Cut is possibly the most important of the four Cs. For round brilliant diamonds, cut refers to the quality of workmanship (proportion and arrangement of facets), not the shape. The amount of brilliance, sparkle, and fire displayed by a diamond is determined by the quality of its cut. The scale runs from 'Excellent' to 'Poor.' The majority of diamonds on the market are cut from 'Excellent' to 'Very Good.' Diamonds with a cut grade of 'Poor' will appear lifeless and dull.
The absence of colour in a diamond is measured by colour. This is due to the fact that most "colourless" or "white" diamonds contain trace amounts of yellow, brown, or grey colour. A diamond with less colour is more desirable and valuable. The D-to-Z colour scale has 23 colour grades, with D indicating that a diamond has no detectable colour and Z indicating that a diamond has "light" colour. Any diamond with a colour grade greater than Z is considered a fancy colour diamond and is graded on a different colour scale.
The price of a stone is affected by colour grade, but differences of one to three colour grades are not easily discernible to untrained eyes. Diamond graders examine diamonds face down in special environments to detect subtle colour variations.
Diamonds of the D, E, and F grades are extremely rare and valuable. G and H diamonds are generally thought to be good buys. Color becomes more visible in grades I and lower. Clarity is determined by the number, size, and location of internal 'inclusions' and external 'blemishes.' Small crystals or fissures within the diamond are examples of inclusions. Chips are examples of blemishes. The grades range from 'Flawless,' which means a diamond has no visible flaws at 10x magnification, to 'Included,' which means a diamond has a significant number of flaws. Eye-visible inclusions are uncommon in diamonds with VS2 (Very Slightly Included) or SI1 (Slightly Included) grades.
These diamonds can be very affordable. Diamonds I1 (Included) or lower have visible inclusions that can make the diamond appear less appealing; some of these inclusions may also have an impact on the diamond's durability. Because the pattern of the facet arrangement obscures inclusions better, brilliant-cut diamonds have lower clarity characteristics than step cut diamonds. When purchasing a step cut diamond (such as an emerald cut), you may need to go higher in colour and clarity than when purchasing a brilliant-cut diamond.
Carat is the weight of a diamond. In general, the larger the diamond appears and the more valuable the stone, the higher the carat weight. The proportions of a diamond also influence its size. A one-carat diamond that is wider but has shallow proportions, for example, will appear larger than a one-carat diamond that has excellent proportions.
As the carat weight of a diamond increases, its price rises exponentially. They increase more at specific "magic sizes," such as 0.5, 1.0, 1.5, and 2.0 carats, for example. Buying just below a "magic size," such as a 0.95 carat diamond instead of a 1.0 carat diamond, can save money without sacrificing visual impact.