For grading purposes, the word "cut" means the proportions and finish - or make - of a polished diamond. Proportions are the agnels and relative measurements of a polished gem's facets and the relationships between them. Finish is the quality of the polish and the precision or symmetry of the cut. These factors, along with the thickness of the girdle, affect a diamond's overall cut grade.
The cut-grading system developed and used by GIA applies to standard round brilliant diamonds in all clarities across the D-to-Z color
range. It assigns one of five cut grades: Excellent, Very Good, Good, Fair, and Poor.
A well-cut diamond can make light perform in breathtaking ways, resulting in a magnificent display of three important diamond attributes: brilliance, fire, and scintillation.
- Brilliance: The combination of all the white light reflections from the surfae and the inside of a diamond.
- Fire: The flashes of color you see in a polished diamond.
- The flashes of light you see when the diamond, the light, or the observer moves.
- Proportions: The angles and relative measurements of polished diamond, and the relationships between them.
- Symmetry: The precision of its proportions and the balanced placement of its facets from one side to the other.
- Polish: The overall condition of the facet surfaces of a finished diamond.
- Facet: A flat, polished surface on a finished diamond.
- Crown: Top part of the diamond above the girdle.
- Girdle: The narrow section of a finished diamond that forms the boundary between the crown and the pavilion and funtions as the diamond's setting edge.
- Pavilion: Lower part of a faceted diamond below the girdle.
- Culet: Small facet at the bottom of a finished diamond.
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