Cut · Chapter 07
How proportions shape light
Table, crown, pavilion, depth, girdle, and facet relationships—read as one optical composition.
Proportion numbers are most useful when they are read as relationships. No single measurement creates beauty in isolation, and no universal recipe describes every attractive diamond.
The table opens the view
The table is the large top facet. Its size influences the balance of brightness, fire, and facet pattern, but the same table percentage can behave differently with different crown and pavilion combinations.
The crown shapes fire and pattern
The crown is the portion above the girdle. Its angle and height work with the table and pavilion, influencing colored fire, face-up pattern, and the diamond’s overall profile.
The pavilion does much of the work of returning light
The pavilion sits below the girdle. Its angle and depth strongly influence where light travels after entering the diamond; combinations that are too shallow or too deep can produce areas of leakage or persistent darkness.
Total depth affects presence
Depth percentage relates the diamond’s depth to its width. Extra weight hidden below the girdle can reduce face-up spread, while a stone cut too shallow may sacrifice attractive light behavior or durability.
Girdle, culet, polish, and symmetry still matter
The girdle provides the setting edge and influences durability and weight distribution. The culet, facet alignment, and polish contribute to appearance and craftsmanship; they are not afterthoughts to the main angle pair.
Rounds and fancy shapes need different restraint
Round-brilliant research supports detailed proportion screening, yet even high-grade rounds can look different. Ovals, pears, cushions, radiants, emerald cuts, and other fancy shapes require more attention to outline, contrast, bow-tie, windowing, and video.
Worth remembering: Use numbers to narrow the field, then return to the actual face-up image.
Essential language
- Table percentage
- Table width expressed as a percentage of the diamond’s average width.
- Crown angle
- The angle of the bezel facets above the girdle in a round brilliant.
- Pavilion angle
- The angle of the main pavilion facets below the girdle in a round brilliant.
- Depth percentage
- Total depth expressed relative to a diamond’s width.
- Light leakage
- Light that exits away from the viewer instead of contributing to face-up return.
Questions to take with you
- How do the table, crown, pavilion, and depth work as a combination?
- Does the diamond carry excess weight that reduces face-up size?
- Are durability factors such as girdle thickness appropriate for the shape?
- What do neutral imagery and movement reveal that the proportion diagram cannot?