If you want something of real value go for one carat or more.
Go for color G or H with G being the better. The lower in the alphabet, the better the color.
Inclusions are graded by slight inclusion, very slight inclustion or very slight inclustion. Perfect is simply way out of any normal person's price range.
From wikipedia -
https://en.wikipedia.org/wiki/Diamond_(gemstone)
Tolkowsky's calculations included some approximations. He calculated the ideal dimensions as:
- Table percentage (corner-to-corner diameter of the table divided by overall diameter) = 53%
- Depth percentage (overall depth divided by overall diameter) = 59.3% (not including adjustments for the culet height and girdle thickness)
- Pavilion angle (angle between the girdle and the pavilion main facets) = 40.75°
- Crown angle (angle between the girdle and the crown's kite facets) = 34.5°
- Pavilion depth (depth of pavilion divided by overall diameter) = 43.1%
- Crown depth (depth of crown divided by overall diameter) = 16.2%
The culet is the tiny point or facet at the bottom of the diamond. This should be a negligible diameter, otherwise light leaks out of the bottom. Tolkowsky's calculations included neither a culet nor a girdle. However, a girdle is required in reality in order to prevent the diamond from easily chipping in the setting. The thick part of the girdle is normally about 1.7% (of the overall diameter) thicker than the thin part of the girdle.
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The further the diamond's characteristics are from the Tolkowsky's ideal, the less light will be reflected. However, there is a small range in which the diamond can be considered "ideal". Tolkowsky's calculations can be repeated for a narrow range of pavilion angles. Such calculations show a slightly larger table percentage, and a trade-off between pavilion angle and crown angle.
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Today, because of the relative importance of carat weight among buyers, many diamonds are often intentionally cut poorly to increase carat weight. There is a financial premium for a diamond that weighs the desirable 1.0 carat (200 mg), so often the girdle is made thicker or the depth is increased. Neither of these changes makes the diamond
appear any larger, and both greatly reduce the sparkle of the diamond. (A poorly cut 1.0-carat (200 mg) diamond may have the same diameter and appear as large as a 0.85-carat (170 mg) diamond.) The
depth percentage is the overall quickest indication of the quality of the cut of a round brilliant. "Ideal" round brilliant diamonds should not have a depth percentage greater than 62.5%. Another quick indication is the
overall diameter. Typically a round brilliant 1.0-carat (200 mg) diamond should have a diameter of about 6.5 mm (0.26 in). Mathematically, the diameter in millimeters of a round brilliant should approximately equal to 6.5 times the
cube root of carat weight, or 11.1 times the cube root of gram weight, or 1.4 times the cube root of point weight.
