The first thing to know is that the cut of a diamond indicates more than its shape. The cut also determines how sparkly your diamond will be! It’s not enough that a diamond is big and clear and white. No diamond can be truly attractive unless it sparkles, and it won’t sparkle unless it’s properly cut. You can buy a one-carat diamond, graded SI2 or higher for clarity, and rated J or better on the color scale, and it still won’t sparkle unless the cut is good.

To understand what I mean, first let’s look at some shapes. Diamonds can be cut into a wide variety of shapes. The following are some of the most popular:

CLASS I

• Table: 53-60% of diameter of stone for round, marquise, pear and oval; 58-64% of diameter of stone for emerald and rectangular
• Total depth: 59.3-61% of diameter of stone for round, marquise, pear and oval; 58-64% of diameter of stone for emerald and rectangular
• Crown angle: 34-35 degrees for round, marquise, pear and oval 33-35 degrees for emerald and rectangular
• Crown height: 13.5-16.2% of diameter of stone for round, marquise, pear and oval and 11.7-16.2% of diameter of stone for emerald and rectangular
• Girdle thickness: .7-1.7% of diameter of stone (medium)
• Pavilion angle: 40.20 to 41.20 degrees for rounds; 39.25 to 40.75 degrees for marquise, pear and oval; 43.8 to 46.8 degrees for emerald and rectangular
• Pavilion depth: 42.52-43.57% of diameter of stone for round, marquise, pear and oval; 47.6-53.1% of diameter of stone for emerald and rectangular

CLASS II

• Table: 53-64% for round, pear, marquise and oval; 53-65% for emerald and rectangular
• Total depth: 56-61% for round, marquise, pear and oval; 56-65% for emerald and rectangular
• Crown angles: 32-35 degrees for all shapes
• Crown height: 11.2-16.2% for all shapes
• Girdle thickness: Thin to thick for all shapes (medium preferred)
• Pavilion angle: 40 to 41.5 degrees for rounds; 39.25 to 40.75 degrees for pear, marquise and oval; 43.3 to 46.8 for emerald and rectangular
• Pavilion depth: 42.31-43.89% for rounds; 41.51-43.1% for pear, marquise and oval; 47.1-53.1% for emerald and rectangular
• Polish & symmetry: Good

CLASS III

• Table %: 65-70% for round, marquise, pear and oval; 66-70% for emerald and rectangular
• Crown angles: 30-32 degrees for all shapes
• Girdle thickness: Very thin or very thick for all shapes
• Pavilion angle: Any measurement other than 40 to 41.5 degrees for rounds or 39.25 to 40.75 degrees for marquise, pear and oval; any measurement other than 43.3 to 46.8 degrees
• Polish & symmetry: Fair to good

CLASS IV (50-60% below cost)

• Table %: 70% and above for all shapes
• Crown angles: 30 degrees and below for all shapes
• Girdle thickness: Extremely thin to very thin or very thick to extremely thick for all shapes
• Pavilion angle: Any measurement other than 40 to 41.5 degrees for rounds or 39.25 to 40.75 degrees for marquise, pear and oval; any measurement other than 43.3 to 46.8 degrees
• Polish & symmetry: Fair to poor

by Fred Cuellar, author of the best-selling book “How to Buy a Diamond.” More questions? Ask the Diamond Guy®