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Round Brilliant, Ideal, and Old Mine Cut
A Round Brilliant Cut's measurements are expressed as the depth and width.
To measure the depth of the stone, measure the length from the table to the culet
(see Table and Depth Percentage Formulas). The width or diameter is
measured from one side to the opposite side of the girdle.
To determine the approximate weight of a Round Brilliant Cut diamond, make
the following calculation:
Approximate carat weight of a Round Brilliant Cut diamond=Diameter
x Diameter x Depth x 0.0061
(The above weight formula provides an estimate. The actual weight may vary
up to 10%, depending on the make, girdle thickness, and accuracy of the measurement
tools.)
The Ideal Cut diamond is the industry standard for a perfectly
proportioned Round Brilliant Cut diamond. It's has 58 facets, and a Table % between 55%
& 57%. Its Depth % is between 59.3% & 60.9%. (See page 3 for formulas). The crown
encompasses 16.2% of the diamond's depth. The pavilion is 43.1% of the diamond's depth.
The crown is at a 34.5o degree angle. The pavilion angle is 40.75o.
An Old Mine Cut diamond was cut over 75 years ago. It is
characterized by a high crown, off round shape, extremely large culet, small table, and
very short lower girdle facets. To recut an Old Mine Cut to a modern cut, the diamond will
lose 15-25% of its original weight. In order to estimate the value of old mine cuts, grade
the color and clarity of the diamond, deduct 15-25% from the original weight, and look up
the price per carat on the corresponding chart for the lower weight.
Round Brilliant Cut MM and Corresponding Carat Weights
Chart Not to Scale. Weights may vary up to 20% with
make. Please specify weight requirements when ordering.
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