Carat refers to the weight of a diamond. Often mistaken with size, carat is actually a measure of weight. The term carat is a derivative of the word carob. Carob seeds, which are surprisingly uniform in weight, were used as a reference for diamond weight in ancient civilisations. One carob seed equalled one carat. One carat is equivalent to 200 milligrams. One carat can also be divided into 100 ‘points’. A .75 carat diamond is the same as a 75-point or 3/4 carat diamond.
Clarity refers to the presence of inclusions in a diamond. Inclusions are ranked on a scale of perfection, known as clarity. The clarity scale, ranging from F (Flawless) to Included (I), is based on the visibility of inclusions at a magnification of 10x. Even with a loupe, the birthmarks in the VVS (Very, Very Slightly Included) to VS (Very Slightly Included) range can be very difficult to find. It is only when a diamond is graded 'I' that it is possible to see the birthmarks with the naked eye. The position of inclusions can affect the value of a diamond and you should consider the number, size, brightness, nature and position of inclusions.
Colour refers to the degree to which a diamond is colourless. Diamonds can be found in many colours, however white-coloured or colourless diamonds remain the most popular. Diamonds are graded on a colour scale which ranges from D (colourless) to Z. Warmer coloured diamonds (K–Z) are particularly desirable when set in yellow gold. Icy winter white coloured diamonds (D–J) look stunning set in white gold or platinum. Nature has also created diamonds in shades of blue, green, yellow, orange, and pink. Red is the rarest of all. These diamonds are called ‘coloured fancies’ and are extremely rare and highly treasured.
Cut refers to the angles and proportions of a diamond. It is the only one of the 4Cs that is influenced by the human hand. Diamond cutting requires great skill and training. The cutter must polish tiny surfaces known as facets onto the rough diamond. This process is what creates the facets known as the crown, culet, table, girdle and pavilion of the diamond.