The Cut is a measure of proportions of the diamond.
The Cut determines
• The diamond’s brilliance and beauty
• The diamond’s ability to reflect light
• The diamond’s proportions, symmetry and finish
A well-cut diamond appears brilliant and fiery, while a badly cut diamond looks dull and lifeless, despite having a good colour and clarity grade.
The Cut is a set of measurements based on how light travels within the diamond and exits from the top. The Cut is the only “man-made” C of the 4C’s.
Gemmologists consider Cut the single most important factor that defines the brilliance of a diamond.
Do not confuse Cut with Shape. Cut refers to how well the diamond has been designed and proportioned by the cutter. Shape refers to the general silhouette or outline of the diamond.
An ideally proportioned diamond is cut according to scientific formulae calculated to maximise brilliance. In such diamonds, light that enters the stone from the top will bounce about within the diamond to create multiple reflections, which exit the stone from the top, causing the diamond’s glitter.
Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom. The result is less brilliance, and ultimately less value for the diamond.
The most important proportion is the ratio between the depth and the diameter of the diamond. The ideal ratio is 58.5%, but slight deviations are acceptable. The ratio between the height of the crown and that of the pavilion is also important. Please remember that this ideal ratio applies only to the Round Brilliant shaped diamonds. Gemologists differ on the ideal depth percentages to be followed in the other fancy shapes, and therefore, no ratios have been set as ideal for any of the other shapes.
Other factors that count are length of the pavilion facets, size and shape of the various crown facets, size of the table and the culet.
Polish and Symmetry
• Dramatically amplifies brilliance of a well-proportioned diamond
• Is crucial in diamonds of very high clarity grades
• Gives the diamond its final appearance
• Is crucial to its brilliance
• Ensures smooth passage of light through the diamond
Diamonds with poor polish are less brilliant due to microscopic polish lines that reduce the amount of light that enters and exits the stone.
Rating of the Cut
The Gemmological Institute of America (GIA), the authority in diamond certification, grades diamond cuts as Excellent, Very Good, Good, Fair, or Poor.
The GIA determines cut grades on the basis of:
• Brightness, Fire, and Scintillation
• Weight Ratio and Durability
• Polish and Symmetry
What is the best cut grade
• If you are looking for the most exceptional diamonds that can attain the highest gemological standards, do not look beyond CaratLane Signature Collection. These diamonds are cut to the exact proportions to get the maximum brilliance. They have the best polish and symmetry grades available for round diamonds, and our signature fancy shapes have either ‘excellent’ or ‘very good’ polish and symmetry grades.
• If you are looking for a round brilliant diamond that gives the best value for your money, choose a diamond with a cut grade of ‘good’ or ‘very good’, and polish and symmetry grades of ‘very good’ or ‘good’.
• If the diamond you have selected has an ideal- or very-good cut with very good or good polish and symmetry, you can buy lower grades of color and clarity — look for a diamond with G or H color and SI1 or SI2 clarity.