type and arrangement if inclusions allows the stone to be identified.
As a diamond forms within the earth and travels to the surface, the extreme conditions make it rare that it will be perfect in every aspect.
Diamonds with fewer inclusions are rarer and, therefore, more valuable. Minor inclusions affect the price of the diamond even though they may not affect its overall beauty.
Very large inclusions that are more visible can obstruct the light paths in the diamond, resulting in reduced transparency.
The quality of the cut refers to the measurements of the diamond’s proportions, the symmetry of the facets and the quality of the polish.
Cut or make is the most critical factor in the overall beauty of a diamond.
For diamonds of different proportions, the light behaves differently as it enters and exits the stone. The combination of proportions can have a dramatic effect on a diamond’s face-up appearance, regardless of whether a stone is claw or bezel set.
A stone of high colour and clarity may still appear dark or lifeless if the quality of cut is poor, affecting its beauty and value.