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The Most Important C

Cut is considered by many to be the most important "C". Only when precisely calculated planes and angles are used, does the stone achieve its greatest possible beauty. A badly cut diamond, no matter how good its color and clarity will not match the fire and brilliance of a better-cut diamond with comparatively lower color and clarity.
 
 

View Diamond Parts in more detail.
  Experts express differing opinions on the best table size (the diameter of the largest facet on the top of the stone) and the best depth for a diamond, because these factors alone are not sufficient to accurately judge its cut.

Other factors - crown angle, girdle thickness, pavilion depth-percentage (the ratio of depth to girdle diameter), culet size, polish and symmetry - also play a role in judging a diamond's overall cut quality.
 

Light Emission

A well-cut diamond will reflect most of the light back to the observer's eye. A poorly cut diamond will reflect only a small proportion of the light that enters it.
 
Well cut diamond - most light is reflected back to the observer. Cut too deep; pavilion is too thick - most light is lost through the side of the stone. Cut too shallow; pavilion too flat - most light is lost through the bottom of the stone.
Light source and travel path of the majority of light
Less intense refracted light
 

Diamond Cut guides

We at Gem Nation use the following data tables as a guideline to understanding cut grades for brilliant diamonds. Round diamonds are the only shape that can be realistically evaluated with these measures. Other shapes, however, are also dependent on other factors and mere mathematical formulae will not necessarily determine a diamond's magnficence.

The data presented here is a composite of information from a multitude of sources, including definitions of the Tolkowsky Brilliant, Scandinavian Standard Brilliant, Eulitz Brilliant, and the AGS Laboratories' Ideal cut, together with our own gemologists' knowledge and experience.

Round

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 59.5 - 61.9 59.1 - 62.3 58.5 - 63 57.5 - 63.5 57 - 64 56 - 67 <56 >67
Table % 55 - 57 53 - 58 52 - 60 51.5 - 63 51 - 65 50 - 70 <50 >70
Symmetry VG - EX G - EX G - EX G-EX All All All
Culet None None - Med None - Sl. Large None - Large None - Large None - Very Large None - Extr. Large
Girdle Thin, Med, Sl Thk Thin, Med, Sl Thk, Thk Thin, Med, Sl Thk, Thk Very Thn - Thick Very Thn - Very Thick Ext Thn - Ext Thick Ext Thn - Ext Thick
Polish VG - EX G - EX G - EX All All All All
Clarity SI1 - FL SI1 - FL All All All All All

Princess

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 65 - 70 63 - 70 62 - 73 62 - 75 56 - 82 55 - 86 <55 >86
Table % 65 - 72 65 - 72 62 - 74 57 - 78 55 - 85 57 - 89 <57 >89
Ratio L:W 1:1 - 1.05:1 1:1 - 1.10:1 1:1 - 1.75:1 1:1 - 1.75:1 1:1 - 2:1 1:1 - 2:1 1:1 - 2:1

Radiant

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 63 - 70 63 - 70 63 - 72 62 - 74 56 - 78 55 - 83 <55 >83
Table % 68 - 72 68 - 72 67 - 74 65 - 78 63 - 80 53 - 83 <53 >83
Ratio L:W 1:1 - 1.05:1 1:1 - 1.15:1 1:1 - 1.75:1 1:1 - 1.75:1 1:1 - 2:1 1:1 - 2:1 1:1 - 2:1

Emerald

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 61 - 67.5 61 - 67.5 61 - 69 60 - 70 58 - 75.5 54.5 - 81 <54.5 >81
Table % 62 - 69 62 - 69 62 - 71 61 - 72 56 - 75 55 - 82 <55 >82
Ratio L:W 1.3:1 - 1.4:1 1.2:1 - 1.75:1 1.05:1 - 2:1 1.05:1 - 2:1 1.05:1 - 2:1 1.05:1 - 2:1 1.05:1 - 2:1

Oval

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 59 - 62 59 - 62 59 - 63 57.5 - 65.5 55 - 69 46 - 76 <46 >76
Table % 57 - 60 57 - 60 54 - 61.5 52 - 64 51 - 66 50 - 71 <50 >71
Ratio L:W 1.4:1 - 1.6:1 1.35:1 - 1.65:1 1.3:1 - 1.7:1 1.1:1 -1.90:1 1.1:1 -1.90:1 1.1:1 -1.90:1 1.1:1 -1.90:1

Pear

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 59 - 63 59 - 63 59 - 64 58 - 65 54 - 69 51 - 73 <51 >73
Table % 57 - 60 57 - 60 54 - 62 53 - 64 51 - 66 48 - 70 <48 >70
Ratio L:W 1.6:1 - 1.7:1 1.5:1 - 1.75:1 1.25:1 - 1.85:1 1.2:1 - 1.9:1 1.1:1 - 2.0:1 1.1:1 - 2.0:1 1.1:1 - 2.0:1

Marquise

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 59 - 63 59 - 63 58 - 64 57.5 - 65 54.5 - 69 50.5 - 75 <50.5 >75
Table % 57 - 60 57 - 60 55 - 62 53 - 64 51 - 66 50 - 70 <50 >70
Ratio L:W 1.9:1 - 2.1:1 1.75:1 - 2.25:1 1.70:1 - 2.3:1 1.60:1 - 2.4:1 1.50:1 - 2.5:1 1.50:1 - 2.5:1 1.50:1 - 2.5:1

Heart

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 57 - 59 57 - 59 56 - 60 54 - 60 51 - 62 46 - 67 <46 >67
Table % 57 - 60 57 - 60 54 - 62 53 - 64 51 - 66 48 - 70 <48 >70
Ratio L:W 0.98:1 - 1.02:1 0.90:1 - 1.10:1 0.85:1 - 1.15:1 0.82:1 - 1.18:1 0.80:1 - 1.20:1 0.80:1 - 1.20:1 0.80:1 - 1.20:1

Cushion

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 59 - 62 59 - 62 58 - 64 57 - 69 55 - 73 50 - 80 <50 >80
Table % 57 - 60 57 - 60 54 - 62 52 - 70 51 - 75 50 - 80 <50 >80
Ratio L:W 1:1 - 1.05:1 1:1 - 1.10:1 1:1 - 1.12:1 1:1 - 1.15:1 1:1 - 1.20:1 1:1 - 1.20:1 1:1 - 1.20:1

Trillliant

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 40 - 42 40 - 42 38 - 44 37 - 45 35 - 48 30 - 54 <30 >54
Table % 58 - 60 57 - 60 54 - 62 52 - 65 51 - 67 48 - 72 <48 >72
Ratio L:W 0.98:1 - 1.02:1 0.95:1 - 1.05:1 0.92:1 - 1.08:1 0.90:1 - 1.10:1 0.88:1 - 1.12:1 0.88:1 - 1.12:1 0.88:1 - 1.12:1

Asscher

  Premium Ideal Ideal Excellent Very Good Good Fair Poor
Total Depth % 59 - 67 59 - 67 59 - 69 57 - 72 55 - 75 50 - 78 <50 >78
Table % 57 - 60 57 - 60 53 - 62 52 - 72 51 - 75 50 - 78 <50 >78
Ratio L:W 1:1 - 1.02:1 1:1 - 1.05:1 1:1 - 1.05:1 1:1 - 1.08:1 1:1 - 1.08:1 1:1 - 1.08:1 1:1 - 1.08:1

 
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